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STATE OF CALIFORNIA

CALIFORNIA AIR RESOURCES BOARD

STAFF REPORT

ANALYSIS OF THE 

2012 PM2.5 EMISSION INVENTORY SUBMITTAL 

TO THE STATE IMPLEMENTATION PLAN FOR 

THE CHICO PLANNING AREA

I. BACKGROUND

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

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

designated as nonattainment based on monitored exceedances of the NAAQS. These 

nonattainment areas must develop and implement a State Implementation Plan (SIP) 

that demonstrates how they will attain the NAAQS by specified dates. 

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

lowered the 24-hour NAAQS for fine particulate matter (PM2.5) from 65 μg/m3 to 

35 μg/m3

. Effective December 14, 2009, U.S. EPA designated the Chico, CA/Butte 

County (partial) Planning Area (Chico Planning Area) in the Butte County Air Quality 

Management District (Butte District) as nonattainment for this more stringent 24-hour 

PM2.5 NAAQS. 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 NAAQS prior to the SIP submittal deadline are eligible for 

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

monitoring data for 2008-2010, the Chico Planning Area has demonstrated attainment 

of the 24-hour PM2.5 NAAQS (Table 1). The Chico Planning Area also continues to 

attain based on the most recent air quality data for 2009-2011. 

Table 1

98th Percentile

(μg/m3)

3-year Average

(μg/m3)

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

35.7 30.0 29.0 46.2 32 35
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On June 2, 2011, ARB submitted a request to U.S. EPA to find the Chico Planning Area

in attainment of the 35 μg/m3 24-hour PM2.5 NAAQS. This clean data finding under the 

Clean Data Policy, suspends the majority of the planning elements under the Clean Air 

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 Clean Air 

Act, specifically transportation conformity and new source review, are still applicable 

and are discussed in Section IV of this document.

III. EVALUATION OF THE BUTTE COUNTY AQMD EMISSION INVENTORY

The Butte District developed the 2012 PM2.5 Emission Inventory Submittal to the State 

Implementation Plan for the Chico, CA/Butte County (partial) Planning Area (Emission 

Inventory SIP Submittal) to address the emission inventory requirements under the 

Clean Data Policy. The Governing Board of the Butte District adopted the Emission 

Inventory SIP Submittal at a public hearing on September 27, 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, 

as well as source apportionment analysis detailed in the Emission Inventory SIP 

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

inventory for the Chico Planning Area. Based on the daily winter season PM2.5

emissions for 2011, it is typical of both the 2008-2010 and 2009-2011 attainment 

demonstration years. The winter-time 2011 baseline inventory includes PM2.5, NOx, 

SOx, ROG, and NH3 emissions. Residential wood heating comprises almost half of 
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winter directly emitted PM2.5 emissions, while mobile sources are the largest 

contributors to NOx and ROG emissions. 

IV. OTHER CLEAN AIR ACT REQUIREMENTS

a. Conformity

The Clean Air Act requires that procedures be in place to ensure that there is conformity 

of federal actions and federally funded transportation projects efforts to attain the 

NAAQS. The Butte District has two rules in place to ensure both general conformity 

(Rule 1103) and federal transportation conformity (Rule 1102). Under the Clean Data 

Policy, the Butte District had a choice to either set transportation conformity budgets or 

allow the existing transportation conformity process to continue. The Butte District 

chose to allow the existing process to continue. Under this process, the Butte District 

works closely with the Butte County Association of Governments 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 Butte District. Permits for 

new or modified stationary sources are required. This requirement is met with a new 

Butte District rule (Rule 432) implementing NSR requirements; it will be submitted 

separately to ARB and U.S. EPA as a revision to the California SIP.

V. STAFF RECOMMENDATION

ARB staff has reviewed the Emission Inventory SIP Submittal to the State 

Implementation Plan for the Chico, CA/Butte County (partial) Planning Area and 

consulted with Butte District staff during this review. ARB staff finds that the Emission 

Inventory SIP Submittal meets all applicable Clean Air 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.