Spatial and seasonal variability of PM2.5 acidity at two Chinese megacities: insights into the formation of secondary inorganic aerosols
Open Access
- 6 February 2012
- journal article
- research article
- Published by Copernicus GmbH in Atmospheric Chemistry and Physics
- Vol. 12 (3), 1377-1395
- https://doi.org/10.5194/acp-12-1377-2012
Abstract
Aerosol acidity is one of the most important parameters influencing atmospheric chemistry and physics. Based on continuous field observations from January 2005 to May 2006 and thermodynamic modeling, we investigated the spatial and seasonal variations in PM2.5 acidity in two megacities in China, Beijing and Chongqing. Spatially, PM2.5 was generally more acidic in Chongqing than in Beijing, but a reverse spatial pattern was found within the two cities, with more acidic PM2.5 at the urban site in Beijing whereas the rural site in Chongqing. Ionic compositions of PM2.5 revealed that it was the higher concentrations of NO3− at the urban site in Beijing and the lower concentrations of Ca2+ within the rural site in Chongqing that made their PM2.5 more acidic. Temporally, PM2.5 was more acidic in summer and fall than in winter, while in the spring of 2006, the acidity of PM2.5 was higher in Beijing but lower in Chongqing than that in 2005. These were attributed to the more efficient formation of nitrate relative to sulfate as a result of the influence of Asian desert dust in 2006 in Beijing and the greater wet deposition of ammonium compared to sulfate and nitrate in 2005 in Chongqing. Furthermore, simultaneous increase of PM2.5 acidity was observed from spring to early summer of 2005 in both cities. This synoptic-scale evolution of PM2.5 acidity was accompanied by the changes in air masses origins, which were influenced by the movements of a subtropical high over the northwestern Pacific in early summer. Finally, the correlations between [NO3−]/[SO42−] and [NH4+]/[SO42−] suggests that under conditions of high aerosol acidity, heterogeneous reactions became one of the major pathways for the formation of nitrate at both cities. These findings provided new insights in our understanding of the spatial and temporal variations in aerosol acidity in Beijing and Chongqing, as well as those reported in other cities in China.This publication has 73 references indexed in Scilit:
- Ambient sulfur dioxide, nitrogen dioxide, and ammonia at ten background and rural sites in China during 2007–2008Atmospheric Environment, 2010
- Size-resolved aerosol water-soluble ionic compositions in the summer of Beijing: implication of regional secondary formationAtmospheric Chemistry and Physics, 2010
- Highly time- and size-resolved characterization of submicron aerosol particles in Beijing using an Aerodyne Aerosol Mass SpectrometerAtmospheric Environment, 2010
- Comparison of thermodynamic predictions for in situ pH in PM2.5Atmospheric Environment, 2006
- Characteristics of aerosol acidity in Hong KongAtmospheric Environment, 2004
- Chemical characterization of ambient aerosol collected during the southwest monsoon and intermonsoon seasons over the Arabian Sea: Anions and cationsJournal of Geophysical Research: Atmospheres, 1999
- Global concentrations of tropospheric sulfate, nitrate, and ammonium aerosol simulated in a general circulation modelPublished by American Geophysical Union (AGU) ,1999
- Relationships among aerosol constituents from Asia and the North Pacific during PEM‐West AJournal of Geophysical Research: Atmospheres, 1996
- General circulation model assessment of the sensitivity of direct climate forcing by anthropogenic sulfate aerosols to aerosol size and chemistryPublished by American Geophysical Union (AGU) ,1995
- Modes in the size distributions of atmospheric inorganic aerosolAtmospheric Environment. Part A. General Topics, 1990