EMISSIONS INVENTORY BASE YEAR FOR CRITTENDEN COUNTY NOx and VOC 

REPORTING REQUIREMENTS FOR THE NONATTAINMENT AREA UNDER THE 2008 

EIGHT-HOUR OZONE NAAQS 

This document provides a technical review of a revision to the Arkansas State Implementation 

Plan (SIP) to meet Clean Air Act (CAA) Emission Inventory (EI) reporting requirements for the 

Crittenden County nonattainment area under the 2008 eight-hour ozone standards submitted by the 

Arkansas Commission on Environmental Quality (ADEQ) on July16, 2014. 

A. General Requirements 

Under the CAA sections 172(c)(3) and 182 (a)(1), states are required to submit emissions 

inventory (EI) information for all relevant sources for areas that are designated nonattainment for any of 

the National Ambient Air Quality Standards (NAAQS) for each area designated nonattainment for a 

NAAQS. On March 27, 2008, the United States Environmental Protection Agency (EPA) lowered the 

primary and secondary eight-hour ozone NAAQS to 0.075 parts per million (ppm) (73 FR 16436).

1

 On 

May 21, 2012, the EPA published in the Federal Register (77 FR 30088) final designations for the 2008 

ozone standard. The Crittenden County area was designated and classified as marginal nonattainment. 

The effective date of the final rule is July 20, 2012. 

The EPA’s published the final 2008 ozone standard SIP requirements rule on March 6, 2015, 

which specified that states use 2011 as a base year to address EI requirements. The nonattainment area 

base year EI emission is due no later than 24 months from the July 20, 2012 effective date and then every 

three years thereafter. An emissions inventory is an estimation of actual emissions of air pollutants in an 

area. Volatile organic compounds (VOCs) and oxides of nitrogen (NOx) are known as “ozone 

precursors”, as they react with oxygen and sunlight to form ozone. Motor vehicle exhaust and industrial 

emissions, gasoline vapors and chemical solvents emit NOx and VOCs. Controlling sources of NOx and 

VOC emissions can lower ozone levels in the ambient air. Thus, the emissions inventory for an ozone 

nonattainment area contains VOC and NOx emissions. The EIs provide data for a variety of air quality 

planning tasks including establishing baseline emission levels calculating federally required emission 

reduction targets, emission inputs into air quality simulation models, and tracking emissions over time. 

The total EI of VOC and NOX for an area are summarized from the estimates developed for four general 

categories of emissions sources: point, area, mobile, and biogenic. 

B. Background 

The majority of NOX emissions in Crittenden County come from Area sources. Area sources are smallscale industrial, commercial, and residential sources that use materials or perform processes that generate 

emissions. These sources could include printing processes, industrial coating and degreasing operations, 

gas services, or structure fires. The sub-set of mobile sources known as on-road mobile sources (vehicles 

such as cars and trucks that normally travel on public roadways).

                                                            

1

 We refer to this NAAQS as the 2008 ozone NAAQS or standard. 
2008 Eight-Hour Ozone Standard (2008 to Present) 

On May 21, 2012, Crittenden County was designated as a marginal nonattainment area with a design 

value of 0.082 ppm (77 FR 30088), based on ozone monitoring data from the period of 2006 to 2008. 

1997 Eight-Hour Ozone Standard (1997 to Present) 

In July 1997, the EPA announced a revised NAAQS for ground-level ozone. The EPA phased out and 

replaced the previous one-hour standard with an eight-hour standard set at 0.08 ppm to protect the public 

health against longer exposure to this air pollutant. The eight-hour ozone standard became effective on 

September 16, 1997. 

Effective April 14, 2004, the Memphis Ozone Nonattainment Area (MONA), which includes Crittenden 

County was designated nonattainment for the 1997 eight-hour ozone standard and classified as marginal. 

C. EPA’s Analysis 

The EPA reviewed the Arkansas submittal for consistency with the EPA regulations. The following is a 

summary of the analysis based on the information provided by Arkansas. 

The 2011 Base Year Inventory is the starting point for calculating the reductions necessary to meet the 

requirements of the CAA. Sections 172 (c)(3) and 182(b)(1) of the CAA require that nonattainment plan 

provisions include an inventory of actual emissions from all sources of relevant pollutants in the 

nonattainment area. The federal Air Emissions Reporting Requirements (AERR) rule requires states to 

develop and submit periodic EIs to the EPA every three years. The 2011 inventory was the first periodic 

emission inventory (PEI) submitted under AERR. Per the AERR, the 2011 PEI was reported to the EPA’s 

National Emissions Inventory (NEI) as a comprehensive and detailed estimate of air emissions, including 

ozone precursors (NOx and VOC). The year 2011 is also the year for a required EI submission under the 

existing AERR rule. As directed by the AERR, the NEI includes statewide coverage. Annual and summer 

day emissions are reported on a three-year cycle for the AERR. States can rely on periodic AERR EI 

submittals to satisfy ongoing SIP EI submission requirements every three years. The Arkansas DEQ 

submitted the 2011 base year inventory to the EPA as part of a SIP revision for the Crittenden County 8-

hour ozone non-attainment area. The EPA reviewed the 2011 base year inventory and determined that it 

was developed in accordance with EPA guidelines. The inventory includes all area, point, non-road 

mobile, and on-road mobile source emissions in the Crittenden County ozone nonattainment area. The 

inventory also includes a description of the methods used to estimate emissions: 

Point Source Emissions: Industrial sources are required to submit emissions data to the ADEQ annually 

and certify that the data reported is accurate to the best of their knowledge. The ADEQ stores the data in 

the State and Local Emissions Inventory System (SLEIS). For the 2011 EI, facilities could use SLEIS to 

electronically submit their EI reports to the ADEQ for review. All submitted data is reviewed by the 

ADEQ for quality assurance purposes and then stored in the SLEIS database. At the end of the annual 

reporting cycle, point source emission data is reported each year to the EPA for inclusion in the National 

Emission Inventory (NEI). 

Area Source Emissions: Area sources are small-scale industrial, commercial, and residential sources that 

generate emissions. The ADEQ developed the 2011 area source emission inventory in accordance with 

the AERR reporting requirements, using methodologies and data from EPA- prescribed methods in 
“Procedures for the Preparation of Emission Inventories for Carbon Monoxide and Precursors of Ozone 

Volume 1: Guidance for Stationary Sources” found at:

http://www3.epa.gov/ttn/naaqs/aqmguide/collection/cp2/bakup/19910501_oaqps_epa-450_4-91-

016_ei_preparation_stationary_sources.pdf. The EPA developed EIs for states to us 

e for many source categories as part of the NEI. These source categories include but are not limited to 

industrial coatings, degreasing; residential, commercial/institutional, and industrial fuel use, commercial 

cooking; aviation fuel use; and consumer products. We have reviewed these approaches and have 

determined that they are acceptable. 

Non-road Emissions Inventory: The non-road category is composed of a diverse collection of equipment, 

many of which are powered by diesel engines. Non-road emissions sources include, but are not limited to: 

agricultural equipment, locomotives, drilling equipment, lawn and garden equipment, and drilling rigs. 

Arkansas utilized the National Mobile Inventory Model (NMIM) for this data. NMIM runs a series of 

models to calculate pertinent emissions, including the NONROAD Model for non-road engines, 

equipment and vehicles. NONROAD has a primary function used for estimating air pollutant inventories 

by professional mobile source modelers, such as state air quality officials and consultants. We find the 

approach and methodology used by the ADEQ acceptable. 

On-road Emission Inventory: On-road emission sources consist of automobiles, trucks, motorcycles, and 

other motor vehicles travelling on public roadways. On-road mobile source emissions are usually 

categorized as either combustion-related emissions or evaporative hydrocarbon emissions. Combustionrelated emissions are estimated for vehicle engine exhaust. Evaporative hydrocarbon emissions are 

estimated for the fuel tank and other evaporative leak sources on the vehicle engine exhaust. The ADEQ 

updated the on-road emissions using EPA’s Motor Vehicle Emissions Simulator (MOVES2010b) for onroad mobile sources. In April, 2012, the EPA released MOVES2010b with several improvements to the 

general model performance. To calculate pollution from on-road mobile sources, emission rates are 

estimated as a function of county, vehicle type, roadway type, hour, and operating speed. These rates are 

then matches with appropriate activity from transportation data parameters including- but not limited tovehicle miles travelled, number of vehicles parked, and hours spent in idle mode. The EPA reviewed the 

on-road emission estimates approach and methodology and determined that they are acceptable. 

The 2011 base year emissions data for Crittenden County are provided in Table 1 below. 

   
Table 1- Base Year Emissions Inventory, 2011 Data 

Category Ozone Season 

Daily NOx 

Annual NOx Ozone Season 

Daily VOC 

Annual VOC 

Units Tons/day Tons/year Tons/day Tons/year 

Point 0.0017 .063 .051 186.84 

Area 8.70 3,165.17 24.90 8,868.94 

Non-road Mobile 2.11 582.63 3.66 881.35 

On-road Mobile 6.80 2,542 2.42 845 

Total 17.61 6,290.43 31.49 10,782.13 

Biogenic Sources: Biogenic sources include VOC emissions from crops, lawn grass, and trees as well as a 

small amount of NOx emissions from soils. Plants are sources of VOC emissions such as isoprene, 

monoterpene, and alpha-pinene. Biogenic emissions are estimated by the EPA using its biogenic 

emissions inventory tool. 

D. Summary and Recommendations: 

Pursuant to 40 Code of Federal Regulations Part 51.102 and after proper notice, the ADEQ 

conducted a public hearing to consider the EI revision to the SIP. Proper notice included prominent 

advertisement in the areas affected at least 30 days prior to the date of the hearing. The public hearing was 

held in West Memphis on March 18, 2015. Data, views, and recommendations of interested persons 

regarding the proposed SIP revision were submitted to the ADEQ during the comment period and were 

considered for the SIP revision. The ADEQ has used acceptable techniques and methodologies to develop 

the 2011-base year emission inventories for the 2008 ozone NAAQS for Crittenden County to satisfy 

sections 172 and 182 of the CAA. 

Therefore we recommend approval of the Arkansas State Implementation Plan (SIP) revisions to 

meet the CAA EI reporting requirements for the Crittenden County nonattainment area under the 2008 

ozone NAAQS, submitted by the ADEQ on August 28, 2015 .