The application of data from photochemical assessment monitoring stations to the observation-based model

The observation-based model – a diagnostic model designed to estimate ozone sensitivity to changes in the concentration of volatile organic compounds, nitrogen oxides, and CO – was used to analyze data gathered during the summer of 1995 at three photochemical assessment monitoring sites (PAMS). The sites were located in Washington DC, Bronx, New York, and Houston, Texas, with the first two being categorized as urban/cental city commercial and the latter as industrial/suburban. Our analysis indicated that: (i) natural hydrocarbons (primarily isoprene) represented a significant fraction of the total hydrocarbon reactivity at all three sites and significantly degraded the efficacy of VOC emission reductions as an O3 mitigation strategy; and (ii) afternoon NO concentrations at all three sites typically fell to levels at or below the limit of detection of the PAMS instrumentation and, as a result, it was not possible to determine whether O3 at the sites was more sensitive to reductions in anthropogenic hydrocarbons or nitrogen oxides.