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                                      EPA-450/3-77-004a
          POPULATION EXPOSURE
TO OXIDANTS AND NITROGEN DIOXIDE
                IN LOS ANGELES
    VOLUME I: EXECUTIVE SUMMARY
                           by

                   Yuji Horie and Anton S. Chaplin

                    Technology Service Corporation
                      2811 Wilshire Boulevard
                    Santa Monica, California 90403

                           and

                  Neil H. Frank and William F. Hunt, Jr.

                   Environmental Protection Agency
                  Monitoring and Data Analysis Division
                Office of Air Quality Planning and Standards
                      Contract No. 68-02-2318
                      Project No. DU-76-C190
                    Program Element No. 2AF643
                   EPA Project Officer: Neil H. Frank
                         Prepared for

                ENVIRONMENTAL PROTECTION AGENCY
                   Office of Air and Waste Management
                Office of Air Quality Planning and Standards
                Research Triangle Park, North Carolina 27711

                         January 1977

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This report is issued by the Environmental Protection Agency to report
technical data of interest to a limited number of readers.  Copies are
available free of charge to Federal employees, current contractors and
grantees, and nonprofit organizations - in limited quantities - from the
Library Services Office (MD-35) , Research Triangle Park, North Carolina
27711; or, for a fee, from the National Technical Information Service,
5285 Port Royal Road,  Springfield, Virginia 22161.
 This report was furnished to the Environmental Protection Agency by
 Technology Service Corporation, 2811 Wilshire Boulevard, Santa Monica.
 California 90403,  in fulfillment of Contract No. 68-02-2318, Project No.
 DU-76-C190, Program Element No. 2AF643.  The contents of this report
 are reproduced herein as received from Technology Service Corporation.
 The opinions, findings, and conclusions expressed are those of the
 author and not necessarily those of the Environmental Protection Agency.
 Mention of company or product names is not to be considered as an endorse-
 ment by the Environmental Protection Agency.
                      Publication No. EPA-450/3-77-004a
                                11

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                           TABLE OF CONTENTS
SECTION
      6.2  TEN-YEAR TREND FOR N02
HIGHLIGHTS .............................     v

LIST OF FIGURES ...........................    i*
                                                                         XI
LIST OF TABLES ...........................

 1. ~  INTRODUCTION  .........................     !

 2.   DESCRIPTION OF THE STUDY AREA .................     3

 3.   DEMOGRAPHIC DATA  .......................     5

 4.   SUMMARY OF AIR QUALITY DATA ..................     7

 5.   POPULATION EXPOSURE ANALYSIS FOR 1973 DATA  ..........      9

      5.1  WEEKDAY/WEEKEND DIFFERENCE IN AIR QUALITY AND IN
           POPULATION EXPOSURE   ...................      9

      5.2  EFFECTS OF DAILY POPULATION MOBILITY ON POPULATION
           EXPOSURE   ........................     11

 6.   TRENDS IN AIR QUALITY AND  IN POPULATION EXPOSURE  .......     13

      6.1  TEN-YEAR TREND FOR 0
 7.   REFERENCES   ..........................     19

 APPENDIX A  SUMMARY OF AIR QUALITY DATA OBSERVED AT MONITORING
             STATIONS  ........................    A-l
                                    m

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                             HIGHLIGHTS

     Detailed analyses  for a  single year  (1973)  and  trend  analyses  for
1965-1974 reveal  the following results  concerning  population  exposure to
oxidants (0 ) and nitrogen dioxide (N02)  in  the  Los  Angeles Basin:
           A
ANALYSIS OF WEEKDAY/WEEKEND EFFECTS  AND IMPACT OF  POPULATION  MOBILITY ON
POPULATION EXPOSURE USING 1973 DATA
     1.  On an annual basis the population as a  whole is exposed to Ox
         air pollution exceeding the NAAQS on a  smaller percentage of
         days and a smaller percentage of hours  during the weekends
         than the weekdays.
     2.  The population exposure to N02 above the California Standard is
         less during the weekends than the weekdays in both the percentage
         of  days  and the  percentage of hours.
     3.  Because  of daily  population mobility between residence and work-
         place, workers as a  whole are exposed  less to QX above the NAAOS
          than nonworkers.  In contrast workers  experience a  greater number
          of hours of exposure to  N02 above  the  California Standard than
          nonworkers.
      4.   Although incorporation of  daily population mobility into a popu-
          lation exposure  analysis is  important  for  identifying the
          population-at-risk  distribution,which  describes  the percentage
          of the population exposed  to  a concentration above  the standard
          for a given fraction of  the time, the  population mobility con-
          sideration has turned out not to be critical in determining the
          aggregated indices of population exposure.

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ANALYSIS OF TRENDS IN POPULATION EXPOSURE FOR THE PERIOD 1965-1974


     1.  There has been a regionwide downward trend in both 0  air
                                                             J\


         pollution and population exposure to  DX above the NAAQS during



         the 10-year study period (Figure 15).


     2.  There has been a sharper reduction in population exposure to


         the higher 0  concentrations and in the frequency of violations
                     /\


         of two and three times the NAAQS (Figure 17).


           The percentage of the total population exposed to QX levels



            above the NAAQS  (160 yg/m3--one-hour average) more than 180



            days  per year dropped from 53% in 1965/66 to a mere 5% in



            1973/74  (Figure  17).


         t  The percent  of the  total population  exposed to QX above the



            NAAQS more  than  75  days  per  year was reduced  from 100% in



            1965/66  to  36% in  1973/74  (Figure 17).


      3.  Practically the entire population  in the Southern half of


          Los  Angeles County  has been exposed to N02 annual  mean concen-


          trations above the  NAAQb (100 yg/m3) during the  10-year period



          (Figures 19 and 20).


      4.  There is no clear trend in either N02  air quality or population


          exposure to N02.  However, the higher percent!le concentrations


          and the population exposure to such concentrations have fallen



          in recent years (Figures 21 and 23).
                                     VI

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5.  The percentage of the population exposed to one-hour NC^ concen-
    trations above the California Standard at least 22 days per year
    has been reduced from 65% in 1965/66 to 35% in 1973/74 (Figure 23)
                               VII

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                             LIST OF FIGURES


TITLE                                                              AE_

1   BOUNDARIES SHOWING TREND ANALYSIS AREA, 1973 ANALYSIS
    AREA, AND LOS ANGELES AQCR .................    19

2.  LOCATION OF MONITORING STATIONS  ..............    20

3.  TOPOGRAPHICAL FEATURES OF THE LOS ANGELES BASIN  ......    21

4.  POPULATION DENSITY  IN PERSONS PER SQUARE MILE IN 1970   ...    22

5.  NUMBER OF PERSONS EMPLOYED PER SQUARE MILE IN 1970  .....    23

6.  PERCENT  CHANGE  IN POPULATION 1965 TO 1975  .........    24

7.  PERCENT  CHANGE  IN EMPLOYMENT FROM 1965 TO 1975  .......    25

8.  ISOPLETHS OF  PERCENT OF  DAYS ON  WHICH THE NAAQS  FOR OXIDANT
    WAS  EXCEEDED  IN 1973  ....................     26

 9   ISOPLETHS OF  AVERAGE DURATION  (HOURS) ON DAYS WHEN  THE
    NAAQS FOR OXIDANT WAS EXCEEDED  IN 1973    ..........     27

10  THE  DIFFERENCE  IN PERCENT OF THE NUMBER OF DAYS  ON  WHICH
    THE  NAAQS  FOR OXIDANT WAS EXCEEDED  IN  1973,  WEEKDAY MINUS
     WEEKEND   ..........................     Zb

11   ISOPLETHS  OF  PERCENT OF  DAYS ON WHICH THE CALIFORNIA ONE
     HOUR STANDARD FOR N02 WAS EXCEEDED  IN  1973  .........     &

12   ISOPLETHS  OF  AVERAGE  DURATION  (HOURS)  ON  DAYS  WHEN  THE
     CALIFORNIA ONE  HOUR STANDARD FOR N02 WAS  EXCEEDED IN 1973. .      30

13   THE DIFFERENCE  IN  PERCENT OF THE NUMBER OF  DAYS ON  WHICH
     THE CALIFORNIA ONE  HOUR STANDARD FOR N02 WAS EXCEEDED
     IN 1973, WEEKDAY MINUS  WEEKEND  ...............      -31
14.  THE NET INFLUX OF POPULATION (WORKERS) DURING WORKING
     TIME IN 1970
15   PERCENT OF DAYS ON WHICH THE NAAQS FOR OXIDANT WAS
     EXCEEDED DURING FIVE 2-YEAR PERIODS
 16   AVERAGE DURATION  (HOURS) ON DAYS WHEN THE NAAQS FOR OXIDANT
     WAS EXCEEDED DURING FIVE 2-YEAR PERIODS  ..........     34
                                      IX

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                        LIST OF FIGURES (Cont'd)


TITLE                                                                PAGE

17.  CHANGES IN POPULATION EXPOSURE TO 03 DURING FIVE 2-YEAR
     PERIODS	   35

18.  THE AVERAGE VALUE AND THE RANGE OF VALUES FOR EIGHT
     MONITORING STATIONS SHOWING N0? TRENDS IN ANNUAL MEAN
     CONCENTRATIONS	   36

19.  N02 ANNUAL MEAN CONCENTRATION	   37

20.  CHANGES IN THE TOTAL POPULATION EXPOSURE TO N0? DURING FIVE
     2-YEAR PERIODS	   38

21.  PERCENT OF DAYS ON WHICH THE CALIFORNIA 1-HR STANDARD FOR
     N02 WAS EXCEEDED DURING FIVE 2-YEAR PERIODS  	   39

22.  AVERAGE DURATION (HOURS) ON DAYS WHEN THE CALIFORNIA ONE
     HOUR STANDARD WAS EXCEEDED DURING FIVE 2-YEAR PERIODS  ....   40

23.  CHANGES IN POPULATION EXPOSURE TO N0? DURING FIVE  2-YEAR
     PERIODS	   41

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                        LIST OF TABLES


TITLE                                                            PAGE

1.  Characteristics of Study Areas 	      5

2.  Regionwide Impact of Weekday/Weekend Effect on
    Population Exposure to 0  and N09 in 1973	     10
                            /\       

3.  Effect of Population Mobility Consideration on the
    Population-at-Risk Indices of All Workers and Total
    Population (Percent of Hours Exceeded) 	     12

4.  Regionwide Trend in Average No. of Days NAAQS for QX
    was Exceeded and the Average Duration of Excess Air
    Pollution in Hours per Day	     14

5.  Regionwide Trend in Average No. of Days Per Year the
    California Standard for N02 was Exceeded and the
    Average Duration of Violations in Hours per Day  	     17
                               XI

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                         1.    INTRODUCTION
                                                                     *
     This report summarizes  the major findings  of two related  reports
which present the salient results of studies  on population  exposure to
photochemical oxidants (Ox)  and nitrogen dioxide (N02) in the  Los  Angeles
Basin.  The emphasis of this executive summary  report is centered  on a
description of the results rather than interpretation.  At the conclusion
of this project the final report will attempt to interpret the results  of
our research with regard to what is known about emission sources,  meteor-
ology, air quality, and population distributions in the Los Angeles Basin.
     To determine population exposure to air pollution, air quality measure-
ments taken at widely separated monitoring stations were interpolated to
provide the spatial distribution of pollutant concentrations.   Demographic
data were merged with the air monitoring data to estimate the short-term
and the long-term concentrations experienced by the Los Angeles population.
     The first part of this report examines special features of population
exposure in the Los Angeles Basin using detailed data for 1973.  These
features include weekday-weekend differences in air quality and the  effec:
of diurnal population mobility on population exposure.  The second part of
       Horie, Y., A. Chaplin, and E. Helfenbein, "Population Exposure to
 Oxidants and Nitrogen  Dioxide in Los Angeles, Volume II.  Week/Weekend
 and Population Mobility Effects," U.S. EPA/OAQPS Publication #EPA-450/3-
 77-004b, Technology Service Corporation,  January,  1977.
       Horie, Y. and A. Chaplin, "Population  Exposure to Oxidants and
 Nitrogen Dioxide in Los Angeles, Volume  III.  Long Term Trends, 1965-
 1974," U.S. EPA/OAQPS  Publication #EPA-450/3-77-004c, Technology Service
 Corporation,  January, 1977.

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this report describes the spatial  change in air quality and the regionwide
trends in population exposure for  the 10-year period from 1965 to 1974.
     Hourly 0  air quality data and annual  mean N02  air quality data  are
examined in relation to the primary National  Ambient Air Quality Standards
(NAAQS) which are designed to protect the public health.  Hourly N02  air
quality data are also examined in  relation to the California one-hour Air
Quality Standard.
     The remainder of this report  is divided into five sections which
describe the methodology and the results.  The five  sections are:
     2.0  A description of the study area,
     3.0  A summary of relevant demographic data,
     4.0  A summary of the air quality data,
     5.0  A detailed analysis of population exposure in 1973, and
     6.0  An analysis of trends in air quality and in population ex-
          posure over the ten-year period 1965-1974.

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                  2.   DESCRIPTION  OF  THE  STUDY AREA

     The regions under study are three  subsets of the  Los Angeles AQCR.   As
shown in Figure 1, the area for which the 1973 analyses  were  performed  dif-
fers only slightly from that of the LA-AQCR.  The area for  which the  QX
trend analyses were performed (as  shown by the dark  boundary  line)  is much
smaller than the AQCR, because only in  this limited  region  is the data  base
adequate for trend analyses.  For  a similar reason,  the  N02 trend analysis
area, denoted by the slanted lines, is  even smaller.
     Figure 2  shows the locations of the air monitoring stations.   Data from
22  stations monitoring 0   and  26  stations monitoring  N02 were used for the
                        /\
1973 analyses.   For the 10-year trend  study, ten  stations monitoring QX and
eight  stations monitoring  N02  were included in the  analyses.  Because  fewer
N02 stations  were included in  the trend  analysis, the study  area for N02
trend  analysis is only the Los Angeles county portion of the QX trend  anal-
ysis area.   Figure 3  illustrates  the topographical  features  of the study
reg i on.

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                      3.    DEMOGRAPHIC  DATA

     The population and employment statistics  prepared  by the  Southern
California Association of Government (SCAG) and the 1970 census  data were
used to develop a demographic network.   The demographic network  consists
of a number of receptor points at which local  population data  and local
air quality data are merged to compute population exposure variables.  The
air quality of each receptor point is  estimated from the actual monitoring
data by spatial interpolation [2].
     The  SCAG data are reported according to Regional Statistical Areas
 (RSA's).  One receptor point is assigned to each RSA irrespective of its
 population size and land area.  An additional  receptor  point  is assigned
 for each  increment of  population  by  200,000 or land area by 200 square
 miles.  A description  of the study areas is given  below in Table 1.
                    Table 1.  Characteristics of Study Areas

    Type of Analysis
        1973 analysis
    0  trend analysis
     /\
    N02 trend  analysis

   estimated population in  1973
   estimated population in  1970
 Figures 4 and 5 depict the spatial  variation  of population  density  and of
 employment  density over the study region.   Figures 6  and 7  present  the

Population Size
9,899,814
**
8,548,431
**
6,858,390
Land Area
(square miles)
8612
2316
1509
No. if
Receptors
99
58
45

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percent change that occurred in population and in employment in  each  RSA
during the 10-year period 1965 to 1974.   It can be seen  from Figures  4 and
5 that the population density and the employment density are spatially
correlated to each other but the latter is more concentrated around the
downtown Los Angeles area.   A comparison between Figures 4 and 5 and  Figures
6 and 7 shows that the growth in both population and number of employments
is higher in the fringe areas than the urban core areas  of Los Angeles and
Long Beach cities.

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                4.   SUMMARY OF AIR QUALITY  DATA





     The national  ambient air quality standard (NAAQS)  for oxidants  (Ox)



is a one-hour average of 160 yg/m3 (~8 pphm).   The NAAQS for N02  is  an

                                                o

annual arithmetic mean concentration of 100 yg/m  (~5 pphm).  The California



one-hour standard for N02 is 470 yg/m3 (~25 pphm). The information described



in this report is interpreted with reference to these three standards.



     For the 1973 detailed analysis of special features of population



exposure, all of the hourly average and daily maximum hourly average air



quality data available from each air monitoring station in the region were



used to compute percentile concentration statistics.  The percentile statistics



of the daily concentrations were made for three time categories:   all time,



weekdays, and weekends.   In addition, the percentile statistics of the hourly



concentrations were made  for two time categories:  working time,  and non-



working time.  Tables Al  and A2 give the percent of days  per year exceeding



the NAAQS for 0 and  the  California standard  for N0? along with the avtr ge
               A                                   ~


duration in  hours for those days on which the  standard was  exceeded.



      For the ten-year trend analysis, the "Ten-Year Summary of California



Air Quality  Data 1963-1972" and its supplements  for  1973  and  1974 [4], were



used  to develop percentile  concentration statistics  for five  two-year periods:



1965/66, 67/68, 69/70,  71/72,  and  73/74.  The data were grouped  into two-year



periods so  that  historical  continuity could be maintained at  a maximum



number of sites. Tables  A3 and A4  give  the  percent  of  days  the standard was



exceeded and the average duration  in  hours  that the  violation occurred for




0  and N0?, respectively, during  each of these two-year periods.  Table A5
  X       


 lists the  annual  arithmetic mean  concentration of N02 for each of the  two-


                                                                       

year periods.

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                  5.    POPULATION  EXPOSURE  ANALYSIS  FOR  1973  DATA

     Population exposure to air pollution  is  characterized  by using  two
variables:   the percentage of the  population  exposed to  a pollutant  con-
centration  above the standard, i.e.,  the population-at-risk,  and the average
percent of time that people in a region are exposed  to a pollutant concen-
tration above the standard.  These quantities were determined for  different
populations (workers and non-workers) and for different time  periods (working
time, non-working time, weekday and weekend).
5.1  WEEKDAY/WEEKEND DIFFERENCE IN AIR QUALITY AND IN POPULATION  EXPOSURE
     Air quality data for 1973 were analyzed to quantify the  weekday/weekend
differences [4] in air quality and population exposure.  This time period
was selected because it offered the maximum number of monitoring stations
producing a complete year of data.
5.1.1  Weekday/Weekend Difference in QX
     Isopleths describing the  percentage of days the DX NAAQS is exceedei
are shown in Figure 8.  The  lowest percent (10% or  less) of  days exceedir.q
the standard is found  in  the  coastal area  and the highest  percent (50% or
more)  in the inland area.  Figure 9  shows  isopleths of  average duration  in
hours  for those days on which  the standard was exceeded.   The average dura-
tion is also the shortest (4 hours per day or less)  in  the coastal  area  and
the  longest  (7 hours per  day or more)  in  the inland area.
     Figure  10 presents differences  in daily Ox frequency  of violation be-
tween  weekdays and  weekends.   It  is  seen  that, in the coastal area,  weekends
exceeded the standard  more  frequently  than weekdays while, in the inland

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                                  10
area, the opposite is true.   As reported earlier [5],  the  demarcation  at
which weekdays and weekends  are equally polluted runs  from the  north of
Santa Monica to the east of  Anaheim via the Los Angeles  CBD.
     The regionwide weekday/weekend effect on population exposure to Ox
is summarized in Table 2.  Indeed daily maximum concentration of QX were
higher on weekends at some coastal stations.  However, Table 2  shows
that the population in the study region on the whole receives a fewer  per-
cent of both days and hours  exceeding the standard on  weekends  than week-
days .
                 Table  2.   Regionwide  Impact of Weekday/Weekend Effect
                           on  Population Exposure to QX and N02 in 1973
                        Average
                 Percent of Days Exceeded
        Average
Percent of Hours Exceeded

Weekday
Weekend
Weekday/Weekend
Difference
V
30.1
28.6
+1.5
N02
4.4
2.1
+2.3
x
6.31
5.77
+0.54
N02
0.57
0.18
+0.39
  5.1.2  Weekday/Weekend Difference  in  N02
       Isopleths  describing  the  percentage  of  days the N02 California one-
  hour standard is  exceeded  are  shown in  Figure  11.   Figure  12  shows iso-
  pleths of the average duration in  hours for  those  days  on  which  the
  standard was exceeded.  The highest percent  of days exceeding the stan-
  dard is found in  the areas around  the Los Angeles  CBD  and  the lowest
  percent is found  in the fringe areas.

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                               11
     The spatial distribution of the frequency of N02 short-term violations



is quite similar to that of population density and of employment density



shown in Figures 4 and 5 respectively, in contrast to the spatial  distri-



bution of the frequency of 0  short-term violations whose isopleths run
                            A


approximately parallel to the coast line.  The longest average duration



for N02 is found in Orange County.   The spatial  distributions  of the daily



frequency of violation and of average duration in hours  for  NO^ differ from



those for 0 .
           A



     Figure 13 presents differences in daily NOp frequency of violation



during weekdays and weekends.  It shows that in most of the study region



the N02 air pollution is less intense on weekends than weekdays, although



in Orange county weekends are more polluted than weekdays.  From Table 2,



we can see that regionwide N02 air pollution is definitely lower on week-



ends than weekdays.



5.2  EFFECTS OF DAILY POPULATION MOBILITY ON POPULATION EXPOSURE



     Daily population mobility was incorporated into the analysis of pop-



ulation exposure to photochemical air pollution in the Los Angeles Basin.



The working population is considered to be the mobile portion of the total



population.  The effects of population mobility are examined by accounting



for the difference in exposures for the working population while at their



residence compared with exposure at their place of employment during



working time (weekdays, 7 A.M. - 6 P.M.).



     Figure 14 shows that during daytime workers move from their residence



areas  (where the highest Ov concentrations as well as the lowest Ov concen-
                          A                                       A


trations occur) to the business districts (where 0  concentrations are
                                                  A

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                                12
about average).   As a result of this  population mobility, workers  incur

on the average 8% fewer violations  above the  Ox NAAQS  at  their  place  of

employment (Table 3).  In contrast  to this, workers  primarily move from

residential areas of lower N02 concentrations to  business districts of

higher NCL concentrations.  This means that workers  are located in areas

which experience 16% more frequent violations of  the California NO,, stan-

dard.  Thus, the mobility effect is more prounced for N02 (Table 3).

     The regionwide impacts of considering mobility on population expo-

sure for 0  and N0? are summarized in Table 3.  Table 3 presents the
          /^       ^
average percentage of time that people in the region are exposed to a

concentration above the standard.  The mobile population assumption yields

a  lower percentage of hours exceeded for GX than the static population

assumption, while for N02 the  opposite is true.   Since workers constitute

only about 40 percent of  the total population, the effects of population

mobility are  less  pronounced when  considered  for the total population.
          Table 3.
Effect of Population Mobility Consideration on the
Population-at-Risk Indices of All Workers and Total
Population (Percent of Hours Exceeded)

Static Population
Dynamic Population
x
All
Workers
6.03
5.57
Total
Population
6.16
5.96
N0?
All *
Workers
0.48
0.57
Total
Population
0.46
0.50

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                              13
            6.    TRENDS IN AIR QUALITY  AND IN  POPULATION  EXPOSURE

     Trend analyses of the N09 and 0 exposure of the  total  population
                             L-      X
are based on the static population assumption  rather than the  daily  mo-
bile population analysis.   The static population assumption  should intro-
duce very little error while yielding great savings  in computational
effort.  It should be noted, however, that the data  used  for the trend
analysis do reflect the year-to-year changes in the  population distribu-
tion.
6.1  TEN-YEAR TREND FOR 0
                          A
     Isopleth maps depicting percent of days the NAAQS for QX is exceeded
during the five two-year periods, 1965/66, 67/68, 69/70,  71/72, and
73/74 are shown in Figure 15.  In 1965/66 more than  half of the study
region violated the standard on more than 50% of the days and the rest
of the region at least 20% of the days.  In 1973/74, the area in vio'ie^.ion
at least 180 days per year decreased to a small area around Azusa, and an
area in which the standard was violated less than 20% of the days appealed
in the southern half of the region.
     The isopleth maps of average number of hours per day above the NAAQS
on days in violation in the five two-year periods are shown in Figure 16.
In 1965/66, the inland areas had an average duration longer than six hours
per  day and the coastal areas longer than three hours per day.  In 1973/74,
the  average durations decreased compared to those in 1965/66 but were
slightly above the average duration in 1971/1972.
     Figure 17 depicts the improvements in  population exposure to QX over
the  10-year period.  Each  vertical  bar indicates  the percentages  of the

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                              14
population who were exposed to a concentration above the NAAQS for various

percentages of days.  For example, in the first set of bars, about 53% of

the population were exposed to 1-hour 0  above the NAAQS more than 50% of
                                       A

the days in 1965/1966.   In 1973/74,  the percentage of the population with

the same exposure dropped to less than 5%.   The second group of vertical

bars is prepared for oxidant exceeding a level twice as high as the standard,

while the third group is for three times the NAAQS.

     The regionwide trends in population exposure to 0  are summarized in
                                                      J\

Table 4.  On  the average, people in the study region were exposed to a

1-hour concentration above the NAAQS 176 days in 1965/66, 144 days per
year  in  1969/70, and  105 days per year in 1973/74.  The average duration of

such  exposure also decreased from 5.1 hours per day in 1965/66 to 4.6 hours

per day  in  1969/70, and to 4.3 hours per day in 1973/74.  The trends are

similar  for concentrations exceeding twice the standard.

      Table  4.  Regionwide Trend in Average No. of Days NAAQS for 0  was
               Exceeded and the Average Duration of Excess Air Pollution
               in Hours per De
Threshold
0 NAAQS
160 yg/m3
(8 pphm)
2X Ox NAAQS
320 pg/m3
(16 pphm)

Average # Bays
Per Year
Avg. Duration
Average # Days
Per Year
Avg. Duration
1965/66
176
5.1
70
3.1
1967/68
162
4.8
59
3.1
1969/70
144
4.6
45
2.8
1971/72
109
3.8
26
2.1
1973/74
105
4.3
26
2.9

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                                  15
  6.2  TEN-YEAR TREND FOR NOg
     The N02 trends in both  the annual  mean concentrations  and the  99th
percentile concentrations are shown in  Figure 18.   The  vertical  bar indicates
the range of values about the average and 99th percentile of one hour concen-
trations observed at the 8 monitoring stations.  Although there is  no obvious
trend in both the annual mean concentrations and the 99th percentile concen-
trations, the range of individual  station values decreases  steadily after
1967/68.
     Isopleth maps of annual mean N02 concentration are shown in Figure 19.
Almost everywhere over the study region the national air quality standard
         o
(100 yg/m ) was violated during the entire 10-year period.   However, an air
quality  improvement during the later part of the study period can be detected.
For example, during the 1967/68, 69/70, and 71/72  periods,  N02 concentration
                           3
levels higher than 130 yg/m  covered the majority  of the heavily populated
areas, while in 1973/74 those levels were confined to the San Fernando Valley.
         Figure 20 depicts the percentages of the population exposed to var ous
levels of annual mean N02 concentration.  For example, the  percent of the pop-
                           o
ulation  exposed to 130 yg/m  or higher  changed from 19% in  1965/66 to 65% in
1969/70, and then back to 33% in 1973/74, indicating a mixed trend in popula-
tion exposure to NO,,.  There is a slight degradation at low levels of exposure.
Virtually everyone in the study area was exposed to annual  average N02 over
the national standard after 1969.

-------
                                  16
     Isopleth maps of the percentage of days  exceeding  the  California  one-
                       2
hour standard (470 yg/m ), as shown in Figure 21,  again indicate  a  mixed
trend.   The area exceeding the standard more  frequently than  6% of  the days
was approximately matched with the area of Los Angeles  city in 1965/66, ex-
tended to almost the entire study region in 1967/68,  69/70, and 71/72, and
was drastically reduced in 1973/74.
     The isopleth maps of the average number of hours exceeding the California
one-hour standard per day on days in violation are shown in Figure  22.  The
area with an average duration longer than three hours per day was confined  to
the north-central part of the San Fernando Valley in  1965/66, extended to the
majority of the study region in 1967/68, 69/70, and 71/72,  and shrank  to the
Los Angeles downtown area in 1973/74.
     Figure 23 shows the percentages of the population exposed to N02  con-
centrations above the California one-hour standard.  For example, in 1965/66
9% of the total population was exposed to excessive concentrations on more than
44 days  C\z%  x  365)  per year, while in 1973/74 none of the population was ex-
posed that  often.
     The regionwide  trends in population exposure to N02 are summarized in
Table 5.  On  the average people in the study region were exposed to a 1-hour
NOp  concentration  above the California standard 25 days per year in 1965/66,
27 days  per year in  1969/70, and 18 days per year in 19/3/74.  The average
duration of such exposure changed from 2.6 hours per day in 1965/66 to 3.0
hours per day in 1969/70, and to 2.5 hours per day in 1973/74.

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                                  17
Table 5.  Regionwide Trend in Average No.  of Days Per Year the California
          Standard for NO- was Exceeded and the Average Duration  of Viola-
          tions in Hours per Day
Threshold
CA. N02 STD
470 yg/m3
(25 pphm)
Index
Average # Days
E-xeeeded/Year
Avg. Duration
1965/66
25

2.6
1967/68
40

3.3
1969/70
27

3.0
T97T/72"
33

3.0
1973/74
18

2.5

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                                  18
                           7.    REFERENCES
1.   Zupan, J.  M., "The Distribution  of Air Quality in the New York
    Region," Resources for the  Future, Inc., Wash. D.C., 1973.

2.   Horie, Y.  and A.  C. Stern,  "Analysis  of Population Exposure to
    Air Pollution in  the New York-New Jersey-Connecticut Tri-State
    Region," U.S. EPA Publication  No. EPA-450/3-76-027, March 1976.

3.   California Air Resources Board,  "Ten-Year  Summary of California
    Air Quality Data  1963-1972," State ot California, The Resources
    Agency, January 1974.

4.   Elkus, B., and K. R. Wilson, "Air Basin Pollution Response Func-
    tion:  The Weekend Effect," University of  Calif., San Diego,  1976.

5.   California Air Resources Board,  "Weekend Oxidant Concentrations,"
    in California Air Quality Data,  6(2)  p. 5, July-Sept.,  1974.

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                                  17
Table 5.  Regionwide Trend in Average No.  of Days Per Year the California
          Standard for NOp was Exceeded and the Average Duration of Viola-
          tions in Hours per Day
Threshold
CA. N02 STD
470 yg/m3
(25 pphtn)
Index
Average # Days
E-xceeded/Year
Avg. Duration
1965/66
25
2.6
1967/68
40
3.3
1969/70
27
3.0
1971/72
33
3.0
1973/74
18
2.5

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                                  18
                           7.    REFERENCES
1.  Zupan, J.  M., "The Distribution  of Air  Quality  in  the New York
    Region," Resources for the Future, Inc.,  Wash.  D.C., 1973.

2.  Horie, Y.  and A.  C. Stern, "Analysis  of Population Exposure  to
    Air Pollution in  the New York-New Jersey-Connecticut Tri-State
    Region," U.S. EPA Publication  No.  EPA-450/3-76-027, March 1976.

3.  California Air Resources Board,  "Ten-Year Summary  of California
    Air Quality Data  1963-1972," State ot California,  The Resources
    Agency, January 1974.

4.  Elkus, B., and K. R. Wilson, "Air Basin Pollution  Response Func-
    tion:  The Weekend Effect," University  of Calif.,  San Diego.  1976.

5.  California Air Resources Board,  "Weekend  Oxidant Concentrations,"
    in California Air Quality Data.  6(2)  p. 5, July-Sept.,  1974.

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                                                                                  San Bernardino


                                                                                  County
               Miles


         Trend  Analysis for Ov
         1973 Analysis       x
 	   County Boundary
 	AQCR

///////   Trend  Analysis for NO
                                                                                                     i	.
                             Figure 1.  BOUNDARIES SHOWING TREND ANALYSIS AREA, 1973
                                             r- AREA> nND LOS ANGELES AQCR.

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I
                                                                           TREND ANALYSIS
                                                                      o+  1973 ANALYSIS
                       \
                       \     LOS ANGELES COUNTY
                        \
      VENTURA COUNTY
                                 4
                           \     O
                            \
                             'i

                            r1    i
                                              10
                                              o
 1. Ojai
 2. Camarillo
 3. Point Mugu
 4. Newhall
 5. Reseda
 6. West L.A.
 7. Lennox
 8. Burbank
 9. Los Angeles
10. Pasadena
11. Long Beach
12. Azusa
13. Whittier
                14.  La Habra
                15.  Anaheim
                16.  Costa Mesa
                17.  Pomona
                18.  Chino
                19.  El Toro
                20.  Upland-ARB
                21.  Upland
                22.  Norco
                23.  Riverside
                24.  Riverside
                25.  San Bernardino
                26.  Redlands
                                                                  u
                SAN BERNARDINO COUNTY
                        25

                .020     *          26
                 	'	1	i
                      O23
             T  22   O24
             _.i   o
                                                                                                                       ro
                                                                                                                       O
  
ORANGE COUNTY
              v
RIVERSIDE COUNTY

                                      Figure 2.    LOCATION  OF MONITORING  STATIONS

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                                                                                           K>
Figure 3.   TOPOGRAPHICAL FEATURES OF THE  LOS ANGELES  BASIN.

-------
                                                                            100-1 ,000




                                                                          1,000 - 10,000



                                                                               > 10,000
LOS ANGELES AIR BASIN
                    Figure 4.      POPULATION DENSITY IN PERSONS PER SQUARE MILE  IN 1970.

-------
1
 CD
 CD
 m
 o
 Tl

 -a
 OO
 c/
 -o
 i
 O
 m
 o
 on
 XD
 c:
 I

 O

-------
LOS ANGELES AIR BASIN
                         Figure 6.     PERCENT CHANGE  IN POPULATION  1965 TO 1975.

-------
                                                                          < 0
0	5   10
      miles




 LOS ANGELES AIR BASIN
                      Figure 7.   PERCENT CHANGE  IN EMPLOYMENT FROM 1965  TO 1975.

-------
                                                                                                             ro
                                                                                                             CT1
Figure 8.  ISOPLETHS OF PERCENT OF DAYS ON WHICH THE NAAQS FOR OXIDANT WAS EXCEEDED  IN 1973.

-------
Figure 9.  ISOPLETHS OF AVERAGE  DURATION  (HOURS) ON  DAYS  WHEN THE NAAQS  FOR OXIDANT
           WAS EXCEEDED IN  1973.

-------
                                                                                                           ro
                                                                                                          lea
Fiaure 10   THE  DIFFERENCE IN PERCENT OF THE NUMBER OF DAYS  ON WHICH THE NAAQS FOR OXIDANT
FngurelO.  t  j"'": ^ Ig73> WEEKDAy MINU$ WEEKEND.   (DARK LINE EQUALS ZERO PERCENT.)

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Figure 11 .   ISOPLETHS  OF  PERCENT OF  DAYS ON  WHICH THE  CALIFORNIA ONE HOUR  STANDARD  FOR N02
            WAS EXCEEDED  IN  1973.

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                                                                                                              co
                                                                                                              o
Figure 12.  ISOPLETHS OF AVERAGE DURATION  (HOURS) ON DAYS WHEN THE CALIFORNIA ONE HOUR  STANDARD

            FOR N02 WAS EXCEEDED IN 1973.

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Figure 13.   THE DIFITRENCE  IN PERCENT OF THE NUMBER OF DAYS ON WHICH THE CALIFORNIA ONE HOUR
            STANDARD  FOR NO, WAS EXCEEDED IN 1973, WEEKDAY MINUS WEEKEND.   (DARK LINE EQUALS
            ZLRO PERCENT.)  L

-------
                                                       WORKERS PER SQUARE MILE
Ficmre 14   THE NET INFLUX OF POPULATION  (WORKERS)  DURING WORKING TIME  IN
         '   PERSONS PER SQUARE MILE  IN  1970

-------
1965/1966
1967/1968
 1969/1970
                                                                 1971/1972
                                                                 1973/1974
                         Fiqure  15  PERCENT OF  DAYS ON WHICH THE NAAQS
                                   '  FOR OXIDANT WAS EXCEEDED DURING
                                     FIVE 2-YEAR PERIODS.
                                                    < 20%

                                                 20 - 50%

                                                    > 50%

-------
 1965/1966
1967/1968
                                                                   1971/1972
                                                                  1973/1974
                          Figure 16. AVERAGE DURATION  (HOURS) ON DAYS
                                     WHEN  THE NAAQS FOR OXIDANT WAS
                                     EXCEEDED DURING FIVE 2-YEAR PERIODS,
                                                    < 3 HRS

                                                  3 - 5 HRS

                                                    > 5 HRS

-------
VD  00  O
                                                             P IN PERCENT


                                                                     P < 5

                                                                  5  P < 10

                                                                 10  P < 20

                                                                 20  <_ P < 50

                                                                 50  < P
                                                           Example:   In  1965/1966  about 53%  of  the
                                                             total  population  was  exposed  to U3
                                                             leves above the  NAAQS (8 pphm  for one
                                                             hour)  more  than 50% of the days per year
                                                             In the same period about 44*  of the total
                                                             population  was exposed to 03  levels at
                                                             twice the NAAQS for at least  20^ of the
                                                             days per year, but less than  50/0 of the
                                                             days per year.
                                                                                                    OJ
                                                                                                    CJ1
                                              3 x standard
1  x standard           2 x standard


 Figure  17.  CHANGES IN POPULATION EXPOSURE TO ^ DURING FIVE 2-YEAR PERIODS.

-------
                                              36
               30  -
CALIFORNIA 1-HR
    STANDARD    ,
25pphm = 470yg/m':
               20  ~
                                                         -
                                                          600
                                                         -500
                                            -1-     o
                                     -400
                                                         -300
         o.
         D.
          00
         O
                10  -
 EPA STANDARD
 ANNUAL  AVERAGE
 100yg/ni3 =  5.3pphm
>
I    t    *
                                            I
.200


 -150


 TOO


 . 50
                                               en
                                               3.
                                                CM
                                               O
                        	!	,	,	1      i	
                         65/66 67/68 69/70 71/72 73/74
        Figure 18.,   THE AVERAGE VALUE AND THE RANGE OF VALUES FOR EIGHT MONITORING
                     STATIONS SHOWING N02 TRENDS IN ANNUAL MEAN CONCENTRATIONS (LOWER
                     SEGMENT) AND IN 99th PERCENTILE CONCENTRATIONS'(UPPER SEGMENT).

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1965/1966

                      r~
1967/1968
                                                                   1973/1974
                            Figure 19.  N02 ANNUAL MEAN  CONCENTRATION
                                         (yg/rri  )  FOR FIVE  2-YEAR  PERIODS.



                                                                   _3
 1969/1970
                                                        <  TOO yg/m"
                                                   100 - 130  yg/m'
                                                         >  130 yg/rrT
 1971/1972




	I

-------
i.o r
N02 ANNUAL MEAN I
         in yg/nr
ONCENTRATION
                                                [N02]  <  TOO

                                                100 <_  [N02]  <  130

                                                130 <  [N02]
                                           Example:   During  1965/66 about 91% of the  population
                                               was  exposed to N0 concentration  between  100  and
                                               130  yg/iA   About 19% were exposed to  N02 concen-
                                               trations above 130 ug/m3.   The NAAQS  is  100 yg/nr3
                                               annual  average.
                                                                                                      00
   Figure 20. CHANGES IN THE TOTAL POPULATION EXPOSURE TO N02 DURING FIVE 2-YEAR PERIODS.

-------
                                           1965/1966
                                                                                                         1971/1972
                                        1969/1970
L	
                                                                                                        1973/1974
                                                                   Figure  21   PERCENT OF DAYS ON  WHICH THE
                                                                             '  CALIFORNIA 1-HR STANDARD FOR N02
                                                                               WAS  EXCEEDED DURING FIVE 2-YEAR
                                                                               PERIODS.
                                                                                          < 6%

                                                                                        6-12%

                                                                                          > 12%

-------
1965/1966
1967/1968
                                                                 1971/1972
                                                                  1973/1974
                          Figure 22.    AVERAGE DURATION (HOURS) ON DAYS
                                        STANDARD WAS EXCEEDED DURING
                                        FIVE 2-YEAR PERIODS.
                                                     < 2 MRS


                                                   2 - 3 HRS


                                                     > 3 HRS
                                                                                   P-
                                                                                   O
 1969/1970

-------
                            PERCENT OF  TOTAL POPULATION
ro
GO
o
 X
 -o
 o
 oo
 o

 z
 o
 o
 c:
ro
i

m

70

-o
m
70
*-H
o
o
                                                                           o
                                                                           f*
                                                                           73
                                                                           O

                                                                           m
                                                                           x
                                                                           o

-------
                               A-l
           APPENDIX  A .   SUMMARY  OF AIR  QUALITY  DATA OBSERVED
                          AT MONITORING STATIONS
Table Al.   Percent of Days the NAAQS for 0  was  Exceeded and  the
                                          X
           Average Duration in Hours (x.x) in 1973.
Table A2.   Percent of Days the California Standard for N02 was
           Exceeded and the Average Duration in  Hours (x.x) in
           1973.
Table A3.   Percent of Days the NAAQS for 0  was  Exceeded and the
                                          A
           Average Duration in Hours (x.x) for Each of the Five
           2-Year Periods.
Table A4.  Percent of Days the California Standard for N02 was
           Exceeded and the Average Duration in Hours (x.x) for
           Each of the Five 2-Year Periods.
Table A5.  Annual Arithmetic Mean Concentrations for N02 in Each
           of  the Five 2-Year Periods.

-------
CVJ
a:
                                     (17*9
u'e

(9*9
(9'f

(S'fr
(1*9
('17
C9*<7
(8*t7

(l-9
(9*9
(S'S
(f7|S

(9*f7

C6'2
                                             0*6?
                                             9S
                                             S'frfr
                                             &S
                                             0'
                                             l*Z?
                                             *
                                            o's?
                                            0q?
                                            0*17 f?
                                            0*t7t7
                                            SM
                                            9T
                                            *ST
                                            O'S?
                                            OM?
 fO'9
 (1*8
 Cfr!
 (9*5
 (5*9
 (S*f7
(i*9
('f7
(f!*5
(0*9
(5*4
U'9
(0*i
(5*9
(0*9
(O'f

(O't;
(0*
2*t?q
 J*I7
 I'A?
S'S
O'Ofi
S  fr b
6'
O'i?
^8f
? * S" C
7%
S* IT
<3* I?
17*99
 * rt *_
   T V

0*05
i 4 t. ^~
Ci  O I*
b*/.
8%t
/.*6e
t7*et
                                                                                      if
                                                                                              11 V M f , "--I M
                                       I SIM
v'l

i vru
                                                                                                    7
         I?

         61

         / t
T
0
b
P
Z
        n
        i
                                                                                                  V I S
                    SVM
                                                             M
                                                             xn
                            (X*X) SrtOfjM  Nil
                           jo
                                                                                                   t*

-------
UtfLE  A*.
    *AS t
 1
 d
 3
 a
 b
 to
 7
 6
 9
10
1 I
12
li

15
lo
17
18

20
                 T  IJF  OAV5 THE CALIFORNIA STANDARD F OK  N02
                  A\f,  T^t  AVERAGE  DURATION IN HOOPS (X.X)  IN  197,
      S 1 A i TH-M
      A-~4 An JM
      LA HA^RA
      CU&TA MESA
      Ei, (nun
      SAN  REHNAGIrv.)
      RfcULANOS
      c' H i N Q
      UPLAND,CIV 1C CT*
      UPt-AND-AKij
      UJAI
          MUGU
      AZUbA
      BU^BANK-RALM
      ^ts r LA,^s"
      LUW* BEACH
     w H i r T i E H

     PASADENA-WALNUT
                                     AE.iK*PAY
2,a f 5,0)
3,a ( a.fe)
1,1 ( 1,1)
 .7 ( 1,9)
0,0 ( 0,0)
0,0 ( 0,0)
 .6 ( 1,6)
0,0 ( 0.0)
0.0 f 0,0)
 .7 f 1,9)
 ,9 f 4.0)
,0 ( 0,0)
    ( 0,0)
    ( 0,0)
    C 1,7)
    ( 3.3)
    ( 1.3)
    ( 3.1)

    ( 2 ^)
    f 2!*)
    f 34)
    ( 2)2)
0,0
0,0
t.l
5,7
,3
9,2
.5
6.7
3 4
2J3
6,4
3,4 ( 3.8)
0,0 ( 0,0)
2.8 ( 2.2)
                                                           WEEK-END
                                                                 *
                     6,0
(  1,9)
(  1,7)
(  0,0)
(  0,0)
(  0,0)
(  2.7)
f  0,0)
(  0,0)
(  0,0)
(  0,0)
C  0,0)
(  0,0)
(  0,0)
(  0,0)
1.6
0,0
0,0
0,0
1 ,"5
0,0
0,0
0,0
0,0
o.o
0,0
0,0
0,0
1.0 ( l.)
0,0 ( 0,0)
1.3 C 2,6)
3,3 ( 1.5)
3,5 ( 3,1)
0,0 C 0,0)
0,0 ( 0,0)
0,0 ( 0,0)
4,7 ( 1,9)
0,0
                                                                                                    I
                                                                                                    CO
                                                         0,0
                           0,0)
                           0,0)

-------
TABLE A3, PERCENT o DAYS THE NAAQS FOR ox WAS EXCEEDED AND THE AV
DURATION IN huuS (X,*) f-'UR EACH OF THE Fivt 2-VEAR PERIODS.
NO, STATION 1965/66 lt6|/68 If6*/70
1
8

4
5
6
7
8
9
10
ANAHEJM
A2USA
BURBANK.PAIM
LENNOX
LQNli BEAGH
I, A, DOWNTOWN
PQM1JKIA
RESEDA
SAN BERNADINO
WEST L.A.-WSTWOOD

69U
61.0
27 ,9
22^3
62,1

65,4
4} J
53!3
(7.6)
(6. a)
(3.f)
(3.6)

(6^6)

(6!o)
(5.1 )
IS. 4 (3,8) 25,0
68,7 (7
64.0 (6
25.0 (3
17,0 (2
55.1 (5
6
-------
TA8U A. PCRCfeNT OF DAYS 1 Ht CALIFORNIA 8T
T>fc AVFRAGE DURATIPN IN HIJUWS fX.X) FOR
NO,
1
2
i
4
5


6
STATION
AZUSA
BURBANK-PALM
LENNOX
LONG BEACH
l,A, DOWNTOWN
POMONA
RESEo A
WEST L.A.-WSTWOQD
196S/66
;a (?
7,4 (3
5*0 (2
5.0 C?
U;6 (2
1.3 (1
242 (2
e.d (2
.0)
.&)
.1)
.9)
 $)
.1)
.1)
.7)
ANDARD I
EACH UF
1967/68
. a
19.8
14.4
14.4
fO.9
4 7
5 4
10.*0
(l.T)
(4,5)
(4,3)
(3.4)
(2,1)
(3.0)
(3.6)
(2,4)
!'OR Noa
THE FI
WAS kXCEEDED AND
V 2-YEAR PfcRIQDS,
1*69/70
2.3
16.9
5,5
10.7
7*6
4.6
3.0
7.1
(3.2)
(3.9)
(2.3)
(3.2)
(3,0)
(3,4)
(2.9)
(2.3)
19T1/7J
3.9
11. e
6.1
8.?
14.6
5.9
5.%
10.0
(8.7)
(3.2)
(1,0)

(3,f2)
(1.4)
(2,9)
(2.4)
1973/74
5J
6.1
4.2
5.6
* 
6.1
2.1

8.*3
(2.1)
(2.0)
(2.1)
(1 .6)
(3.3)
(2.4)
( 1 ,8)
(2,4)

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TABLE A5.  ANNUAL ARITHMETIC MEAN CONCENTRATIONS FOR N02
    IN EACH OF THE FIVE 2-YEAR
NO.
STATION
1965/66
1967/69
1969/70
1971/72
1973/74
1
I
I
4
*
6
7
8
AZUSA
BURBANK*PAlM
LENNOX
LONG BEACH
L.A, OOrtNTQWN
POMONA
RESEDA
WEST L.A,*WSTWOOD
.5
6,90
6. IS
5.90
7. as
6. SO
5,00
6.10
a. so
9.80
7.50
7.90
6.65
7,45
6.15
6.65
*,70
9,40
6.75
7,70
7,00
8,05
6.95
6.55
6,eo
8.5b
6.65
6,5
8,45
7.75
7.00
6.90
6,2k
7,25
6.19
6,75
7,05
7,05
6.05
7,05

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                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing)
1. REPORT NO.
  EPA-450/3-77-004a
                              2.
                                                           3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
  Population Exposure  to  Oxidants and Nitrogen  Dioxide
  in Los Angeles Volume  I:   Executive Summary
             5. REPORT DATE
               January 1977
             6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
  Yuji  Horie, Anton S.  Chaplin, Neil H. Frank,  and
  William F. Hunt, Jr.
                                                           8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
  U.S.  Environmental  Protection Agency
  Office of Air and Waste Management
  Office of Air Quality  Planning and Standards
  Research Triangle Park, North Carolina   27711
             10. PROGRAM ELEMENT NO.
               2AF643
             11. CONTRACT/GRANT NO.
               68-02-2318
 12. SPONSORING AGENCY NAME AND ADDRESS
  Technology Service  Corporation
  2811 Wilshire Boulevard
  Santa Monica, California   90403
             13. TYPE OF REPORT AND PERIOD COVERED
               contract,  re
             14. SPONSORING AGENCY CODE
 15. SUPPLEMENTARY NOTES
 16. ABSTRACT
       A new methodology  was developed to characterize population  exposure to air
  pollution and was applied to the analyses  of two photochemical pollutants in the
  Los Angeles Basin --  Ox and NO?.
       An analysis was  made on the 1973 air  quality and population data to examine
  the weekend effect  and  the population mobility effect on population exposure to
  these two pollutants.
       The methodology  was applied to the air quality and population data for the
  five 2-year periods from 1965/66 to 1973/74 to determine the  trends in air quality
  and in population exposure to Ox and N0.
       The important  results of the study are described in the  section called
  "Highlights" presented  as a preface to this report.
17.
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS  C.  COS AT I Field/Group
  Photochemical Air  Pollution
  Air Quality Monitoring
  Population Exposure
  Data Analysis
  Air Quality Trend
18. DISTRIBUTION STATEMENT
                                              19. SECURITY CLASS (ThisReport)
                                              	Unclassified
                                                                          21. NO. OF PAGES
                                 61
        Unlimited
20. SECURITY CLASS (Thispage)
       Unclassified
                                                                         22. PRICE
EPA Form 2220-1 (9-73)

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