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STATE OF CALIFORNIA

CALIFORNIA AIR RESOURCES BOARD

STAFF REPORT

ANALYSIS OF THE 

2012 PM2.5 EMISSIONS INVENTORY SUBMITTAL 

TO THE STATE IMPLEMENTATION PLAN FOR 

THE SAN FRANCISCO BAY AREA 

I. BACKGROUND

The federal Clean Air Act (Act) establishes planning requirements for those areas that 

exceed the health-based National Ambient Air Quality Standards (standards). Areas 

are designated as nonattainment based on monitored exceedances of these standards. 

These nonattainment areas must develop and implement a State Implementation Plan 

(SIP) that demonstrates how they will attain the standards by specified dates. 

In December 2006, the United States Environmental Protection Agency (U.S. EPA) 

lowered the 24-hour standard for fine particulate matter (PM2.5) from 65 g/m3to 

35 g/m3. Effective December 14, 2009, U.S. EPA designated the San Francisco Bay 

Area in the Bay Area Air Quality Management District (District) as nonattainment for this

more stringent 24-hour PM2.5 standard. The subsequent SIP submittal deadline is 

December 14, 2012. 

II. CLEAN DATA POLICY REQUIREMENTS

Under the U.S. EPA’s Clean Data Policy for the Fine Particulate National Ambient Air 

Quality Standards (Clean Data Policy), areas designated nonattainment that 

subsequently attain the standard prior to the SIP submittal deadline are eligible for 

reduced regulatory requirements. Based on quality-assured federal reference method 

monitoring data for 2009-2011, the San Francisco Bay Area has demonstrated 

attainment of the 24-hour PM2.5 standard (Table 1). 

Table 1

98th Percentile

(g/m3)

3-year Average

(g/m3)

2008 2009 2010 2011 2008-2010 Design Value 2009-2011 Design Value

36 34.1 29.2 30.6 31 30
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On December 8, 2011, The Air Resources Board (ARB) submitted a request to

U.S. EPA to find the San Francisco Bay Area in attainment of the 35 g/m324-hour 

PM2.5 standard. This clean data finding under the Clean Data Policy suspends the 

majority of the planning elements under the Act, including the attainment demonstration, 

reasonably available control measures, and contingency elements of a SIP. The only 

planning element required under the Clean Data Policy is an emission inventory. Other 

requirements under the Act, specifically transportation conformity and new source 

review, are still applicable and are discussed in Section IV of this document.

III. EVALUATION OF THE SAN FRANCISCO BAY AREA EMISSION INVENTORY

The District developed the 2010 Bay Area Winter Emissions Inventory for Primary 

PM2.5 and PM Precursors (Emission Inventory SIP Submittal) to address the emission 

inventory requirements under the Clean Data Policy. The District Board of Directors 

adopted the Emission Inventory SIP Submittal at a public hearing on November 7, 2012. 

An essential tool to support the evaluation, control, and mitigation of air pollutants, an 

emission inventory is a systematic listing of air pollutant sources, along with an 

accounting of the amount of pollutants emitted by each source or category over a given 

period of time. This accounting is an estimate of emissions, not direct ambient 

concentration measurements. U.S. EPA requires states to submit an attainment year 

inventory that includes directly emitted PM2.5 emissions, as well as emissions of 

precursors that contribute to the formation of particles formed through chemical 

reactions in the atmosphere, in particular, oxides of nitrogen (NOx), oxides of sulfur 

(SOx), reactive organic gases (ROG), and ammonia (NH3).

In addition, U.S. EPA allows the use of a seasonal inventory, rather than an annual 

inventory, when it has been demonstrated that the seasonal emissions have 

significantly led to the original nonattainment status. Analysis of daily air quality data

has demonstrated that high PM2.5 concentrations occur primarily during the winter 

season. Exceedances during other seasons have been demonstrated to have been 

influenced by exceptional events, such as wildfires, but are outside of regulatory control. 

The District’s Emission Inventory SIP Submittal is the most up-to-date emission 

inventory for the San Francisco Bay Area. Based on the daily winter season PM2.5

emissions for 2010, it is typical of the 2008-2010 attainment demonstration years. The 

winter-time 2010 baseline inventory includes PM2.5, NOx, SOx, ROG, and NH3

emissions. Residential wood burning and gasoline and diesel vehicles comprise about 

two thirds of the directly emitted PM2.5 emissions. On-road motor vehicles make up the 

largest source of NOx and ROG emissions. 
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IV. OTHER CLEAN AIR ACT REQUIREMENTS

a. Conformity

The Act requires that procedures be in place to ensure that there is conformity of federal 

actions and federally funded transportation projects efforts to attain federal air quality 

standards. Under the Clean Data Policy, the District had a choice to either set 

transportation conformity budgets or allow the existing transportation conformity process 

to continue. The District chose to allow the existing process to continue. Under this 

process, the District works closely with the Metropolitan Transportation Commission to 

ensure that emissions from new transportation projects are less than the baseline (or 

attainment year) emissions.

b. New Source Review

U.S. EPA’s New Source Review (NSR) requirements specify that there must be a 

method to identify and quantify allowable emissions of pollutants from construction and 

operation of major new or modified stationary sources in the District. Permits for new or 

modified stationary sources are required. This requirement is met with a revised District 

rule (Regulation 2) implementing NSR requirements.

V. STAFF RECOMMENDATION

ARB staff has reviewed the 2010 Bay Area Winter Emissions Inventory for Primary 

PM2.5 and PM Precursors and consulted with District staff during this review. ARB staff 

finds that the Emission Inventory SIP Submittal meets all applicable Act and Clean Data 

Policy requirements. Therefore, staff recommends that the Board adopt the Emission 

Inventory SIP Submittal as a revision to the California SIP for submittal to U.S. EPA.