Aerosol and precipitation chemistry in the southwestern United States: Spatiotemporal trends and interrelationships

Armin Sorooshian, T. Shingler, A. Harpold, C. W. Feagles, Thomas Meixner, Paul Brooks

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Abstract

This study characterizes the spatial and temporal patterns of aerosol and precipitation composition at six sites across the United States Southwest between 1995 and 2010. Precipitation accumulation occurs mostly during the wintertime (December-February) and during the monsoon season (July-September). Rain and snow pH levels are usually between 5-6, with crustal-derived species playing a major role in acid neutralization. These species (Ca2+, Mg2+, K+, Na+) exhibit their highest concentrations between March and June in both PM2.5 and precipitation due mostly to dust. Crustal-derived species concentrations in precipitation exhibit positive relationships with SO42-, NO3-, and Cl-, suggesting that acidic gases likely react with and partition to either crustal particles or hydrometeors enriched with crustal constituents. Concentrations of particulate SO42- show a statistically significant correlation with rain SO42- unlike snow SO42-, which may be related to some combination of the vertical distribution of SO 42- (and precursors) and the varying degree to which SO42-enriched particles act as cloud condensation nuclei versus ice nuclei in the region. The coarse : fine aerosol mass ratio was correlated with crustal species concentrations in snow unlike rain, suggestive of a preferential role of coarse particles (mainly dust) as ice nuclei in the region. Precipitation NO3-: SO42- ratios exhibit the following features with potential explanations discussed: (i) they are higher in precipitation as compared to PM2.5; (ii) they exhibit the opposite annual cycle compared to particulate NO3-: SO42- ratios; and (iii) they are higher in snow relative to rain during the wintertime. Long-term trend analysis for the monsoon season shows that the NO3-: SO42- ratio in rain increased at the majority of sites due mostly to air pollution regulations of SO42- precursors.

Original languageEnglish (US)
Pages (from-to)7361-7379
Number of pages19
JournalAtmospheric Chemistry and Physics
Volume13
Issue number15
DOIs
StatePublished - 2013

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precipitation (chemistry)
aerosol
snow
monsoon
acid neutralization
dust
ice
cloud condensation nucleus
trend analysis
annual cycle
vertical distribution
atmospheric pollution
rain
trend
gas
particle

ASJC Scopus subject areas

  • Atmospheric Science

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Aerosol and precipitation chemistry in the southwestern United States : Spatiotemporal trends and interrelationships. / Sorooshian, Armin; Shingler, T.; Harpold, A.; Feagles, C. W.; Meixner, Thomas; Brooks, Paul.

In: Atmospheric Chemistry and Physics, Vol. 13, No. 15, 2013, p. 7361-7379.

Research output: Contribution to journalArticle

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