Abstract
Beijing, the capital city of China, has achieved remarkable progress in terms of an improvement in air quality under strict control policies in the past 10 years from various sources. In this paper, the characteristics of fine particulate matter (PM2.5) and O3 in January 2013 and 2018 in Beijing are discussed on the basis of daily sample analysis and hourly monitoring data. It was found that the PM2.5 pollution for the month of January in Beijing has been greatly curbed. The SO42− concentration and proportion of PM2.5 decreased, while the proportions of NO3− and NH4+ increased. Organic matter represented the major component during the two periods with the proportions of 31.7% ± 8.2% and 31.4% ± 9.8%. The results of the Hybrid Single Particle Lagrangian Integrated Trajectory (Hysplit) model and Potential Source Contribution Function (PSCF) method showed that air mass from southern nearby regions accounted for 34% and 10% in 2013 and 2018, respectively, which was closely related to the pollution period. Thus, the input direction of air mass in January 2018 was more conducive to the diffusion of pollutants. Modeling results of the Weather Research and Forecasting model (WRF) coupled with Comprehensive Air Quality Model Extensions (CAMx) indicated that the contribution of industry sources to PM2.5 and O3 decreased from 2013 to 2018, while mobile sources increased. This was mainly due to the different control policies on various emission sources. In terms of O3 sources, more control measurements should be taken on volatile organic compounds (VOCs) due to its prominent effect on O3 concentration in both periods. The reduction in emissions and the meteorological conditions both contributed effectively to the sharp decrease in PM2.5 concentration. However, the change in weather conditions had the greater impact on the decrease in PM2.5 concentration, while the reduction in emissions was weakened as a function of this change.
Highlights
It is worth noting that the total proportion of SNA during the two sampling periods was similar with values of 41.1% ± 12.3% and 41.1% ± 7.1% in 2013 and 2018, respectively
The correlation coefficient between cations and anions in the target sampling periods ranged from 0.88 to 0.95. This indicated that the combination of NH4 + with SO4 2− and NO3 − was the major form of SNA
Two sampling projects were measured in January 2013 and 2018, and daily PM2.5 samples were collected, with chemical components including water-soluble ions, carbon components, and inorganic element analyzed
Summary
Air pollution reduces atmospheric visibility [4], affects public transportation [5], and increases the incidence of cardiovascular and respiratory diseases [6,7], and affects the global climate [8]. To overcome the air pollution challenge, multiple measures have been taken by the government since 2013, including shifting the energy and construction industries, as well as regulating and shutting down “small scattered dirty” factories. The State Council issued the “Air Pollution Prevention and Control Action Plan” [12] on 13 September 2013. The governments of Beijing, Tianjin, and Hebei issued a corresponding action plan, targeting the control of the combustion of coal, the presence of Atmosphere 2020, 11, 1324; doi:10.3390/atmos11121324 www.mdpi.com/journal/atmosphere
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