ACQUISITION OF REGIONAL AIR QUALITY MODEL VALIDATION DATA FOR NITRATE, SULFATE, AMMONIUM ION AND THEIR PRECURSORS

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Abstract

An intensive field study was conducted throughout California's South Coast Air Basin to acquire air quality model validation data for use with aerosol nitrate formation models. Aerosol nitrate, sulfate, ammonium, other major ionic aerosol species, nitric acid gas and ammonia were measured concurrently at ten sites for forty-eight consecutive hours during the period 30–31 August 1982. Ozone, NO and NOx were measured at all locations, and PAN was measured at Pasadena and Riverside, completing a nitrogen balance on the air masses studied.

The product of the measured nitric acid and ammonia concentrations ranged from less than 1 ppbv2 to greater than 300 ppbv2 during the experiment, providing a wide range of conditions over which comparisons can be drawn between chemical equilibrium calculations and experimental results. The ionic material in the aerosol phase was chemically more complex than is assumed by present theoretical models for the equilibrium between NH3, HNO3 and the aerosol phase, and included significant amounts of Na+, Ca2+, Mg2+, K+ and Cl in addition to NH+4, SO2−4 and NO3. Results of the experiment showed that aerosol nitrate levels in excess of 20 μgm−3 accumulated in near-coastal locations in the morning of 31 August, followed by subsequent transport across the air basin. Trajectory analysis showed that the afternoon aerosol nitrate peak observed inland at Rubidoux near Riverside was associated with the same air mass that contained the high morning nitrate levels near the coast, indicating that description of both transport and atmospheric chemical reactions is important in understanding regional nitrate dynamics.

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