[Chemical Constituents and Sources of PM2.5 Around the Wuhan Military Games Period].

Hourly monitoring datasets of PM2.5 mass concentration and associated chemical compositions were used to investigate the variations in their mass concentrations before, during, and after the 7th Military World Games held in Wuhan. Furthermore, the source analysis was conducted through PMF combined with the backward trajectory and concentration weighted trajectory cluster analysis. The study revealed the variations in PM2.5 compositions and sources around the Wuhan Military Games period and their response to local and surrounding regional control measures. This can provide a reference for regional precise prevention and control of PM2.5. Under the influence of emission reduction measures, PM2.5 mass concentration during the control period [(31.3±12.0) µg·m-3] decreased by 14.7% compared with that before the control period, whereas the secondary components were obviously formed, in which sulfate, nitrate, and ammonium(SNA) increased by 25.6% in total. After the control period, owing to the decrease in humidity and the influence of the northwest air mass, the mass concentration of SNA decreased by 36.9%, whereas the mass concentration of mineral elements increased by 4.7 times. The source apportionment results indicated that there was no significant difference between the vehicle emissions before and after the control(P<0.05). Compared with that in the non-control period, the contributions of industrial emission and coal burning decreased by 68.1% and 43.7%, respectively, whereas the contribution of secondary inorganic aerosol increased by 89.5%. With the lack of large-scale control of vehicle emissions, the mass concentrations of NO3- and NOx increased by 6.13 µg·m-3 and 3.56 µg·m-3, respectively. The vehicle emissions peaked at 21:00 [(10.9±3.67) µg·m-3], reflecting the emissions of cargo vehicles, which were only allowed to pass at night during the control period. With the banning of ship navigation, the ship emission in the middle and lower reaches of the Yangtze River significantly decreased(48.8%). There were also high values of fugitive dust and industrial emissions near the Anhui section of the Yangtze River waterway, which reflected the dense distribution of industrial activities and road transportation along the Yangtze River. After the control period, the fugitive dust increased by 6.6 times, and the source areas were mainly distributed in Xiangyang and Jingmen.

Response of PM2.5 pollution to meteorological and anthropogenic emissions changes during COVID-19 lockdown in Hunan Province based on WRF-Chem model.

In December 2019, the New Crown Pneumonia (the COVID-19) outbroke around the globe, and China imposed a nationwide lockdown starting as early as January 23, 2020. This decision has significantly impacted China's air quality, especially the sharp decrease in PM2.5 (aerodynamic equivalent diameter of particulate matter less than or equal to 2.5 µm) pollution. Hunan Province is located in the central and eastern part of China, with a "horseshoe basin" topography. The reduction rate of PM2.5 concentrations in Hunan province during the COVID-19 (24.8%) was significantly higher than the national average (20.3%). Through the analysis of the changing character and pollution sources of haze pollution events in Hunan Province, more scientific countermeasures can be provided for the government. We use the Weather Research and Forecasting with Chemistry (WRF-Chem, V4.0) model to predict and simulate the PM2.5 concentrations under seven scenarios before the lockdown (2020.1.1-2020.1.22) and during the lockdown (2020.1.23-2020.2.14). Then, the PM2.5 concentrations under different conditions is compared to differentiate the contribution of meteorological conditions and local human activities to PM2.5 pollution. The results indicate the most important cause of PM2.5 pollution reduction is anthropogenic emissions from the residential sector, followed by the industrial sector, while the influence of meteorological factors contribute only 0.5% to PM2.5. The explanation is that emission reductions from the residential sector contribute the most to the reduction of seven primary contaminants. Finally, we trace the source and transport path of the air mass in Hunan Province through the Concentration Weight Trajectory Analysis (CWT). We found that the external input of PM2.5 in Hunan Province is mainly from the air mass transported from the northeast, accounting for 28.6%-30.0%. To improve future air quality, there is an urgent need to burn clean energy, improve the industrial structure, rationalize energy use, and strengthen cross-regional air pollution synergy control.

Exploring the driving factors of haze events in Beijing during Chinese New Year holidays in 2020 and 2021 under the influence of COVID-19 pandemic.

Unexpected outbreak of the 2019 novel coronavirus (COVID-19) has profoundly altered the way of human life and production activity, which posed visible impacts on PM2.5 and its chemical species. The abruptly emergency reduction in human activities provided an opportunity to explore the synergetic impacts of multi-factors on shaping PM2.5 pollution. Here, we conducted two comprehensive observation measurements of PM2.5 and its chemical species from 1 January to 16 February in Beijing 2020 and the same lunar date in 2021, to investigate temporal variations and reveal the driving factors of haze before and after Chinese New Year (CNY). Results show that mean PM2.5 concentrations during the whole observation were 63.83 and 66.86 µg/m3 in 2020 and 2021, respectively. Higher secondary inorganic species were observed after CNY, and K+, Cl- showed three prominent peaks which associated closely with fireworks burnings from suburb Beijing and surroundings, verifying that they could be used as two representative tracers of fireworks. Further, we explored the impacts of meteorological conditions, regional transportation as well as chemical reactions on PM2.5. We found that unfavorable meteorological conditions accounted for 11.0 % and 16.9 % of PM2.5 during CNY holidays in 2020 and 2021, respectively. Regional transport from southwest and southeast (south) played an important role on PM2.5 during the two observation periods. Higher ratio of NO3-/SO42- were observed under high OX and low RH conditions, suggesting the major pathway of NO3- and SO42- formation could be photochemical process and aqueous-phase reaction. Additionally, nocturnal chemistry facilitated the formation of secondary components of both inorganic and organic. This study promotes understandings of PM2.5 pollution in winter under the influence of COVID-19 pandemic and provides a well reference for haze and PM2.5 control in future.

Ambient particle characteristics by single particle aerosol mass spectrometry at a coastal site in Hong Kong: a case study affected by the sea-land breeze.

The sea-land breeze (SLB) circulation plays a vital role in the transport of atmospheric pollutants in coastal cities. In this study, a single particle aerosol mass spectrometer (SPAMS) and combined bulk aerosol instruments were deployed to investigate the ambient particle characteristic at a suburban coastal site in Hong Kong from February 22 to March 10, 2013. Significant SLB circulations were captured from March 6-10, 2013, during the campaign. During the SLB periods, air quality worsened, with PM2.5 concentrations reaching a peak of 55.6 µg m-3 and an average value of 42.8 ± 4.5 µg m-3. A total of 235,894 particles were measured during the SLB stage. Eight major sources were identified by investigating the mixing states of the total particles, including the coal-burning related particles (48.1%), biomass burning particles (6.7%), vehicle emission-related particles (16.4%), sea salt (9.2%), ship emission particles (2.7%), dust/steeling industries (3.7%), waste incineration (6.3%), and road dust (3.9%). It was noteworthy that the PM2.5 concentrations and particle numbers increased sharply during the transition of land wind to the sea breeze. Meanwhile, the continental sourced pollutants recirculated back to land resulting in a cumulative increase in pollutants. Both individual and bulk measurements support the above results, with high contributions from coal burning, biomass burning, bulk K+, and NO3 -, which were probably from the regional transportation from the nearby area. In contrast, the ship and vehicle emissions increased during the SLB period, with a high sulfate concentration partially originating from the ship emission. In this study, field evidence of continental-source pollutants backflow to land with the evolution of sea breeze was observed and helped our current understanding of the effect of SLB on air quality in the coastal city.

[Real-time Source Apportionment of PM2.5 and Potential Geographic Origins of Each Source During Winter in Wuhan].

China has always suffered from serious atmospheric fine particle (PM2.5) pollution in winter, and PM2.5 in Wuhan is particularly affected by regional transportation. Based on the hourly monitoring dataset of chemical components during the winter period, this study identified the real-time sources of PM2.5 in Wuhan using a positive matrix factorization (PMF) model. A cluster analysis of backward trajectories and the concentration weighted trajectory were applied to obtain the potential source regions and transportation routes. During the observation period, ρ(PM2.5) was (75.1±29.2) µg·m-3, and there were two pollution episodes, one of which was mainly affected by the air masses coming from the northwest direction. In the first pollution episode, the increasing concentration of water-soluble ions was the main reason for the high PM2.5 value, and the concentrations of NH4+, NO3-, and SO42- were 1.6, 1.7, and 2.1 times those during the cleaning period, respectively. The other episode was affected by the air masses coming from the east direction, and the secondary organic components were clearly formed. Secondary inorganic aerosol contributed the most (34.1%) to PM2.5, followed by vehicular exhaust (23.7%), coal combustion (11.5%), road dust (10.9%), iron- and steel-producing processes (8.7%), and firework displays (5.7%). Biomass burning contributed the least (5.3%). Our examination of the diurnal variation revealed that the maximum contribution of iron- and steel-producing processes appeared at 08:00[(17.5±18.8) µg·m-3], and the lowest was at 01:00[(10.4±10.9) µg·m-3], which stayed high in the daytime and low at night. The contribution of vehicular exhaust showed a double peak at 09:00[(42.1±24.8) µg·m-3] and 20:00[(41.6±19.5) µg·m-3]. In the first pollution period, the contribution rate of secondary inorganic aerosol increased significantly, indicating that the long-distance transport under the northwest air mass promoted the generation of secondary components. In the second pollution period, the contribution rates of vehicular exhaust, coal combustion, iron- and steel-producing processes, and road dust increased, mainly located in the local area, the northwest of Jiangxi and the south of Anhui province. This reflected the influence of industrial processes, road transportation, and dust contribution along the Yangtze River on PM2.5. Biomass burning had a relatively high contribution for air masses from the northern regions, including Henan, Anhui, the south of Hebei, and the southwest of Shanxi provinces. The regional transport of pollutants from biomass combustion in the North China Plain during the winter would have an impact on Wuhan. This study can provide scientific and technological support for identifying the causes of atmospheric haze pollution in Wuhan during the winter and for the joint prevention and control of atmospheric particulate matter.

Substantial changes of chemical composition and sources of fine particles during the period of COVID-19 pandemic in Taiyuan, Northern China.

To better understand the effects of COVID-19 on air quality in Taiyuan, hourly in situ measurements of PM2.5(particulate matter with an aerodynamic diameter less than 2.5 mm) and chemical components (water-soluble ions, organic carbon (OC), elemental carbon (EC), and trace elements) were conducted before (P1: 1 January-23 January 2020) and during (P2: 24 January-15 February 2020) the coronavirus disease 2019 (COVID-19) outbreak. The average concentrations of PM2.5 dropped from 122.0 µg/m3 during P1 to 83.3 µg/m3 during P2. Compared with P1, except for fireworks burning-related chemical components (K+, Mg2+, K, Cu, Ba), the concentrations of other chemical components of PM2.5 decreased by14.9-69.8%. Although the large decrease of some emission sources, fireworks burning still resulted in the occurrence of pollution events during P2. The analysis results of positive matrix factorization model suggested that six PM2.5 sources changed significantly before and during the outbreak of the epidemic. The contributions of vehicle emission, industrial process, and dust to PM2.5 decreased from 23.1%, 3.5%, and 4.0% during P1 to 7.7%, 3.4%, and 2.3% during P2, respectively, whereas the contributions of secondary inorganic aerosol, fireworks burning, and coal combustion to PM2.5 increased from 62.0%, 1.8%, and 5.5% to 71.5%, 9.0%, and 6.2%, respectively. The source apportionment results were also affected by air mass transport. The largest reductions of vehicle emission, industrial process, and dust source were distinctly seen for the air masses from northwest. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11869-021-01082-y.

Significant changes in the chemical compositions and sources of PM2.5 in Wuhan since the city lockdown as COVID-19.

Wuhan was the first city to adopt the lockdown measures to prevent COVID-19 spreading, which improved the air quality accordingly. This study investigated the variations in chemical compositions, source contributions, and regional transport of fine particles (PM2.5) during January 23-February 22 of 2020, compared with the same period in 2019. The average mass concentration of PM2.5 decreased from 72.9 µg m-3 (2019) to 45.9 µg m-3 (2020), by 27.0 µg m-3. It was predominantly contributed by the emission reduction (92.0%), retrieved from a random forest tree approach. The main chemical species of PM2.5 all decreased with the reductions ranging from 0.85 µg m-3 (chloride) to 9.86 µg m-3 (nitrate) (p < 0.01). Positive matrix factorization model indicated that the mass contributions of seven PM2.5 sources all decreased. However, their contribution percentages varied from -11.0% (industrial processes) to 8.70% (secondary inorganic aerosol). Source contributions of PM2.5 transported from potential geographical regions showed reductions with mean values ranging from 0.22 to 4.36 µg m-3. However, increased contributions of firework burning, secondary inorganic aerosol, road dust, and vehicle emissions from transboundary transport were observed. This study highlighted the complex and nonlinear response of chemical compositions and sources of PM2.5 to air pollution control measures, suggesting the importance of regional-joint control.

Synoptic pattern and planetary boundary layer structure associated with aerosol pollution during winter in Beijing, China.

The day-to-day variations in the planetary boundary layer (PBL) structure and air quality are closely governed by large-scale synoptic forcings. Partly due to the lack of long-term PBL observations during the winter in Beijing, the complex relationships between the large-scale synoptic patterns, local PBL structures/processes, and PM2.5 pollution have not been fully understood. Thus, this study systematically investigated these linkages by combining aerosol measurements, surface meteorological observations, radiosonde data, reanalysis, long-term three-dimensional meteorological simulations, and idealized meteorology-chemistry coupled simulations. Based on the validated long-term simulation results, the boundary layer height (BLH) in Beijing during two winters from 2013 to 2015 was calculated and compared with PM2.5 measurements. A significant anti-correlation was found between the daily BLH and PM2.5 concentration in Beijing, indicating the importance of the PBL structure on the variations in the aerosol pollution levels. Those days with low BLHs are often accompanied by a strong elevated thermal inversion layer. Based on the daily 900-hPa geopotential height fields, seven synoptic patterns were identified using an objective approach, in which two types were found to be associated with heavy PM2.5 pollution in Beijing. One pattern was characterized by weak northwesterly prevailing winds and a strong elevated thermal inversion layer over Beijing, and the local emissions of aerosols played a decisive role in the formation of heavy pollution. The other pattern was associated with southerly prevailing winds, which could transport the pollutants emitted from southern cities to Beijing. According to the meteorology-chemistry coupled simulations, southerly regional transportation can contribute approximately 56% of the PM2.5 in Beijing. The results of this study have important implications for understanding the crucial roles that multiscale meteorological factors play in modulating the aerosol pollution in Beijing during the winter.

Case study of spring haze in Beijing: Characteristics, formation processes, secondary transition, and regional transportation.

Continuous haze monitoring was conducted from 12:00 3 April to 12:00 8 April 2016 in Beijing, China to develop a more detailed understanding of spring haze characteristics. The PM2.5 concentration ranged from 6.30 to 165 µg m-3 with an average of 63.8 µg m-3. Nitrate was the most abundant species, accounting for 36.4% of PM2.5, followed by organic carbon (21.5%), NH4+ (19.3%), SO42- (18.8%), and elemental carbon (4.10%), indicating the key role of nitrate in this haze event. Species contribution varied based on the phase of the haze event. For example, sulfate concentration was high during the haze formation phase, nitrate was high during the haze, and secondary organic carbon (SOC) had the highest contribution during the scavenging phase. The secondary transition of sulfate was influenced by SO2, followed by relative humidity (RH) and Ox (O3+NO2). Nitrate formation occurred in two stages: through NO2 oxidation, which was vulnerable to Ox; and by the partitioning of N (+5) which was susceptible to RH and temperature. SOC tended to form when Ox and RH were balanced. According to hourly species behavior, sulfate and nitrate were enriched during haze formation when the mixed layer height decreased. However, SOC accumulated prior to the haze event and during formation, which demonstrated the strong contribution of secondary inorganic aerosols, and the limiting contribution of SOC to this haze case. Investigating backward trajectories showed that high speed northwestern air masses following a straight path corresponded to the clear periods, while southwesterly air masses which traversed heavily polluted regions brought abundant pollutants to Beijing and stimulated the occurrence of haze pollution. Results indicate that the control of NO2 needs to be addressed to reduce spring haze. Finally, the correlation between air mass trajectories and pollution conditions in Beijing reinforce the necessity of inter-regional cooperation and control.

[Capacity Simulation Method Based on Regional Transfer Matrix and PM2.5 Concentration Target Constraint].

Atmospheric environmental capacity is an important reference in environmental planning. To meet the PM2.5 standard, a new method is proposed to balance the capacity among cities of Guangdong, with screening of the most unfavorable meteorological year and combining it with the regional transportation calculated by the CAMx-PSAT module. Pollutant overloading and capacity scenarios were also calculated. The results showed that, under the constraints of the cities' annual PM2.5 ≤ 35 µg·m-3, the capacities of SO2, NOx, NH3, and PM2.5 in Guangdong were about 6.8×105 tons, 1.35×106 tons, 4.6×105 tons, and 5.1×105 tons, respectively. Based on the benchmark scenario, SO2 emissions in Guangdong were overloaded by 10%, and the emissions of NOx, NH3, and PM2.5 exceeded by 12%, 9%, and 20%, respectively, compared to those of the capacity scenario. Ranked by the number of overloaded species in Guangdong, the cities of Guangzhou, Foshan, Zhongshan, and Qingyuan were on top. When achieving the capacity scenario, the annual PM2.5 concentration in Guangdong was about 30 µg·m-3, which meets the national secondary ambient air quality standard.