4	Monitoring, Emissions and Modeling Tools

4.1	MONITORING NETWORKS AND SAMPLING/MEASUREMENT METHODS

This section describes the national air quality monitoring programs that provide the foundation for characterizing air quality, and associated sampling and analystechniques. The various special studies and intensive field programs complement the national monitoring efforts, and in many instances historically have provided the majority of data for ozone precursors, elevated (i.e., vertical profiles) concentrations and fine particles. These studies (e.g., SOS, SCAQS) are discussed in Section 3.

4.1.1	Ozone and precursors

4.1.1.1	Ozone

Overview of Existing Networks and 40 C.F.R. 58 Requirements.	The 40 C.F.R. 58 Ambient Air Quality Surveillance regulation contains criteria and requirements for the establishment and operation of ozone ambient air monitoring and data reporting. Specific topics discussed within 40 C.F.R. 58 include the following:

Quality assurance procedures for ozone analyzer operation and data handling.

Methodology employed at ozone monitoring stations.

Ozone monitoring schedules, or seasons.

Ozone monitor siting parameters

Ozone monitoring network requirements and recommendations for the National Ambient Monitoring Stations (NAMS), the State/local Ambient Monitoring Stations (SLAMS), and the Photochemical Assessment Monitoring Stations (PAMS) networks.

Ozone data reporting requirements.

Ambient air monitoring data collected according to the 40 C.F.R. 58 regulation are inputted by the State/local air quality management agencies into the U.S. EPA's central data repository, the Aerometric Information Retrieval System (AIRS), and then used for a variety of purposes. Principal uses of these data are to determine air quality status, to make attainment decisions with respect to the ozone National Ambient Air Quality Standards (NAAQS), to assist in developing necessary control strategies to ensure attainment of the ozone NAAQS, to assess national trends in ozone air pollution, to inform the public of their air quality, and to determine the population's exposure to the ozone concentrations in ambient air. The U.S. EPA's goal of attaining the ozone NAAQS in all areas of the United States is directly dependent upon the availability of ambient air quality data. Additionally, the U.S. EPA, State and local air quality management agencies, environmental groups, industrial groups, and academic organizations use these data to study atmospheric chemistry, e.g., the formation of ozone, and to determine the most appropriate and effective control strategies necessary to reduce air pollution.

The authority for the 40 C.F.R. 58 Ambient Air Quality Surveillance regulation is provided within 42 U.S.C.A. §§ 7403, 7410, 7511(a), 7619.

The State and Local Air Monitoring Stations (SLAMS) networks are the primary source for ozone ambient air quality data used by the U.S. EPA and the State and local air quality management agencies. Of the 981 total ozone monitoring sites reported to the U.S. EPA's AIRS (Figure 4.1.1) database, 780 of these, or approximately 80%, are SLAMS ozone sites. The wide variety of monitoring objectives associated with the SLAMS ozone monitoring networks can include, but are certainly not limited to, determining population exposure, assessing ozone transport into an area, determining the maximum ozone concentrations in an urban area, and determining background ozone concentrations. Most of the SLAMS are located near or within urban areas; however some (roughly 10%) are located in more rural settings, particularly those with transport assessment or background concentration determination objectives. The 40 C.F.R. 58 regulation does not specify the exact number of SLAMS that must be installed and operated by each State/local agency. This number and the location of SLAMS sites are generally determined by the affected State/local air quality management agency based on the specific characteristics of the area to be monitored and the monitoring objectives, and approved by the appropriate U.S.EPA Regional Office.

The National Air Monitoring Stations (NAMS) are subsets of the SLAMS. The NAMS were established to provide consistent air quality data that could be used to assess national ozone trends and to make national ozone policy decisions. Of the total number of SLAMS ozone monitoring sites, there are approximately 229 ozone NAMS sites in operation at this time. The 40 C.F.R. 58 regulation requires that two NAMS sites be established within any urban area with a population of 200,000 or more. One of these sites is located to assess population exposure and the second is located to determine the maximum concentrations for that urban area. The U.S. EPA Administrator's designee provides the approval authority for all NAMS sites.

Other ozone sites.	In addition to the SLAMS ozone monitoring networks (which includes both NAMS and PAMS networks), the State and local air quality management agencies will frequently collect ozone concentration data by using Special Purpose Monitoring networks (SPMs). SPMs are useful to State/local agencies who are interested in operating sites for a short time, or for some specific study of ozone photochemistry. SPMs do not have the same regulatory requirements associated with their data reporting, siting, and operation as SLAMS, although the data from some SPMs have been used in regulatory decisions previously. There are approximately 172 SPMs listed in the U.S. EPA's AIRS database at present, which represents approximately 17% of the total ozone monitoring stations currently in operation.

Reporting data into the U.S.EPA's AIRS database is not restricted to only the U.S. EPA and State and local air quality management agencies. Other federal agencies, in particular the National Park Service, have operated ozone monitoring stations and report the data into the U.S.EPA's AIRS database. Approximately 29 ozone monitoring sites (or 3% of the total number of ozone sites) operated by the non-EPA federal agencies are currently in AIRS. These 29 sites are generally located in or near federal lands, such as national parks, national monuments, national lake shores, and similar rural locations.

4.1.1.2	Ozone precursors

[Discuss early AM precursor program as lead in to PAMS]

PAMS. The Photochemical Assessment Monitoring Stations (PAMS) networks, the most recent addition to the ozone monitoring requirements in 40 C.F.R. 58, are subsets of the SLAMS. On February 12, 1993, the U.S. EPA promulgated rules to establish enhanced ambient monitoring networks for ozone and ozone precursors as required by Section 182 (c)(1) of the 1990 Clean Air Act Amendments. The PAMS networks are currently required in the following 22 ozone nonattainment areas designated as serious, severe, and extreme with respect to the current 1-hour ozone NAAQS:

Beaumont-Port Arthur, TX	Portsmouth-Dover-Rochester, NH-ME

Southeast Desert Modified AQMA, CA	Baton Rouge, LA

El Paso, TX	Springfield, MA

Ventura County, CA	Milwaukee-Racine, WI

Providence-Pawtucket-Fall River, RI-MA	Sacramento, CA

Atlanta, GA	Baltimore, MD

Boston-Lawrence-Worcester, MA-NH	Chicago-Gary-Lake County (IL), IL-
IN-WI

Greater Connecticut, CT	Houston-Galveston-Brazoria, TX

Los Angeles-South Coast Air Basin, CA	San Diego, CA

New York-New Jersey-Long Island, NY-NJ-CT	Philadelphia-Wilmington-Trenton, PA-NJ-DE-MD

San Joaquin Valley, CA	Washington, DC-MD-VA

These monitoring stations collect ambient air measurements for a target list of approximately 60 volatile organic compounds (VOC) including several carbonyls, as well as oxides of nitrogen, ozone, and both surface (10m) and upper air (one site minimum per area) meteorological measurements. The Rule allows a 5-year transition or phase-in schedule for the program at a rate of at least one station per area per year.

The PAMS requirements are designed to provide as much information as practicable on the roles of ozone precursors, pollutant transport, and local meteorology in the photochemical process as well as to establish a feedback loop as a "reality check" on proposed ozone control (State Implementation Plan or SIP) strategies. Eventually, the PAMS will provide a data base for evaluating the success of the control programs and developing mid-course strategy corrections. Specific provisions of the Rule require the establishment and operation of up to five PAMS in each affected area, depending on the population of the area (See Figure 4.1.2 for a large area example). Those stations are identified as follows:

Site #1 - Characterizes upwind background and transported ozone/precursor concentrations entering the area and identifies those areas which are subjected to pollutant transport. The #1 Sites are located in the predominant morning upwind direction from the local area of maximum emissions and at a distance sufficient to obtain urban scale measurements.

Site #2 - Monitors the magnitude and type of emissions in the zone where maximum precursor emissions representative of the affected area are expected to impact. The #2 Sites are located immediately downwind (using the same morning wind direction for locating Site #1) of the area of maximum emissions and are typically placed near the downwind boundary of the central business district to obtain neighborhood scale measurements representative of the area. Additionally, a second #2 Site in the second-most predominant morning wind direction is required for larger areas.

Site #3 - Monitors the maximum ozone concentrations which occur downwind from the area of maximum emissions. Locations are chosen so that urban scale measurements are obtained. Typically, sites are located in the predominant afternoon downwind direction from the local area of maximum precursor emissions at a distance sufficient to obtain urban scale measurements.

Site #4 - Quantifies the extreme downwind pollutant concentrations which exit the area and identifies those areas which are potentially contributing to transport into other areas. The #4 Sites are located in the predominant afternoon downwind direction from the local area of maximum precursor emissions at a distance sufficient to obtain urban scale measurements.

The PAMS requirements affect those State air pollution control agencies having designated serious, severe, or extreme ozone nonattainment areas (with respect to the current 1-hour ozone NAAQS) within their jurisdictions. States are required to collect data not only to determine compliance with a National Ambient Air Quality Standard (NAAQS), but also to provide fundamental data which will help solve the ozone problem. According to the Act, the States are subsequently required to adopt and implement a program to improve ambient monitoring and emissions programs for the selected compounds. Accordingly, each State was required to submit a PAMS network description by August 12, 1993, and a revision to their SIP by November 12, 1993.

The first official year of implementation for PAMS was 1994. The implementation process was planned so that as a minimum, an area could establish one site per year; this plan would result in the network being completed by the summer of 1998. When completed, it is expected that the national PAMS network will encompass approximately 100 active sites, an increase from 38 during 1994, the first official year. Note, however, that many agencies chose to begin implementing their networks as early as 1993 during which sampling was initiated at 17 sites. With the help of §105 grant funding, the States have accelerated the installation of PAMS to capture near-term changes in the atmosphere due to the implementation of ozone control strategies.

EPA believes that the data gathered by PAMS will greatly enhance the ability of State and Local air pollution control agencies to effectively evaluate ozone nonattainment conditions and identify cost-effective control strategies. Further, the Agency anticipates that the measurements will be of substantial value in verifying ozone precursor emission inventories and in corroborating area-wide emission reductions. The data will be used to evaluate, adjust, and provide input to the photochemical grid models utilized by the States to develop ozone control strategies and demonstrate their success. The PAMS will provide information to evaluate population exposure, expand the data base available to confirm attainment/nonattainment decisions, and develop ambient ozone and ozone precursor trends. Locations of current PAMS are shown in Figure 4.1.3.

Intensive Field Studies PAMS is the first national program requiring continuous, speciated VOC measurements. Since the program is still undergoing implementation, only very limited data analyses have been perfromed. Most of our knowledge regarding ozone precursors is based on several intensive field studies and research programs discussed in Section 4.2??.

4.1.1.2	Ozone and precursor measurement methods

[to be completed....major need to discuss methods...issues etc.]

[sources PAMS TAD; NAS report; atm. Chem texts]

Regulatory overview. All forms currently being discussed for either the primary or secondary ozone NAAQS require that hourly data be available in order to calculate 8-hour and/or seasonal ozone values used to ascertain an area's attainment status. Therefore, the current Federal Reference Method for ozone monitoring as listed within 40 C.F.R. 50, and the equivalent methods as approved under 40 C.F.R. 53 are still appropriate for use under any of the proposed ozone NAAQS scenarios. The docket XX-XX-XX associated with this Advanced Notice of Proposed Rulemaking contains a listing of the currently approved U.S.EPA reference and equivalent methods. Monitoring and analysis techniques used to determine concentrations of ozone precursors as directed within the PAMS program are described within the "Photochemical Assessment Monitoring Stations Implementation Manual," EPA-454/B-93-051, March 1994, available through the National Technical Information Services (NTIS publication number PB 94 187 382), 5825 Port Royal Road, Springfield, VA 22161.

4.1.1.2.1	Ozone and CO instrumentation

4.1.1.1.2	NOx and NOy

4.1.1.1.3	VOCs

4.1.1.1.4	Radicals, peroxides and others (research grade)