Marginal PM25: Nonlinear Aerosol Mass Response to Sulfate Reductions in the Eastern United States

• Published in: Journal of the Air & Waste Management Association (1995) Vol. 49; no. 12; pp. 1415 - 1424
• Main Authors: West, J. Jason, Ansari, Asif S., Pandis, Spyros N.
• Format: Journal Article
• Language: English
• Published: Pittsburgh, PA Taylor & Francis Group 01.12.1999; Air & Waste Management Association
• Subjects: Applied sciences; Atmospheric pollution; Earth, ocean, space; Exact sciences and technology; External geophysics; Meteorology; Particles and aerosols; Pollutants physicochemistry study: properties, effects, reactions, transport and distribution; Pollution; United States; North America; America; Water; Ammonium; Pollution prevention; Nitrates; Diurnal variation; Sulfates; Pollutant emission; Time variation; Sulfur dioxide; Atmospheric interaction; Suspended particle; Fine particle; Seasonal variation; Aerosols; Air pollution; East
• ISSN: 1096-2247; 2162-2906
• DOI: 10.1080/10473289.1999.10463973

Reductions in airborne sulfate concentration may cause inorganic fine particulate matter (PM 25 ) to respond nonlinearly, as nitric acid gas may transfer to the aerosol phase. Where this occurs, reductions in sulfur dioxide (SO 2 ) emissions will be much less effective than expected at reducing PM 2.5 . As a measure of the efficacy of reductions in sulfate concentration on PM , we define marginal PM 2.5 as the local change in PM 2.5 resulting from a small change in sulfate concentration. Using seasonal-average conditions and assuming thermodynamic equilibrium, we find that the conditions for PM 2.5 to respond nonlinearly to sulfate reductions are common in the eastern United States in winter, occurring at half of the sites considered, and uncommon in summer, due primarily to the influence of temperature. Accounting for diurnal and intraseasonal variability, we find that seasonal-average conditions provide a reasonable indicator of the time-averaged PM 2.5 response. These results indicate that reductions in sulfate concentration may be up to 50% less effective at reducing the annual-average PM 2.5 than if the role of nitric acid is neglected. Further, large reductions in sulfate will also cause an increase in aerosol nitrate in many regions that are the most acidic.