Long-path UV spectroscopic and in-situ measurements of air pollutants in the Washington DC and Middle Atlantic regions

The EPA is preparing to issue new regulations calling for enhanced monitoring of ozone and oxides of nitrogen and additional monitoring of volatile organic compounds (VOC), including aldehydes, as well as meteorological parameters. Ozone non-attainment areas classed as serious or worse would be required to establish photochemical assessment monitoring stations (PAMS). Long path, remote sensing methods are not deemed by the EPA to be sufficiently accurate and comprehensive in providing fully speciated VOC measurements to be included in the regulations. This paper reports on the performance of a representative long path system based on ultra-violet absorption spectroscopy, and assesses the potential benefits and limitations for the future use of such systems in the PAMS network and in related air quality management applications. The basis for our assessment is field experience with a commercially available U-V spectroscopic long path instrument, using differential optical absorption spectroscopy (DOAS), as well as reference to the published experience of others using similar long path methods for measuring air pollutants. The database for our analysis consists of air quality measurements, obtained from the DOAS instrument and an existing network of point monitors (as archived in the AIRS database of EPA), in the Washington DC region during the summer of 1991. The goal of this continuing study is to suggest ways in which the long path spectroscopic methods might be used in a cost-effective manner to complement the more detailed batch sampling methods in support of urban air quality management.