2 Attachments 

Anita: Thank you for posing the questions (in the January 27, 2012 e-mails below) about biogenic VOC emissions 

in Tables 2 and 5 of the 2005 EPA FR notice that approved the one-hour ozone maintenance plan and redesignated the area to attainment. It took us a while to respond because we had to retrieve the land use and 

biogenic data for the one-hour ozone maintenance plan from the archives. The results of our analysis are 

described below. Please let us know if you have any additional questions or concerns. cda 

 

Response to question on Table 2: The 1990 and 1999 biogenic VOC emissions in Table 2 (Page 13430, FR 

Vol. 70, No. 53) are not comparable because the biogenic emissions were obtained from different plans (i.e., the 

1993 MAG ozone plan versus the 2004 MAG one-hour ozone maintenance plan). These plans used different

biogenic emissions models (PC-BEIS vs. MAGBEIS2), emissions factors, land use categories, and meteorological 

data to derive biogenic emissions. Note that the 1993 plan did not provide a comparative estimate of biogenic 

NOx emissions because the PC-BEIS biogenic model does not calculate biogenic NOx emissions.

Response to question on Table 5: The biogenic emissions in Table 5 (Page 13437, FR Vol. 70, No. 53) were 

derived from the 2004 MAG one-hour ozone maintenance plan, using the MAGBEIS2 model. The increase in 

FW: Biogenic VOCs 

CATHY ARTHUR 

to: 

Anita Lee 

02/08/2012 10:49 AM 

Cc: 

tshin, lbauer, mpoppen 

Hide Details 

From: CATHY ARTHUR <cathyarthur@msn.com> 

To: Anita Lee/R9/USEPA/US@EPA 

Cc: <tshin@azmag.gov>, <lbauer@azmag.gov>, <mpoppen@azmag.gov>

History: This message has been replied to and forwarded. 

2000&2004_MAG_Land_Use & Boundaries.pdf 1-Hr & 8-Hr O3 EF and Land use comparison.xlsx

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biogenic VOC emissions in this table is due to the predominance of urban land uses in the one-hour ozone 

nonattainment area, compared with the much larger modeling domain. A map comparing the land uses in the 

one-hour ozone nonattainment area with the one-hour ozone modeling domain is provided in the attached Figure 

1. Table A (attached) compares the proportion of urban and non-urban land uses for the nonattainment area 

(5,336 sq. km.) and modeling domain (15,824 sq. km.). For both the nonattainment area and modeling domain, 

the 2000, 2006 and 2015 land use data were derived from the MAG 2000 land use/cover and MAG projected 

2010 and 2020 land use/cover data which were available at the time. As shown in Tables B and C, the increase 

in biogenic VOC emissions in the nonattainment area between 2000 and 2015 is due to a 14.4% increase in 

urban land uses, including commercial, residential, park/golf course, and non-emitting (i.e., transportation, airport, 

and parking) areas, at the expense of agricultural and desert/desert park areas. In the modeling domain, the 

increase in urban land uses is only 6.1% and the reduction in agricultural and desert/desert park land more than 

offsets the increase in VOC emissions due to growth in urban land use. Table A shows that the biogenic VOC 

emissions for the one-hour ozone nonattainment area increase between 2000 and 2015, whereas these 

emissions decline for the larger one-hour ozone modeling domain.

In the MAG 2007 eight-hour ozone plan, the 2004 base year biogenic source emissions for the 4-km modeling 

domain were obtained by applying the MAG MEGAN model to MAG 2004 land use/cover data. The MEGAN 

model was developed by ENVIRON based on a 2006 field study in Maricopa County that measured biogenic 

emission factors for local desert plants, agricultural vegetation and trees. The biogenic emissions in the eighthour ozone modeling domain were held constant from the base year of 2004 through the attainment year 2008, 

because there was no projected MAG land use/cover data available for the attainment year of 2008. It is 

important to note that EPA guidance for emissions inventory projections 

(www.epa.gov/ttn/chief/eiip/techreport/volume10/x01.pdf) does not provide any steps or sources of national land 

use data needed to estimate future biogenic emissions. In addition, a recent EPA study of emissions inventories 

also held biogenic emissions constant between the base year of 2005 and the future years 2012 and 2014 (Page 

6, Emissions Inventories, US EPA, June 2010, Docket ID No. EPA-HQ-OAR-2009-0491).

In the 2004 land use/cover data, urban land use (commercial, residential, parks/golf course, and transportation) 

represents 26.9% of the eight-hour ozone nonattainment area (Table D) versus 39.1% of the one-hour ozone 

nonattainment area in 2006 (Table A). This difference is due to the fact that the eight-hour ozone nonattainment 

area is1.34 times larger than the one-hour ozone nonattainment area and therefore, includes a much larger 

proportion of non-urban land uses. A map of the land uses in the eight-hour ozone nonattainment area and 

eight-hour ozone modeling domain is provided in Figure 2. In addition, the MEGAN biogenic emissions factors 

differ significantly from MAGBEIS2. The MEGAN VOC emission factor for residential areas is 441.8 ug/m2/hr 

versus 668.5 ug/m2/hr for MAGBEIS2, while the MEGAN VOC emission factor is 2,221 ug/m2/hr for agriculture 

compared with the MAGBEIS2 factor of 125.3 ug/m2/hr (Tables E and F). Due to the increased size of the eighthour ozone nonattainment area and the major changes in emission factors attributable to different models, the 

biogenic VOC emission increase due to urban growth is more than offset by the reduction in biogenic VOC

emissions caused by decreases in agricultural and desert/desert park land areas.

 

In conclusion, holding biogenic emissions constant between the base year of 2004 and the attainment year of 

2008 in the 2007 eight-hour ozone plan is considered to be a reasonable and conservative assumption. 

From: Anita Lee [mailto:Lee.Anita@epamail.epa.gov] 

Sent: Friday, January 27, 2012 2:56 PM 

To: Cathy Arthur; Lindy Bauer; Matthew Poppen; Taejoo Shin 

Subject: Biogenic VOCs 

 

Hello again, 

Apologies for the multiple emails. 

See also Table 5 of the same FR notice. It shows that over 1999, 2006, and 2015, that biogenic 

VOC emissions go up and biogenic NOx emissions go down. There is also a corresponding 

discussion that includes statements of increasing residential land use at the expense of agricultural 

land use, and that residential land use is expected to have a higher biogenic VOC emission factor 

than agricultural land. I realize the FR notice was written by EPA, so if this information does not 

correctly characterize the modeling from MAG, please also feel free to let me know that. 

Thanks again! 

anita 

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Anita Lee, PhD 

Environmental Scientist 

US EPA, Region 9 

Air Planning Office 

75 Hawthorne Street (AIR-2) 

San Francisco, CA 94105 

ph: (415) 972-3958 

fax: (415) 947-3579 

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------------------ 

Hello all, 

Thanks so much for your call today. 

I found the table that made me think biogenic VOC emissions would increase with the urbanized 

land use - It's from 70 FR 13425 (March 21, 2005). Table 2 on page 13430 shows estimated values 

for biogenic VOC increased from 1990 to 1999. I think I understood from our conversation today 

that this change was due to a change in biogenic estimation models used, and if/when the same 

model is used consistently, the model shows a decrease in VOC emissions. Is that right? Please feel 

free to point me to your past submittals to help me understand this further. Thanks so much! Have 

a great weekend, 

anita 

* * * * * * * * * * * * * * * * * * * * 

Anita Lee, PhD 

Environmental Scientist 

US EPA, Region 9 

Air Planning Office 

75 Hawthorne Street (AIR-2) 

San Francisco, CA 94105 

ph: (415) 972-3958 

fax: (415) 947-3579 

* * * * * * * * * * * * * * * * * * * * 

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