United States Environmental Protection Agency Air and Energy Engineering Research Laboratory Research Triangle Park, NC 27711 Research and Development EPA/600/SR-93/019 March 1993 &EPA Project Summary Characterization of PM-10 Emissions from Antiskid Materials Applied To Ice and Snow-Covered Roadways John S. Kinsey Several areas of the U.S. in violation of the National Ambient Air Quality Standard for PM-10 (participate matter with diameters < 10 IJJTI) have conducted studies that have Identified the resus- pension of antiskid material applied to paved roadways as an important source of PM-10. The application of antiskid materials creates a temporary but sub- stantial increase in the amount of fine part leu late on the road surface over and above that which Is normally present. Measured emission data are lacking for all types of antiskid materi- als; therefore, an appropriate field pro- gram whose objective was to establish a predictive model for PM-10 emissions was undertaken. A source-oriented emissions sampling procedure was conducted on a section of US 53 just west of Duluth, MN, during March/April of 1992. The measured emission fac- tors varied from 1 to 11 g/VKT (vehicle kilometer traveled) for the three tests conducted. The data were not sufficient, however, to develop any specific cor- relation between the measured emis- sion factors and source parameters. The only general observation made was PM-10 emissions appear to increase with the amount of antiskid material applied. A comparison of measured emission factors with those predicted by an EPA compilation of air pollutant emission factors (AP-42) indicated that most of the measured factors are higher than those that would be predicted from silt-loading values alone. Due to the marginal test conditions during storms, no definitive assessment of this in- crease can be made until additional data are obtained. This Project Summary was devel- oped by EPA's Air and Energy Engi- neering Research Laboratory, Research Triangle Park, NC, to announce key find- Ings of the research project that Is fully documented In a separate report of the same title (see Project Report ordering Information at back). Introduction Several areas of the U.S. in violation of the National Ambient Air Quality Standard (NAAQS) for PM-10 (airborne particles <10 u,m in diameter) have conducted studies to determine the sources of these emis- sions. One source of PM-10 emissions identified in these studies is the resuspension of antiskid material applied to paved roadways. Antiskid materials may consist of abrasives (e. g., sand, stone, or cinders applied to the road surface to im- prove traction) or deicers, which restore pavement traction by preventing the for- mation of ice films, weakening the ice/ pavement bond, and/or by melting ice and snow. The application of antiskid materials cre- ates a temporary but substantial increase in the amount of fine particles on the road surface over and above that which is nor- mally present. Prior research has estab- lished a direct relationship between the loading of silt-size fines (particles < 75 \im in physical diameter) and the PM-10 emis- sion generated by vehicular traffic. "The empirical relationship between silt loading and PM-10 emissions is reflected in EPA- Printed on Recycled Paper ------- recommended PM-10 emission factors for paved urban roads. In a recent EPA study, a literature search, an engineering analysis, and a laboratory testing program were performed to provide air pollution control agencies with information on how to identify an ap- propriate antiskid material that is both du- rable and effective and produces lower PM-10 emissions. The primary objectives of this study were to provide guidance on methods to determine (a) the physical properties and durability of antiskid mate- rials selected for use on ice- and snow- covered roadways, and (b) criteria for defining the elements of an effective PM- 10 emission control strategy associated with use of antiskid materials. Although the above study provided guid- ance for the selection of antiskid materi- als, no direct information was developed regarding the actual PM-10 emissions re- lated to their use, the changes in surface silt loading resulting from such applica- tion, or the degree of control actually achieved by compliance with the material selection criteria developed in the study. Measured emissions data are lacking for all types of antiskid material, but deicing chemicals have received the least amount of attention. Therefore, an appropriate field program was needed to establish a suit- able method for predicting PM-10 emis- sions from the use of antiskid materials. This is the primary objective of the work reported here. Source-oriented emissions sampling was employed in the program using Mid- west Research Institute's (MRI's) "expo- sure profiling" approach. The data obtained by this technique were coupled with the results of road surface sampling and ma- terials application data in an attempt to develop a method for predicting PM-10 emissions. Site Selection The original test site was located on northbound US 53 at Mile Post (MP) 13.35 (or approximately Station No. 452+50). This particular location has good orienta- tion with respect to the wind direction an- ticipated for periods after storms, good exposure to ambient winds (i.e., lack of trees in the upwind direction), and a rela- tively flat median for installation of the air- sampling equipment. However, due to the mild winter in Duluth, the original test site could not be used. The site was selected on the assumption that the ground would remain frozen throughout the sampling period, allowing equipment to be safely placed on the median. When the ground remained thawed, the sampling site was moved approximately 1/4 mi (0.4 km) northbound (i.e., to the west) to an area near the intersection of US 53 with a county road. This area provided a firm surface for the sampling equipment but had a substantial stand of trees bordering the northern portion of the right-of-way which did not conform to criteria estab- lished by MRI for exposure profiling. For this and other related reasons, only one of the three test series was conducted under suitable conditions with respect to wind speed and direction. This noncom- pliance with established criteria adversely affected data quality as discussed below. Overall Study Design The source-directed field sampling con- ducted in this study employed the expo- sure profiling approach to quantify source emission contributions. The exposure pro- filing technique for particulate source test- ing is based on the isokinetic profiling concept used in conventional (stack) test- ing. The passage of airborne pollutant im- mediately downwind of the source is measured directly by means of simulta- neous multipoint sampling over the effec- tive cross section of the dust source plume. This technique uses a mass flux mea- surement scheme similar to EPA Method 5 stack testing rather than requiring indi- rect emission rate calculation through the application of a generalized atmospheric dispersion model. Air Sampling Equipment For measurement of particulate emis- sions from the test road, a vertical net- work of samplers (Table 1) was positioned 5 m downwind and 10 m upwind from the edge of the pavement. Four downwind vertical sampling arrays (D1 through D4) and two vertical upwind arrays were used. Three of the downwind arrays (D1, D3, and D4) and one upwind array (U2) made use of high-volume (hi-vol) air samplers equipped with constant-flow electronic con- trollers and cyclone pre-separators. The remaining two arrays (D2 and U1) used hi-vols equipped with Wedding PM-10 in- lets and critical orifice flow controllers. Testing Procedures Prior to actual sample collection, a num- ber of decisions were made as to the potential for acceptable source-testing con- ditions. These decisions were based on forecast information obtained either from the local U.S. Weather Service office and/ or from the Roadway Weather Information System (RWIS) located at the site. If con- ditions were considered acceptable, the sampling equipment was prepared for test- ing. Pretest preparations included calibra- tion of the various air sampling instruments and insertion of filters. All sampling activi- ties followed quality control (QC) proce- dures approved by EPA prior to testing. The particulate samples were collected on Type AH grade glass fiber filters. The filters were analyzed gravimetrically at a constant temperature and humidity in a Table 1. Sampler Deployment Sampler array ID -j-j~ U1 U2 D1, D3, D4 D4 D4 D2 ' Certain downwind sat No. of instruments 1 2 4 2 1 1 mnlinn Ofininmont muM nnt K Measurement height(s) (m) —3 1.5,3 1, 3, 5, 7 1,5 3 2.5 Type of sampler or instrument Hi-vol + Wedding inlet Hi-vol + Cyclone Hi-vol + Cyclone Warm wire anemometer Wind vane Hi-vol + Wedding inlet Parameter(s) measured PM-10, Pb PM-10 PM-10, Na+,CI (Selected arrays only) Wind velocity Wind direction PM-10, Pb ------- special laboratory. Selected filters were also extracted and chemically analyzed by an independent laboratory to deter- mine the concentration of chloride (Cr), sodium (Na*), or lead (Pb) in the particu- late sample collected. Appropriate quality assurance/quality control (QA/QC) proce- dures were used throughout all sample analyses. Ancillary Sampling and Analysis The types of ancillary samples and in- formation collected in the program fall into two broad categories: antiskid materials and roadway surface samples, and source activity levels. Each is described below. In conjunction with the emissions tests, samples were taken of the antiskid mate- rial (abrasive/rock salt mix and straight rock salt) applied to the road and the dust remaining on the surface after it dried. These samples were needed not only to evaluate the performance of existing emis- sion models but also to develop improved models for antiskid materials. Antiskid samples were analyzed for silt and mois- ture content as well as a number of key physical and chemical properties thought to be important in the generation of silt loading (e. g., mass of material < 75 u,m in physical diameter) on the road surface. Road surface samples were analyzed for silt content using established MRI proce- dures. Source extent and activity data were collected with a variety of tools. For ex- ample, in addition to visual observation and note taking, pneumatic traffic counters were used to determine source activity on US 53. A radar gun was used to deter- mine the average speed of vehicles pass- ing the sampler array. In conjunction with the program, de- tailed information was collected indepen- dently by the Minnesota Department of Transportation (MNDOT) on the condition of the weather and pavement during the course of the storm, the types and amounts of antiskid materials applied to the test road, and a general indication of the re- sidual deicing chemical on the road sur- face at various times. These data were used to augment the information obtained on source activity mentioned above. Addi- tional surface sampling was conducted between storms to develop a silt-loading "history" during data analysis. Calculation Procedure To calculate emission rates from the measured PM-10 concentrations (mass/ volume), a conservation of mass approach was used. The passage of airborne par- ticulate (i.e., the quantity of emissions per unit of source activity) was obtained by spatial integration of distributed measure- ments of exposure (mass/area) over the effective cross section of the plume. Ex- posure is the point value of the flux (mass/ area-time) of airborne paniculate integrated over the time of measurement, or equiva- lent ly, the net paniculate mass passing through a unit area normal to the mean wind direction during the test. To be con- sistent with the NAAQS, all concentra- tions and flow rates were expressed in standard conditions (25°C and 101 kPa or 77°F and 29.92 in. Hg). Field Sampling Program Source Description and Activity The test site used in the experimental program was located on northbound US 53 on the outskirts of metropolitan Duluth, MN. US 53 is an unlimited-access, four- lane, high-speed roadway carrying com- muter traffic to and from Duluth at an approximate volume of 5,000 vehicles/day. Data collected during field sampling showed that most traffic was two-axle, light-duty vehicles traveling between 88 and 97 km/h (55 and 60 mph). Normal surface loadings, determined both visually and by sampling, were generally very low, with silt loadings in the range of 0.2 g/m2. Exposure profiling was performed after two minor storms that occurred on April 10, and on April 21 and 22, 1992. One test series was conducted on April 11, with additional testing on April 23 and 26. During the April 10 storm, approximately 4 to 6 in. (10 to 15 cm) of wet snow fell on US 53 in 24 h. Four applications of an abrasive/salt mixture were made to the northbound lanes over a period of ap- proximately 10 h totaling 395 kg/lane-km (1,400 Ib/lane-mi). During the second storm, a combination of wet snow and freezing rain fell during approximately a 36-h period. In this case, only one appli- cation of 197 kg/lane-km (700 Ib/lane-mi) was made to each lane especially for test purposes. As determined in previous research, the application rates used by MNDOT are far below those of most other transportation agencies. Also, much of the material ap- plied was either cast off by the snow plow during clearing operations or eliminated by melted precipitation. The material that remained on the surface was quickly lost to the atmosphere by the action of pass- ing vehicles. Thus, surface loadings were generally low, with higher loadings ob- served in the passing (left) lane, com- pared to the driving (right) lane. Exposure Profiling Results The results of the three PM-10 expo- sure-profiling tests are shown in Table 2. These results were calculated using the outcome of the gravimetric analyses per- formed to obtain the measured (i.e., blank- corrected) PM-10 concentration at each sampling location. Net (i.e., upwind-cor- rected) PM-10 concentrations were then determined at each vertical sampling height by subtracting estimates from a straight line fit of the measured upwind concentrations. (Note that net concentra- tions were calculated only for arrays with adequate information for integration pur- poses.) Using these net concentrations, the PM-10 exposure was calculated for each measurement location and exposure integration performed using a two-step pro- cess. Finally, PM-10 emission factors were calculated from the data. Results of Chemical Analyses As mentioned above, selected filters (in- cluding blanks) were submitted for chemi- cal analysis for either Pb or Na* and Cr content. The concentration of paniculate Pb was determined both upwind and down- wind of the road during Tests AY-4 and AY-5, using samples collected by the two Wedding PM-10 instruments. (Similar analyses could not be performed for Test AY-3 due to a downwind sample invali- dated by generator problems.) In the case of Na* and Cr, filter sets from one down- wind profiler array for each of the three tests were submitted for chemical analy- sis. The purpose of these analyses was to determine the relative contribution of rock salt to the total PM-10 emissions from the roadway. As shown by the experimental data, the analyte mass found on most of the filters does not exceed the blank values for any of the three species. Of the few filters which show a net increase in analyte mass over the blank value, the quantity deter- mined is generally so slight as to be negli- gible. Therefore, for the purpose of this study, it was assumed that the contribu- tion of both Pb and NaCI to the total PM- 10 emissions from the road was not significant and thus could be ignored. For this reason, no specific emission factors were developed for either Pb or NaCI in the current program. Results of Ancillary Sampling and Analysis Samples of both the abrasive/rock salt mixture and straight rock salt were col- ------- Table 2. Results of Emission Factor Calculations' Run No. AY-3 AY -4 AY-5 Array No. """ f*> J""" D-1 D-4 D-1 D-4 Sampler height (m) 1 3 5 7 1 3 5 7 1 3 5 7 1 3 5 7 NetPM-10 concentration (\ig/std m3)" 26.9 14.5 - 0 79.8 28.8 0 0 31.2 19.6 1 .11 0 20.4 7.8 4.5 3.3 Wind speed (m/s) as (5.4) 6.1 (6.7) 3.9 (5.7) 6.6 (7.3) 0.58 (1.0) 1.2 (1.4) 1.4 (1.7) 1.9 (2.1) NetPM-10 exposure (lig/cm>) 109 83.2 (41.6) 0 338 178 0 0 6.84 7.41 0.50 0 37.7 17.5 11.3 9.14 Integrated No. of exposure vehicle (m-\ig/cm*) c passes 459 1,175 1,038 983 31.8 220 149 650 PM-10 emission factor (gWKT) 3.91 10.6 1.44 2.29 1 Parentheses denote inter/extrapolated values. ~~~ — — — , w^, ~, ™u OUWM «m,u,ai ow ** u»w trm» uo mssn measured oownwina ana upwina concentrations. Upvrind data inter/extrapol "" °'^^^ fmm0to1m ^9*. with Simpson's rule used for integration be^een lected from the MNDOT storage piles and/ or spreader trucks. These samples were then analyzed for moisture and silt con- tent as well as various key material prop- erties. Using the data obtained for the abra- sive/salt mixture, a comparison was made of properties with EPA material selection criteria. This comparison showed that the abrasive/salt mixture used by MNDOT did not meet three out of the four key param- eters thought to be important for high ma- terial durability. For this reason, the abrasive/salt mixture analyzed in the cur- rent program was classified as being of questionable quality, based on the results of previous testing. Road surface sampling was also per- formed throughout the period that field testing was attempted in Duluth, MN. Samples were collected and analyzed to determine silt loading using accepted pro- cedures. Surface samples were collected from both the driving (right) and passing (left) lane on the northbound and southbound sides of the median near the air sampling site with the majority of the sampling performed on the northbound lanes. Using the silt loading data. PM-10 emis- sion factor estimates were calculated for the various samples using the AP-42 pre- dictive model. Emission factors were pre- dicted for both northbound (abrasive/salt mixture) and southbound (rock salt only) lanes in terms of grams per vehicle kilo- meter traveled (g/VKT). As shown in Table 3, predicted emis- sion factors, based on silt-loading data, were generally low, ranging from less than 1 to a maximum of 4 g/VKT. The highest emission factors (resulting from the high- est silt loadings) are for samples collected from the northbound lanes (abrasive/salt mixture) after a fairly major storm on Feb- ruary 24, 1992. (Note that this storm oc- curred priono field testing. After that time, the predicted emissions generally drop to < 1 g/VKT until the next storm in early April. This decrease in loading would be expected due to the effects of traffic, which tends to reestablish a silt-loading "equilib- rium" on the road surface after external influences (e.g., the application of antiskid material) have been eliminated. As also found, the estimated emission factors are of the same approximate magnitude as the test results provided in Table 2 This lends some additional credibility to the data obtained by exposure profiling in the current study. Discussion of Results As shown by the above test results, the measured emission factors varied from 1 to 11 g/VKT for the three tests conducted. The data were not sufficient, however, to develop any specific correlation between the measured emission factors and source parameters such as quantity of antiskid material applied, time since application, and silt loading. The only general obser- vation that can be made from the data is that the PM-10 emissions appear to in- crease with the amount of antiskid mate- rial applied during the two storms tested (i.e., the emission factors for Test AY-3 are higher than for Tests AY-4 and AY-5). (Also note that Test AY-5 had the most acceptable wind conditions of the three tests conducted and thus represents the most reliable emission factor determined in the study.) Otherwise, the results do not seem to follow a consistent relation- ship. A major cause for the lack of asso- ciation was the marginal test conditions discussed above. A comparison of the measured emis- sion factors (Table 2) with those predicted by the current AP-42 equation (Table 3) also yields some interesting results. With only a relatively few exceptions, most of the measured factors are higher than those which would be predicted from silt-loading values alone In the case of the test (i.e., northbound) lanes themselves, the mea- sured factors either equal or exceed the lane average emissions predicted by the AP-42 equation, except for the February 26 samples that were collected after a fairly major storm. This suggests that the application of antiskid material results in a short-term increase in PM-10 emissions from the roadway in an amount greater than that which would be predicted by silt ------- Table 3. Predicted PM- 10 Emission Factors for Measured Surface Silt Loadings • Date 2/26 2X8 3/2 3/11 3/19 4/1 4/22 4/24 Lane sampled NB— Driving NB— Passing SB — Driving SB— Passing NB— Driving NB— Passing SB— Driving SB— Passing NB— Driving NB— Passing SB— Driving SB — Passing NB— Driving NB— Passing SB— Driving SB— Passing NB— Driving NB— Driving * NB— Passing" NB— Driving " NB— Passing * NB— Driving NB — Passing SB-Driving and Passing Road surface silt loading (g/nf) 1.04 0.501 0.529 0.271 0.341 0.0262 0.445 0.295 0.0701 0.0661 0.0382 0.122 0.200 0.164 0.208 0.354 0.0431 0.0788 0.156 0.0618 0.544 0.150 0.133 0.0526 Predicted PM-10 emission factor (g/VKT) 4.10 2.28 2.38 1.39 1.68 0.215 2.08 1.50 0.473 0.452 0.291 0.738 1.10 0.935 1.13 1.73 0.321 0.520 0.900 0.428 2.44 0.870 0.790 0.376 • PM- 10 emission factors predicted using the AP-42 predictive equations and silt-loadings obtained in the program. " Loadings measured after application of antiskid material. loading alone. Although no definitive as- sessment of this increase can be made based on available data, the PM-10 emis- sions could be almost a factor of 3 higher (i.e., 11 vs. 4 g/VKT) than would be pre- dicted from the silt loading. This propor- tional increase in emissions is considerably higher than the precision factor of ap- proximately 2 for the current AP-42 pre- dictive equation and thus worthy of further study. Therefore, a more explicit evalua- tion would help determine the extent of the emissions increase due to the appli- cation of antiskid material to paved road- ways. Conclusions The following conclusions were reached as a result of the current study: 1. Because the measurements con- ducted were performed under diffi- cult environmental conditions that did not meet all of the applicable QC criteria for exposure profiling, data quality was adversely affected. 2. Although the emission factors de- termined in the program ranged from 1 to 1 1 g/VKT for the three tests conducted, these values should be used with extreme cau- tion due to the lack of suitable test conditions during sample collection and resulting poor data quality. 3. The contribution of both particulate Pb and NaCI to the total PM-10 emissions from the road did not appear to be significant based on the limited chemical analyses per- formed during the program. 4. The dry silt loadings determined on US 53 tended to (a) be relatively low and (b) drop off rapidly after a storm, which is typical of high-speed roadways. The amount of silt avail- able for resuspension was also found to be very low due to the minimal application of antiskid ma- terial during the experimental pro- gram. 5. Emission factors determined in the program were generally higher than those predicted by the current AP- 42 equation, based on road sur- face silt loading. The magnitude of this increase could not be defini- tively determined from available data, but it may be almost a factor of 3. •U.S. Government Printing Office: 1993 — 750-071/60218 ------- ------- ------- J. S. Kinsey is with Midwest Research Institute, Kansas City, MO 64110-2299. Charles C. Masseris the EPA Project Officer (see below). The complete report, entitled "Characterization ofPM-10 Emissions from Antiskid Materials Applied To Ice and Snow-Covered Roadways," (Order No. PB93- 150209; Cost: $19.50; subject to change) will be available only from National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at Air and Energy Engineering Research Laboratory U.S. Environmental Protection Agency Research Triangle Park, NC 27711 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati, OH 45268 Official Business Penalty for Private Use $300 BULK RATE POSTAGE & FEES PAID EPA PERMIT No. G-35 EPA/600/SR-93/019 ------- |