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.
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.
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.
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
Table 1: PAMS Parameters with AIRS Code
|AIRS Number||Compound||AIRS Number||Compound|
|43243||Isoprene||43102||Total Non-Methane Organic Compounds|
|43231||n-Hexane||43000||Sum PAMS Target Species|
|43248||Cyclohexane||42603||Oxides of Nitrogen|
* 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 2014 (Pack Monadnock and Nashua). The trend at both sites is downward, though much more so on Pack Monadnock than in Nashua. Meteorological conditions such as rainfall and wind direction play a significant role in the 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.