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Richard C. Easter
and
Leonard K. Peters

Abstract

Binary homogeneous nucleation of sulfuric acid and water vapor is thought to be the primary source of new particles in the marine atmosphere. The rate of binary homogeneous nucleation depends strongly on temperature and the gas-phase concentrations of both sulfuric acid and water vapor. This paper investigates the effects of these nonlinear dependencies on the rate of formation of new particles. An increase of 2°-3°C can reduce the particle formation rate by an order of magnitude. Large-scale fluctuations such as those characteristic of a well-mixed boundary layer can alternately “turn on” and “shut off” the nucleation process, giving rise to regions of new particle formation that are quite localized. These “bursts” of nucleation correspond to higher altitudes in the boundary layer. Small-scale fluctuations, more typical of normal atmospheric turbulence, can increase the binary homogeneous nucleation rate severalfold above the rate calculated based on mean conditions.

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James L. Vance
and
Leonard K. Peters

Abstract

The atmospheric reaction between ammonia and sulfur dioxide is reconsidered in light of recent experimental studies. A mechanism is proposed that presumes the existence of the intermediate gas phase species NH3·SO2, prior to their nucleation and aerosol formation. Based on this mechanism and data obtained by other investigators, the vapor pressures of the solid compounds formed are estimated to be on the order of 10−4 to 10−7 torr. Thus, it is suggested that this process should not yet be dismissed as a possible route in the formation of atmospheric sulfate aerosols.

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Toshihiro Kitada
,
Gregory R. Carmichael
, and
Leonard K. Peters

Abstract

The characteristics of the transport of chemically reactive species under land- and sea-breeze (LSB) circulations are investigated using a detailed transport/chemistry model, which includes 84 gas-phase and 10 heterogeneous chemical reactions. Model applications are presented which use flow fields derived from a modified version of the Asai and Mitsumoto model and eddy diffusivity profiles predicted by the boundary-layer model of Yamada and Mellor as inputs. The effects of nonprecipitating clouds associated with the LSB circulation on the calculated concentration fields are also studied.

Mass transports by updrafts and counterflows associated with the LSB circulation and diurnally varying eddy diffusion processes show transitions between double and single maxima within a 24-hour cycle. The vertical profiles of some secondary pollutants such as O3 generally agree with field observations. Clouds are also shown to affect the predicted distributions of both the soluble and less soluble species by reducing the below-cloud photon flux, by removing soluble species from the air at cloud level, and/or by in-cloud production processes. Deposition processes reduce the species concentrations near the surface, and these effects propagate upward through mass transport processes. However, the qualitative characteristic vertical concentration profiles are similar to the cases where deposition is not included. Finally, the results demonstrate the effectiveness of the divergence correction method used in the numerical calculations in eliminating the fictitious production and consumption reactions introduced by nonzero divergence wind fields.

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