- Volumes 84-95 (2024)
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Volumes 72-83 (2023)
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Volume 83
Pages 1-258 (December 2023)
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Volume 82
Pages 1-204 (November 2023)
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Volume 81
Pages 1-188 (October 2023)
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Volume 80
Pages 1-202 (September 2023)
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Volume 79
Pages 1-172 (August 2023)
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Volume 78
Pages 1-146 (July 2023)
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Volume 77
Pages 1-152 (June 2023)
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Volume 76
Pages 1-176 (May 2023)
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Volume 75
Pages 1-228 (April 2023)
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Volume 74
Pages 1-200 (March 2023)
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Volume 73
Pages 1-138 (February 2023)
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Volume 72
Pages 1-144 (January 2023)
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Volume 83
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Volumes 60-71 (2022)
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Volume 71
Pages 1-108 (December 2022)
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Volume 70
Pages 1-106 (November 2022)
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Volume 69
Pages 1-122 (October 2022)
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Volume 68
Pages 1-124 (September 2022)
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Volume 67
Pages 1-102 (August 2022)
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Volume 66
Pages 1-112 (July 2022)
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Volume 65
Pages 1-138 (June 2022)
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Volume 64
Pages 1-186 (May 2022)
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Volume 63
Pages 1-124 (April 2022)
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Volume 62
Pages 1-104 (March 2022)
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Volume 61
Pages 1-120 (February 2022)
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Volume 60
Pages 1-124 (January 2022)
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Volume 71
- Volumes 54-59 (2021)
- Volumes 48-53 (2020)
- Volumes 42-47 (2019)
- Volumes 36-41 (2018)
- Volumes 30-35 (2017)
- Volumes 24-29 (2016)
- Volumes 18-23 (2015)
- Volumes 12-17 (2014)
- Volume 11 (2013)
- Volume 10 (2012)
- Volume 9 (2011)
- Volume 8 (2010)
- Volume 7 (2009)
- Volume 6 (2008)
- Volume 5 (2007)
- Volume 4 (2006)
- Volume 3 (2005)
- Volume 2 (2004)
- Volume 1 (2003)
• Homogeneous reactions between NH3 and HNO3 govern NO3− formation in clean periods.
• Heterogeneous hydrolysis of N2O5 with high relative humidities dominant in heavy pollution process.
• Neutralization reaction caused by NH3 plays an important role in nitrate formation.
• Vehicle restrictions could effectively reduce NH3 and NO2 emissions.
With the strengthened controls on SO2 emissions and extensive increases in motor vehicles’ exhaust, aerosol pollution shifts from sulfate-rich to nitrate-rich in recent years in Xi'an, China. To further gain insights into the factors on nitrate formation and efficiently mitigate air pollution, highly time-resolved observations of water-soluble inorganic ions (WSIIs) in PM2.5 were measured in a suburban area of Xi'an, China during wintertime. Hourly concentration of total WSIIs is 39.8 μg m−3 on average, accounting for 50.3% of PM2.5 mass. In contrast to a slight decrease in the mass fraction of SO42−, NO3− shows a significant increase of the PM2.5 contribution with the aggravation of aerosol pollution. This suggests the importance of NO3− formation to haze evolution. Furthermore, homogeneous reactions govern the formation of NO3−, while alkali metals such as calcium and sodium play an additional role in retaining NO3− in PM2.5 during clean periods. However, the heterogeneous hydrolysis reaction contributed more to NO3− formation during the pollution periods under high relative humidity. Our investigation reveals that temperature, relative humidity, oxidant, and ammonia emissions facilitate rapid NO3− formation. Using the random forest (RF) model, NO3− concentrations were successfully simulated with measured variables for the training and testing datasets (R2 > 0.95). Among these variables, CO, NH3, and NO2 were found to be the main factors affecting the NO3− concentrations. Compared with the period without vehicle restriction, the contributions of NO3− and NH4+ to PM2.5 mass decreased by 5.3% and 3.4% in traffic restriction periods, respectively. The vehicle restriction leads to the decreases of precursor gases of NO2, SO2, and NH3 by 12.8%, 5.9%, and 27.6%, respectively. The results demonstrate collaborative emission reduction of NOx and NH3 by vehicle restrictions, and using new energy vehicles (or electric vehicles) can effectively alleviate particulate matter pollution in northwest China.