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New Hampshire Department of Environmental Services


In accordance with the 1990 Clean Air Act Amendments, the Environmental Protection Agency (EPA) set forth requirements for more extensive ozone and ozone precursor monitoring in areas where levels were considered to be non-attainment. In these areas, the States have established ambient air monitoring sites called Photochemical Assessment Monitoring Stations (PAMS).

At PAMS sites, NHDES collects and reports detailed data for volatile organic compounds, nitrogen oxides, ozone, and meteorological parameters.  Each year NHDES collects PAMS data on an hourly basis from June through September and analyzes the results during the off season. Analyses of these data are helping the EPA and the States better understand the underlying causes of ozone pollution, develop effective remedies, and measure environmental improvement.

PAMS Stations

NHDES is responsible for the operation of two Photochemical Assessment Monitoring Stations in the state: one on the summit of Pack Monadnock Mountain (2288-foot elevation) at Miller State Park in Peterborough and the other at the Moose Hill School in Londonderry. The combination of the two sites provides a unique high-low look at ozone precursors in the skies above New Hampshire.

Outline map of the U.S.   Map of NH

In 2015, the Londonderry site replaced the Gilson Road site in Nashua, which had been operating since 2005. This move was driven by a desire to gather as much data as possible at a single site. The Londonderry site is one of two NCORE stations in New Hampshire; the other is on Pack Monadnock.  NCORE stations are part of a national multi-pollutant network monitoring plan integrating several advanced measurement systems for particulate matter, pollutant gases, and meteorological parameters. Pack Monadnock previously measured NCORE and PAMS parameters.  As of the 2015 PAMS move to Londonderry, NHDES measures all these parameters at Londonderry as well.

Data Collection

The PAMS program uses thermal desorption and gas chromatography to analyze for 57 different Volatile Organic Compounds (VOCs) in ambient air (see compound list in Table #1 below). These VOCs are known ozone precursors; in the presence of sunlight and NOx, they can combine to form ground-level ozone. Ozone is a pollutant of primary concern within the region.

PAMS Gas Chromatography Analyzer

PAMS gas chromatography analyzer


Table 1: PAMS Parameters with AIRS Code

AIRS Number Compound   AIRS Number Compound
43202 Ethane   43960 2-Methylheptane
43203 Ethylene   43253 3-Methylheptane
43204 Propane   43233 n-Octane
43205 Propylene   45203 Ethylbenzene
43214 Isobutane   45109 m&p-Xylene
43212 n-Butane   45220 Styrene
43206 Acetylene   45204 o-Xylene
43216 trans-2-Butene   43235 n-Nonane
43280 1-butene   45210 Isopropylbenzene
43217 cis-2-Butene   45209 n-Propylbenzene
43242 Cyclopentane   45212 m-Ethyltoluene
43221 Isopentane   45213 p-Ethyltoluene
43220 n-Pentane   45207 1,3,5-Trimethylbenzene
43226 trans-2-Pentene   45211 o-Ethyltoluene
43224 1-Pentene   45208 1,2,4-Trimethylbenzene
43227 cis-2-Pentene   43238 n-Decane
43244 2,2-Dimethylbutane   45225 1,2,3-Trimethylbenzene
43284 2,3-Dimethylbutane   45218 m-Diethylbenzene
43285 2-Methylpentane   45219 p-Diethylbenzene
43230 3-Methylpentane   43954 n-Undecane
43243 Isoprene   43102 Total Non-Methane Organic Compounds
43231 n-Hexane   43000 Sum PAMS Target Species
43262 Methylcyclohexane   44201 Ozone
43247 2,4-Dimethylpentane   42601 Nitric Acid
45201 Benzene   42602 Nitrogen Dioxide
43248 Cyclohexane   42603 Oxides of Nitrogen
43263 2-Methylhexane   62101 Temperature
43291 2,3-Dimethylpentane   61101 Wind Speed
43249 3-Methylhexane   61102 Wind Direction
43250 2,2,4-Trimethylpentane   62201 Relative Humidity
43232 n-Heptane   63301 Solar Radiation*
43261 Methylcyclohexane   63302 UV Radiation*
43252 2,3,4-Trimethylpentane   64101 Barometric Pressure
45202 Toluene   65102 Precipitation

* Required at only one PAMS site per area (Pack Monadnock)

Analysis and Reporting

NHDES analyzes PAMS data during the off season. PAMS data analysis consists of trends, diurnal patterns, meteorological comparisons, and a discussion of findings. For more detailed information, please open the most recent annual data reports under Publications.

Graph #1 below depicts the average PAMS compound trends at the PAMS sites operating through 2015 (Pack Monadnock, Nashua and Londonderry). There is generally a downward trend despite slight yearly fluctuations. Meteorological conditions such as rainfall and wind direction play a significant role in these yearly fluctuations. Additionally, data is influenced by infrequent local influences. For example, a paving project near the Nashua site in 2009 biased the data high that year. These sites have relatively little history with regard to VOC data, so further monitoring will continue to give us a clearer picture of trends and the local changes affecting the data.

Average PAMS compund comparisoin Miller State Park and Gilson Road


NH Department of Environmental Services | 29 Hazen Drive | PO Box 95 | Concord, NH 03302-0095
(603) 271-3503 | TDD Access: Relay NH 1-800-735-2964 | Hours: M-F, 8am-4pm

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