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2020 National Emissions Inventory Technical
Support Document: Biogenics -Vegetation and
Soil


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EP A-454/R-23 -001 h
March 2023

2020 National Emissions Inventory Technical Support Document: Biogenics - Vegetation and

Soil

U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Air Quality Assessment Division
Research Triangle Park, NC


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Contents

List of Tables	i

List of Figures	i

8	Biogenics -Vegetation and Soil	8-1

8.1	Biogenics Overview	8-1

8.2	Sources of data	8-1

8.3	EPA-developed estimates	8-1

8.3.1	Continental U.S	8-1

8.3.2	Alaska, Hawaii, Puerto Rico, and Virgin Islands	8-5

8.4	References for biogenics	8-7

List of Tables

Table 8-1: SCCs for biogenic sources	8-1

Table 8-2: Meteorological variables required by BEIS 4	8-3

List of Figures

Figure 8-1: Annual VOC emissions for year 2020 for 12km modeling domain	8-2

Figure 8-2: Normbeis4 data flows for 2020NEI	8-4

Figure 8-3: Tmpbeis4 data flow diagram for 2020NEI	8-5

Figure 8-4: Alaska 9-km modeling domain	8-5

Figure 8-5: Hawaii 9-km modeling domain	8-6

Figure 8-6: Puerto Rico and Virgin Islands 9-km modeling domain	8-7

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8 Biogenics -Vegetation and Soil

8.1 Biogenics Overview

Biogenic emissions are emissions that come from natural sources. They need to be accounted for in
photochemical grid models, as most types are widespread and ubiquitous contributors to background
air chemistry. In the NEI, only the emissions from vegetation and soils are included. Other relevant
sources not included in the NEI are volcanic emissions (geogenic), lightning oxides of nitrogen (NOx), and
sea salt. Biogenic emissions from vegetation and soils are computed using a model that utilizes spatial
information on vegetation, land use and environmental conditions of temperature and solar radiation.
The model inputs are typically horizontally allocated (gridded) data, and the outputs are gridded
biogenic emissions, which can then be speciated and utilized as input to photochemical grid models.

In the 2020 NEI, biogenic emissions are included in the nonpoint data category, in the EIS sector
"Biogenics - Vegetation and Soil." Table 8-1 lists the two source classification codes (SCCs) used in the
2020 NEI that comprise this sector. The level 1 and 2 SCC description for both SCCs is "Natural Sources;
Biogenic" and the full Tier 3 description for both SCCs is "Natural Resources; Biogenic; Vegetation".

These two SCCs have distinct pollutants: SCC 2701220000 has only NOX emissions, and SCC 2701200000
has emissions for carbon monoxide (CO), volatile organic compounds (VOC) and three VOC hazardous air
pollutants (HAPs): formaldehyde, acetaldehyde, and methanol. Note that there is a fertilizer
adjustment for some of the soils during the growing season in the SCC 2701220000.

Table 8-1: SCCs for biogenic sources

SCC

SCC Level 3

SCC Level 4

2701200000

Vegetation

Total

2701220000

Vegetation/Agriculture

Total

8.2	Sources of data

To be consistent across all geographic areas and with our emissions modeling platform, for the 2020
NEI, we tagged out all SLT-submitted biogenics data to ensure EPA estimates were used everywhere.

8.3	EPA-developed estimates

8.3.1 Continental U.S.

The biogenic emissions for the 2020 National Emissions Inventory (NEI) were computed based on 2020
meteorology data from the Weather Research and Forecasting (WRF) model version 3.8 (WRFv3.8) and
using the Biogenic Emission Inventory System, version 4 (BEIS4) model within the Sparse Matrix
Operator Kernel Emissions (SMOKE) modeling system version 4.9. The BEIS4 model creates gridded,
hourly, model-species emissions from vegetation and soils at 12-kilometer horizontal resolution. The 12-
kilometer gridded hourly data are summed to monthly and annual level (see Figure 8-1) and are mapped
from 12-kilometer grid cells to counties using a standard mapping file.

8-1


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Figure 8-1: Annual VOC emissions for year 2020 for 12km modeling domain

Annual Emissions 2020 12US1 BEIS4 VOC BEIS

Max: 4251.0757

I >1750
1500
I -1250

I -1000 |[
£

750
| -500
<250

BEIS produces biogenic emissions for a modeling domain which includes the contiguous 48 states in the
U.S., parts of Mexico, and Canada. The NEl uses the biogenic emissions from counties from the
contiguous 48 states and Washington, DC. The model-species are those associated with the Carbon
Bond mechanism version 6 (CB6). The NEI pollutants produced are CO, VOC, NOx, methanol,
formaldehyde, and acetaldehyde. VOC is the sum of all biogenic species except CO and nitrogen oxide
(NO). Mapping of BEIS species to NEI pollutants is as follows:

•	NO maps to NOx

•	FORM maps to formaldehyde

•	ALD2 maps to acetaldehyde

•	MEOH maps to methanol

•	VOC is the sum of all biogenic species except CO and NO

BEIS4 has some important updates from earlier versions of BEIS. These include the incorporation of
Version 6 of the Biogenic Emissions Landuse Database (BELD6), the option to include seasonality of
emissions using the 1-meter soil temperature (SOIT2) instead of the BIOSEASON file, and canopy
temperature and radiation environments are now modeled using the driving meteorological model's
(WRFv3.8) representation of LAI rather than the estimated LAI values just from BELD data. See these
CMAQ Release Notes for more technical information on BEIS4.

BEIS4 includes a two-layer canopy model. Layer structure varies with light intensity and solar zenith
angle. Both layers of the canopy model include estimates of sunlit and shaded leaf area based on solar
zenith angle and light intensity, direct and diffuse solar radiation, and leaf temperature [ref 1], The new
algorithm requires additional meteorological variables over previous versions of BEIS. The meteorology
input data fields used by BEIS are shown in Table 8-2.

8-2


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Ta

lie 8-2: Meteorological variables required by BEIS 4

Variable

Description

LAI

leaf-area index

PRSFC

surface pressure

Q2

mixing ratio at 2 m

RC

convective precipitation per meteorological time step

RGRND

solar rad reaching surface

RN

non-convective precipitation per meteorological time step

RSTOMI

inverse of bulk stomatal resistance

SLYTP

soil texture type by USDA category

SOIM1

volumetric soil moisture in top cm

SOIT1

soil temperature in top cm

TEMPG

skin temperature at ground

USTAR

cell averaged friction velocity

RADYNI

inverse of aerodynamic resistance

TEMP2

temperature at 2 m

WSAT_PX

soil saturation from (Pleim-Xiu Land Surface Model) PX-LSM

The Biogenic Emissions Landcover Database version 6 (BELD6) was used as the input gridded land use
information in generating 2020NEI estimates. BELD version 5 (BELD5) was used to generate 2017NEI
estimates. The other input dataset change involved updating the dry leaf biomass (grams/m2) values for
various vegetation types.

The BELD6 includes the following datasets:

•	High resolution tree species and biomass data from Wilson et al. 2013a [ref 2], and Wilson
et al. 2013b [ref 3] for which species names were changed from non-specific common
names to scientific names

•	Tree species biogenic volatile organic carbon (BVOC) emission factors for tree species were
taken from the NCAR Enclosure database (Wiedinmyer, 2001)

o https://www.sciencedirect.com/science/article/pii/S135223100100429Q

•	Agricultural land use from US Department of Agriculture (USDAi crop data layer

•	Global Moderate Resolution Imaging Spectroradiometer (MODIS) 20 category data with
enhanced lakes and Fraction of Photosynthetically Active Radiation (FPAR) for vegetation
coverage from National Center for Atmospheric Research (NCAR)

•	Canadian BELD4 Landuse

Bug fixes included in BEIS4 included the following:

•	Solar radiation attenuation in the shaded portion of the canopy was using the direct beam
photosynthetically active radiation (PAR) when the diffuse beam PAR attenuation coefficient
should have been used.

o This update had little impact on the total emissions but did result in slightly higher
emissions in the morning and evening transition periods for isoprene, methanol and
Methylbutenol (MBO).

•	The fraction of solar radiation in the sunlit and shaded canopy layers, SOLSUN and SOLSHADE
respectively were estimated using a planar surface. These should have been estimated based on
the PAR intercepted by a hemispheric surface rather than a plane.

8-3


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o This update can result in an earlier peak in leaf temperature, approximately up to an
hour.

• The quantum yield for isoprene emissions (ALPHA) was updated to the mean value in Niinemets
et al. 2010a and the integration coefficient (CL) was updated to yield 1 when PAR = 1000
following Niinemets et al 2010b.

o This updated resulted in a slight reduction in isoprene, methanol, and MBO emissions.

The SMOKE-BEIS4 modeling system consists of two programs named: 1) Normbeis4 and 2) Tmpbeis4.
Normbeis4 uses emissions factors and BELD6 landuse and gridded biomass data to compute gridded
normalized emissions for chosen model domain (see Figure 8-2). The BEIS4 emissions factor file
(BEISFAC) contains leaf-area-indices (LAI), dry leaf biomass, winter biomass factor, indicator of specific
leaf weight, Agricultural land type Yes/No (AG_YN), and normalized emission fluxes for 35 different
species/compounds. The BELD6 file is the gridded landuse for 200+ different landuse types. The output
gridded domain is the same as the input domain for the land use data. Output emission fluxes
(BEIS_NORM_EMIS) are normalized to 30°C, and isoprene and methyl-butenol fluxes are also normalized
to a photosynthetic active radiation of 1000 nmol/m2s.

The normalized emissions output from Normbeis4 (BEIS_NORM_EMIS) are input into Tmpbeis4 along
with the MCIP meteorological data, chemical speciation profile to use for desired chemical mechanism,
and soil moisture data file. Figure 8-3 illustrates the data flows for the Tmpbeis4 program. The output
from Tmpbeis includes gridded, speciated, hourly emissions both in moles/second (B4GTS_L) and
tons/hour (B4GTS_S). Biogenic emissions do not use an emissions inventory and do not have SCCs.

Please see the SMOKEv4.9 User's Manual for more information on BEIS4.

Figure 8-2: Normbeis4 data flows for 2020NEI

PROGRAM

FILE

Shows input or

output
			

8-4


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Figure 8-3: Tmpbeis4 data flow diagram for 2020NEI

BEIS NORM EMIS

GSPRO

MET FILE1

SOILINP

PROGRAM

GRID_CRO_2D







B4GTS L

B4GTS S

SOI LOUT

LOG FILE

FILE

Shows input or

output
	>

8.3.2 Alaska, Hawaii, Puerto Rico, and Virgin Islands

The 2020NEI also include biogenic emissions estimates for counties in the states of Alaska and Hawaii,
and for the territories of Puerto Rico and Virgin Islands. The BEIS3.61 modeling system and WRFvB.8
meteorology data for year 2020 were used to produce gridded biogenic emissions for 3 separate
modeling domains at 9-km horizontal resolution. BELD6 data was not available for these modeling
domains so BEIS4 was not used for these states/territories. The modeling domain for Alaska is shown in
Figure 8-4. The land use data used for generating input data for BEIS3.61 included the MODIS 20
category dataset and the FIA version 8.0 used for estimating biomass input information.

Figure 8-4: Alaska 9-km modeling domain

8-5


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The modeling domains for Hawaii, Puerto Rico and Virgin Islands are shown in Figure 8-5 and Figure 8-6,
respectively. Both Puerto Rico and Virgin Islands territories are in the same 9-km modeling domain. The
MODIS 20 category land use dataset was the only dataset used for land use/vegetation input into
BEIS3.61.

Figure 8-5: Hawaii 9-km modeling domain

8-6


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Figure 8-6: Puerto Rico arid Virgin Islands 9-km modeling domain

The 9-kilometer gridded hourly data from these modeling domains are summed to monthly and annual
level and are mapped from 9-kilometer grid cells to counties using a standard mapping file in a similar
manner as was done for the contiguous 48 states. The mapping of BEIS species to NEI pollutants for
these states and territories was also done in the same manner as the contiguous 48 states.

8.4 References for biogenics

1. Bash, J.O., Baker, K.R., Beaver, M.R., Park, J. H., Goldstein, A.H., 2016. Evaluation of improved
land use and canopy representation in BEIS with biogenic VOC measurements in California.
Wilson, Barry Tyler; Lister, Andrew J.; Riemann, Rachel I.; Griffith, Douglas M. 2013a. Live tree
species basal area of the contiguous United States (2000-2009). Newtown Square, PA: USDA
Forest Service, Rocky Mountain Research Station. https://doi.org/10.2737/RDS-2013-0013
Wilson, Barry Tyler; Woodall, Christopher W.; Griffith, Douglas M. 2013b. Forest carbon stocks
of the contiguous United States (2000-2009). Newtown Square, PA: U.S. Department of
Agriculture, Forest Service, Northern Research Station https://doi.org/10.2737/RDS-2Q13-0004

2.

3.

8-7


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United States	Office of Air Quality Planning and Standards	Publication No. EPA-454/R-23-001h

Environmental Protection	Air Quality Assessment Division	March 2023

Agency	Research Triangle Park, NC


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