A re-evaluation of sulfur budgets, lifetimes, and scavenging ratios for eastern North America

Lifetimes, scavenging ratios, and budgets describe the cycling of atmospheric constituents and are often used in formulating air pollution control strategies. Most previous studies of sulfur lifetimes, budgets, and scavenging ratios have been based on limited observational data or data from highly simplified models. The Regional Acid Deposition Model (RADM2.61) shows some skill in predicting atmospheric mixing ratios of acidic materials and other related trace constituents and acid deposition patterns in North America, and so, analysis of its established, theoretical, database serves as a counterpoint to previous studies of sulfur budgets, Lifetimes, and scavenging ratios. The annual budget shows that the net transport (outflow minus inflow) of sulfur compounds out of eastern North America is equal to the total deposition within the domain. Of the total deposition, 63% is from wet deposition and 37% is from dry deposition. The annual average lifetime of sulfur dioxide (38 hours), estimated by the turnover time, is limited by aqueous conversion, while that for sulfate aerosols (54 hours) is limited by their removal in precipitation. The annual average lifetime of sulfur in this domain is slightly more than three days. Episodic lifetimes and budgets, based on particular synoptic situations, show large variations around the annual values. Episodic precipitation scavenging ratios exhibit similar variability and are used to offer explanations of several potential biases found in the wet sulfur deposition amounts as predicted by the EMEP sulfur transport model and other published results.