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Comparing the Emission Inventories for the San Joaquin Valley

State Implementation Plans

Emission inventories are one of the fundamental building blocks in the development of 

a State Implementation Plan (SIP or Plan). Emission inventories provide the basis from 

which the State builds an attainment demonstration; therefore, substantial time and 

resources are expended to ensure the inventory reflects the best information available 

at the time the SIP is submitted to the U.S. Environmental Protection Agency (U.S. 

EPA). 

Developing and maintaining an accurate and comprehensive emission inventory is an 

iterative process. ARB and local air districts’ staffs continually review the 

methodologies and technical data behind the emission estimates and perform updates 

as necessary to reflect better understanding of the emission sources. Therefore,

emission inventories submitted with subsequent SIPs are likely to present different 

estimates for some categories.

In California, responsibility for emission inventory development is split between ARB 

and 35 air districts. The San Joaquin Valley Air Pollution Control District (District) has

responsibility for all point sources within their jurisdiction, some area sources, and 

aircraft emissions. ARB has responsibility for the balance of the area sources, all onroad sources, and the balance of off-road sources.

District staff work with facility operators to develop point source inventories, which are 

reported annually to ARB. In most cases, these annual updates reflect actual emission 

estimates based on facility activity rates, changes in industrial processes, and changes 

in the number of operating facilities due to startups or closures. The District and ARB 

update area source emission estimates periodically, primarily as needed for SIP

revisions. Methodology updates may include changes in estimation methods, updated 

emission factors, and/or updated activity data. On-road and off-road models are also 

updated regularly, both as part of SIP development and in support of ARB’s own 

regulations.

U.S. EPA regulations require that SIPs include a base year inventory and forecasted 

inventories for milestone years. Forecasted inventories are a projection of the base 

year inventory that reflects expected growth trends in each sector and emission 

reductions due to adopted control measures. As with the base year inventory, 

forecasted inventories represent our best assessment of growth trends at the time. 

Subsequent inventory forecasts are likely to reflect differences due to changes in the 

growth trends, estimation methodology refinements and improvements, additional 

control measures, and sometimes corrections to the original base-year emissions.

The following is a discussion of the various emission inventories under review by U.S. 

EPA:
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Current Emissions Inventory

The most current emission inventory was submitted to U.S. EPA as part of the San 

Joaquin Valley 2015 Plan for the 1997 PM2.5 Standard. This inventory uses 2012 as 

the base year. The point source emissions reflect actual data reported by the facilities 

through 2012, and in most instances the forecasted emissions (2013 and subsequent 

years) reflect growth assumptions that were reviewed and updated as recently as 2012. 

Areawide emission estimates reflect updates to several methodologies, and mobile 

source emissions were generated with updated versions of ARB’s on-road model 

(EMFAC2014) and various modular updates of the off-road model. The inventory 

reflects control measures adopted as of May 2014. 

2007 PM10 Maintenance Plan Inventory

The 2007 PM10 Maintenance Plan inventory used 2002 as the base year. The point 

and areawide emission forecasts are based on projections of the 2002 inventory that 

reflect growth forecasts developed in 2001. Areawide emission estimates are based on 

methodologies developed in the late 1990s to early 2000s. Mobile source emission

estimates for all the years were generated by EMFAC2007 and OFFROAD2007 

models. The inventory reflects control measures adopted as of June 2006.

The most significant differences between the 2007 PM10 Plan and the current inventory 

are as follows:

• ARB and District Rule updates – The current inventory accounts for several 

District rules that were not included in the 2007 PM10 Plan. These include 

District rules for open burning; boilers, steam generators and process heaters; 

dryers, dehydrators and ovens; internal combustion engines; confined animal 

operations; wine fermentation and storage; automotive coatings, and oil 

production wells. In addition, the current inventory also reflects ARB rules 

impacting mobile source emissions (heavy-duty truck reflash; idling regulation; 

on-road and off-road Carl Moyer incentives; transportation refrigeration units, 

portable diesel engines, large spark ignition engine regulation, and ocean going 

vessels) and consumer products.

• Baseline corrections – The current inventory reflects baseline corrections to the 

Manufacturing and Industrial and Food and Agriculture categories that result in a 

reduction of 30 tons per day of NOx emissions.

• Managed burning and disposal -- The emission estimates for agricultural and 

prescribed burning in the 2007 Plan are based on projections made from the 

acreage burned in 2002 or earlier. The current inventory reflects emissions 

based on the 2012 agricultural crop acreage burned resulting in a reduction of 

9.4 tons of NOx compared to previous projections. The new estimates also

reflect the reclassification of “Wildfire Use” as a natural source category, further 
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reducing the emissions of NOx by 0.8 tons. The managed burning emissions for 

2005 in the 2016 SIP inventory for PM10 are reduced from the PM10 plan 

inventory reflecting actual estimates based on the agricultural crop and forest 

land acreage burned under the District’s Agricultural Burning Program. 

• Off-Road models update – The current inventory reflects updates to ARB’s offroad source emissions using a newer suite of category-specific models

developed to support recent ARB regulations. These updates include 

locomotives, ocean-going vessels, recreational boats, transportation refrigeration 

units, construction equipment, oil drilling and workover equipment, cargo 

handling equipment, and farm equipment.

2011 Ozone SIP Revision Inventory

The original 2007 Ozone SIP Plan was built on the same underlying elements (base 

year, growth assumptions, area source methodologies, mobile source model versions, 

and control measures) as the 2007 PM10 Maintenance Plan inventory discussed above. 

The 2011 Ozone SIP Revision inventory is an update that incorporates corrections to 

the baseline, emission reductions from ARB and District rules that were not initially 

included, and adjustments to the on-road and off-road emissions due to impacts from 

the economic recession that started in 2007.

The most significant differences between the 2011 Ozone SIP Revision and the current 

inventory are due to large decreases in the actual reported emissions for several point 

source categories (cogeneration, oil and gas production, food and agriculture, glass 

manufacturing and composting), compared to their projected emissions in the earlier 

plan. Other significant differences include:

• Managed burning and disposal -- The emission estimates for agricultural and 

prescribed burning in the 2007 Plan are based projections made from the 

acreage burned in 2002 or earlier. The current inventory reflects emissions 

based on the 2012 agricultural crop burned acreage, which has undergone 

significant reductions since the earlier plan. The new estimates also reflect the 

reclassification of “Wildfire Use” as a natural source category.

• Off-Road models update – The current inventory reflects updates to ARB’s offroad source emissions using a newer suite of category-specific models

developed to support recent ARB regulations. These updates include 

locomotives, ocean-going vessels, recreational boats, transportation refrigeration 

units, construction equipment, oil drilling and workover equipment, cargo 

handling equipment, and farm equipment.

• Farming Operations – The livestock emission estimates for VOC only in the 2011 

Ozone SIP Revision inventory was based on California Department of Food and 

Agriculture livestock population estimates from 2000. The current inventory 
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reflects population estimates from the U.S. Department of Agriculture (USDA) 

2012 Census of Agriculture and updated emission factors provided by the 

District. Additionally, the current inventory includes VOC emission estimates for 

silage, a category that was not inventoried in the 2011 Ozone SIP Revision.

2012 PM2.5 Plan Inventory

The 2012 PM2.5 SIP inventory represents the next major inventory update since the 

2011 Ozone SIP Revision. In addition to the 2011 Ozone SIP Revision updates, it 

incorporates several other updates that are also reflected in the current inventory. It 

uses 2007 as the base year, so the point source inventory reflects actual emissions 

reported by the facilities through that year. The inventory also incorporates a major 

revision of the growth profiles (conducted in 2011-2012) to reflect more recent 

socioeconomic trends, including the impact of the 2007 recession. Several area source 

methodologies were updated to reflect recent activity data and /or revised emission 

factors. The on-road emission source estimates were generated using EMFAC2011 

with activity data provided by the local transportation planning agencies, and the offroad mobile source estimates reflect updates to several categories. The inventory 

reflects control measures adopted as of June 2011.

Since the 2012 PM2.5 Plan inventory reflects many of the updates included in the 

current inventory, the differences between them are much smaller. All of the differences 

in point source emissions can be attributed to year-to-year fluctuations in source 

activity. The most significant differences include:

• Managed burning and disposal -- The agricultural burning emissions in the 2012 

Plan inventory were forecasted from the 2007 agricultural crop acreage burned 

under the District’s Agricultural Burning Program acreage; however, in the 

current inventory they were estimated from the 2012 actual acreage.

• Off-Road Models update. For the locomotive and recreational boat emissions 

categories the 2012 Plan inventory included preliminary adjustments for these 

two categories based on on-going model development. The current inventory 

includes estimates from the final model updates.

• Farming operations – The livestock emissions in the 2012 Plan inventory were 

forecasted from an estimate based on cattle population estimates from the 2007 

USDA Census of Agriculture. The current inventory reflects emissions based on 

livestock population estimates from the 2012 USDA Census. For PM2.5, the 

current inventory shows 2.11 tons decrease in 2017, mainly in two categories: 

Tilling Dust and Feedlot Cattle. For Agricultural Land Preparation and Harvest 

Operations, ARB updated the emission estimation methodology and the particlesize profile of particulate matter. For Livestock Husbandry, ARB updated the 

emission estimation methodology with new cattle population and emission 

factors.