Co-Occurrence Patterns of Gaseous Air Pollutant Pairs at Different Minimum Concentrations in the United States (Journal Version)

摘要

The frequency of co-occurrences for SO2/NO2, SO2/O3 and O3/NO2 at rural and remote monitoring sites in the United States was characterized for the months of May-September for the years 1978-1982. Minimum hourly concentrations of 0.03 and 0.05 ppm of each gas were used as the criteria for defining a 'co-occurrence.' The objectives of the study were to: (1) identify the types of co-occurrence patterns and their frequency; (2) identify whether the frequency of hourly simultaneous co-occurrences increased substantially when the minimum concentration was lowered (e.g., from 0.05 to 0.03 ppm) for each pollutant; and (3) determine whether the frequency of co-occurrences showed large year-to-year variation. Based on their observations, researchers attempting to assess the potential effects of SO2/NO2, SO2/O3 and O3/NO2 in the United States should construct simulated exposure regimes so that (1) hourly simultaneous and daily simultaneous-only co-occurrences are fairly rare and (2) when co-occurrences are present, complex-sequential and sequential-only co-occurrence patterns predominate. (Copyright (c) 1987 Pergamon Journals Ltd.)