Transport of sulfur oxides within the Los Angeles sea breeze/land breeze circulation system

The sea breeze/land breeze circulation system in the Los Angeles area results in transport of pollutants seaward at night followed by return of aged material inland the next day. This characteristic wind reversal pattern both increases the retention time available for the oxidation of SO_2 to form sulfates and causes individual air parcels to make multiple passes over large coastal emissions sources. As a result, the Los Angeles atmosphere exhibits high peak day and high annual mean sulfate concentrations in spite of the fact that sulfate concentrations in marine background or desert air are low

Convective Downmixing of Plumes in a Coastal Environment

This paper describes the results of an atmospheric tracer study in which sulfur hexafluoride (SF_6) was used to investigate the transport and dispersion of effluent from a power plant located in a coastal environment. The field study demonstrated that material emitted into an elevated stable layer at night can be transported out over the ocean, fumigated to the surface, and then he returned at ground level by the sea breeze on the next day. At night when cool stable air from the land encounters the warmer ocean convective mixing erodes the stable layer forming an internal boundary layer. When the growing boundary layer encounters an elevated plume the pollutant material, entrained at the top of the mixed layer, can be rapidly transported in ∼20 min to the surface. Various expressions for the characteristic downmixing time (λ = Z_i/w_*) are developed utilizing the gradient Richardson number, the Monin-Obukhov length and turbulence intensifies. Calculations using these expressions and the field data are compared with similar studies of convective mixing over the land

Photochemical Smog Systems: Heterogeneous Decay of Ozone

Fox et al. (1) describe the results of two experiments from which they conclude that "dilution as opposed to static experimental conditions may prove to be more important if smog chamber data are to be used as guides in developing certain future control strategies." Although the above suggestion may be correct, the evidence presented by Fox et al. (1) is incomplete in at least one serious aspect

Transport and oxidation of SO_2 in a stagnant foggy valley

The fate of SO_2 emitted in the San Joaquin Valley of California under stagnant foggy conditions was determined by the release of an inert tracer and the concurrent monitoring of SO_2 and SO_4^(2−) concentrations. At night, SO_2 was found to be trapped in a dense fog layer below a strong and persistent inversion based a few hundred meters above the valley floor. This lack of ventilation led to the accumulation of SO_2 and SO_4^(2−) over a major SO_2 source region in the valley. The rate of oxidation of SO_2 to SO_4^(2−) in fog was estimated at 3 ± 2%h^(−1). Production of acidity from the oxidation of SO_2 fully titrated the NH_3(g) present before the fog, and led to a progressive drop of the fogwater pH over the course of the night. In the afternoon, the valley was found to be efficiently ventilated by a buoyant upslope flow through the inversion. The tracer data indicated that about 40 % of the air transported upslope in the afternoon was returned to the valley in the night-time drainage flow. The fates of SO_2 and SO_4^(2−) in the valley during extended high-inversion episodes appear to depend considerably on the presence of fog or stratus, and on the extent of daytime insolation

Transport and oxidation of SO2 in a stagnant foggy valley

The fate of SO2 emitted in the San Joaquin Valley of California under stagnant foggy conditions was determined by the release of an inert tracer and the concurrent monitoring of SO2 and SO42− concentrations. At night, SO2 was found to be trapped in a dense fog layer below a strong and persistent inversion based a few hundred meters above the valley floor. This lack of ventilation led to the accumulation of SO2 and SO42− over a major SO2 source region in the valley. The rate of oxidation of SO2 to SO42− in fog was estimated at 3 ± 2%h−1. Production of acidity from the oxidation of SO2 fully titrated the NH3(g) present before the fog, and led to a progressive drop of the fogwater pH over the course of the night. In the afternoon, the valley was found to be efficiently ventilated by a buoyant upslope flow through the inversion. The tracer data indicated that about 40 % of the air transported upslope in the afternoon was returned to the valley in the night-time drainage flow. The fates of SO2 and SO42− in the valley during extended highinversion episodes appear to depend considerably on the presence of fog or stratus, and on the extent of daytime insolation.Engineering and Applied Science