The effect of acidity variations in cloud droplet populations on aqueous-phase sulfate production
- Carnegie Mellon Univ., Pittsburg, PA (United States)
The majority of global atmospheric sulfate production occurs in clouds. Experimental evidence suggests that significant chemical heterogeneities exist in cloud droplet populations. Both theoretical and field studies suggest that the acidity of a cloud droplet population can differ by 1 pH unit or more between the smallest and largest droplets. Traditionally, cloud chemistry has been studied using bulk models that assume that the aqueous- phase chemistry can be accurately modeled using {open_quotes}mean droplet{close_quotes} properties. The average droplet population pH is then used as the basis for calculating reaction rates. Using this bulk chemistry approach in cloud or fog models may lead to significant errors in the predicted aqueous-phase reaction rates. We prove analytically that the use of a droplet Population`s average pH always results in the underestimation of the rate of sulfate production. In order to examine the magnitude of this error, we have developed two aqueous-phase chemistry models: a droplet size-resolved model and a bulk chemistry model. The discrepancy between the results of these two models indicates the degree of error introduced by assuming bulk aqueous-phase properties. The magnitude of this error depends on the availability of SO{sub 2}, H{sub 2}O{sub 2}, NH{sub 3}, and acidity, and can range from zero to a factor of three for reasonable ambient conditions. A modeling approach that combines the accuracy of the size-resolved model and the low computing requirements of the bulk model is developed.
- OSTI ID:
- 166529
- Report Number(s):
- CONF-9510126-; TRN: 95:008181-0020
- Resource Relation:
- Conference: Annual meeting of the American Association for Aerosol Research, Pittsburgh, PA (United States), 9-13 Oct 1995; Other Information: PBD: 1995; Related Information: Is Part Of American Association for Aerosol Research (AAAR) `95; PB: 464 p.
- Country of Publication:
- United States
- Language:
- English
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