Enhanced Monitoring in Major Metropolitan Areas


Photochemical Assessment Monitoring Stations

The 1990 Federal Clean Air Act Amendments required additional monitoring of ozone and of the pollutants that combine to form ozone-nitrogen oxides and volatile organic compounds. In response, EPA provided funds for state and local agencies to establish the Photochemical Assessment Monitoring Stations (PAMS) program.

In 1993, air pollution control agencies in the Mid-Atlantic Region began to set up and operate new, state of the art monitoring stations as part of the national PAMS program. PAMS networks are required in all serious and severe ozone nonattainment areas. The PAMS network is expected to be complete by 1998.

PAMS sites measure ozone, nitrogen oxides, nearly 60 volatile organic compounds, and both surface and upper-air weather data. Some sites also measure selected toxic air pollutants.

Up to five PAMS sites are required for each serious or severe nonattainment area. Because nonattainment areas in the Mid-Atlantic Region are close to each other, PAMS sites may serve as part of more than one area's network. For example, the Lums Pond si te in Delaware is part of the PAMS network for Philadelphia, for Baltimore, and for Washington, DC.

PAMS sites are classified into four types:

Sources: EPA (1996), National Air Quality and Emissions Trends Report, 1995, EPA 454/R-96-005, Office of Air Quality Planning and Standards, Research Triangle Park, NC.
EPA (1996), Photochemical Assessment Monitoring Stations, 1996 Data Analysis Results Report.
Nash Gerald and Mark Schmidt, "Photochemical Assessment Monitoring: Overview and Data Analysis Activities."

Table:
Photochemical Assessment Monitoring Stations 49 Areas that Have Met Air Quality Standards and Been Redesignated as Attainment


Measurement of Specific Volatile Organic Compounds

The volatile organic compounds measured individually at PAMS sites (targeted VOCs) do not account for the total amount of hydrocarbons in the air. For example, at the McMillan Reservoir site in the District of Columbia, targeted V OCs accounted for just over half of the total hydrocarbons. At the Clifton Park site in Maryland and Rider University in New Jersey, about 75% of the total hydrocarbons were accounted for by individual VOC measurements. The targeted VOCs are measurable indicators of major VOC sources.

Chart: Fraction of TNMHC Accounted for by Targeted and Non-Targeted Compounds at Selected MARAMA PAMS Sites During the 1995 Summer Morning Hours


Most Prevalent Volatile Organic Compounds

Average 1995 summer morning Concentrations of the specific volatile organic compounds measured at PAMS sites are plotted on the following charts. There is quite a bit of variation between the charts. (See Appendix D for data used to create these charts.)

Each chart also identifies the "top 10" specific compounds in two ways. First, there is a list of the ten compounds with the highest average concentration for each site. Second, there is a list of the ten compounds that are the highest considering both the average concentration and the reactivity of the compound.

The targeted VOCs that are the most abundant by concentration alone are listed below along with typical sources of these VOCs. These VOCs were also among the most abundant identified in the northeastern US in 1994, in Los Angeles in 1987, and in a 1984 s tudy of five cities.

Isopentane Gasoline vapors
Propane LPG or natural gas use
Toluene Motor vehicle exhaust, graphic arts/surface coating industry
Ethane Natural gas use
n-Pentane Gasoline vapors

Highly reactive compounds form ozone more easily than less reactive compounds. EPA calculated the reactivity of the compounds using the Maximum Incremental Reactivity (MIR) scale published in 1994 by William Carter of the University of California. Of th e targeted VOCs, the most important when considering reactivity as well as Concentrations are:

Ethylene Motor vehicle exhaust
Isoprene Natural emissions
Propylene Motor vehicle exhaust
m & p Xylenes Gasoline evaporation and motor vehicle exhaust
1,2,4-trimethylbenzene Gasoline evaporation and motor vehicle exhaust

Consistent with emissions estimates shown earlier in this Atlas, motor vehicle exhaust, gasoline vapors, and natural emissions are indicated by the top compounds. As noted above, PAMS target compounds do not represent all VOCs present in the air, but the y are indicative of major sources affecting the area.

Sources: Mark Schmidt of EPA's Office of Air Quality Planning and Standards prepared these charts based on data in EPA's AIRS system.
Preview of 1994 Ozone Precursor Concentrations in the Northeastern US, (1995) Northeast States for Corrdinated Air Use Management (Ambient Monitoring and Assessment Committee), with assistance from EPA New Engl and, August.
W.P.L. Carter, (1994) Development of ozone reactivity scales for volatile organic compounds. J. Air & Waste Managment Association, 44, 881-889.
Information concerning typical sources of target compounds comes from three sources:
T. Pace, M. Schmidt, and C. Wayland, (1996) Chapter 3, EPA Photochemical Assessment Monitoring Stations, 1996 Data Analysis Results Report, EPA-454/R-96-006, October.
H. Main, P. Roberts, and M. Korc, (1996) PAMS Data Analysis Workshop, (notebook), Presented at EPA Region III Headquarters, Philadelphia, prepared for US Environmental Protection Agency Office of Air Quality Pl anning and Standards, July.
M. Korc, Sonoma Technology, Inc., personal communication, February 1997.

Chart: 1995 Summer Morning (6-9 am) Average Concentrations for PAMS Targeted VOC Species at Lums Pond, DE

Chart: 1995 Summer Morning (6-9 am) Average Concentrations for PAMS Targeted VOC Species at McMillan Reservoir, RC, DE

Chart: 1995 Summer Morning (6-9 am) Average Concentrations for PAMS Targeted VOC Species at Clifton Park, MD

Chart: 1995 Summer Morning (6-9 am) Average Concentrations for PAMS Targeted VOC Species at Rider University, NJ

Chart: 1995 Summer Morning (6-9 am) Average Concentrations for PAMS Targeted VOC Species at Philadelphia City Lab, PA

Chart: 1995 Summer Morning (6-9 am) Average Concentrations for PAMS Targeted VOC Species at Corbin, VA


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Last revised: 11/17/98