Central California Ozone Study (CCOS) - Desert Research Institute

CCOS Field Operations Plan Version 2: 5/31/00
2.3.1 Criteria Pollutant Air Monitoring Stations
The California Air Resources Board and local air pollution control districts currently
operate 185 air quality monitoring stations throughout northern and central California. Of the
active sites, 130 measure ozone and 76 measure NOx. Carbon monoxide and hydrocarbons are
measured at 57 and 11 sites, respectively. Data from these sites are routinely acquired and
archived by the ARB and Districts. This extensive surface air quality monitoring network
provides a substantial database for setting initial condition for the model, and for operational
evaluation of model outputs. ARB, in collaboration with the California air quality management
districts, is establishing the PM 2.5 monitoring sites. The existing PM 10 acquires filter samples
every sixth day. Several of the PM 10 sites have continuous monitors that measure hourly PM 10
everyday. Watson et al. (1998) describes the PM measurement network.
2.3.2 Photochemical Assessment Monitoring Stations
Under Title I, Section 182, of the 1990 Amendments to the Federal Clean Air Act, the
EPA proposed the implementation of a national network of enhanced ambient air monitoring
stations. States with areas classified as serious, severe, or extreme for ozone attainment are
required to establish photochemical assessment monitoring stations (PAMS) as par of their State
Implementation Plan. Each station measures speciated hydrocarbons and carbonyl compounds,
ozone, oxides of nitrogen, and surface meteorological data. Additionally, each area must monitor
upper air meteorology at one representative site.
The program was phased in over a five-year schedule, beginning in 1994 at a rate of at
least one station per year. A maximum of five PAMS sites are required in affected nonattainment
areas, depending on the population of the Metropolitan Statistical Area/Consolidated
Metropolitan Statistical Area (MSA/CMSA) or nonattainment area, whichever is larger. PAMS
networks are based on selection of an array of site locations relative to ozone precursor source
areas and predominant wind directions associated with high ozone events. Specific monitoring
objectives associated with each of these sites result in four distinct site types.
Type 1 sites are established to characterize upwind background and transported ozone
and its precursor concentrations entering the area and to identify those areas that are subjected to
overwhelming transport. Type 1 sites are located in the predominant morning upwind direction
from the local area of maximum precursor emissions during the ozone season. Typically, Type 1
sites will be located near the edge of the photochemical grid model domain in the predominant
upwind direction from the city limits or fringe of the urbanized area.
Type 2 sites are established to monitor the magnitude and type of precursor emissions in
the area where maximum precursor emissions are expected. These sites also are suited for the
monitoring of urban air toxic pollutants. Type 2 sites are located immediately downwind of the
area of maximum precursor emissions and are typically placed near the downwind boundary of
the central business district. Additionally, a second Type 2 site may be required depending on the
size of the area, and will be placed in the second-most predominant morning wind direction.
Chapter 2: FIELD MEASUREMENTS 2-4