In January 2013, a long-lasting episode of severe haze occurred in central and eastern China, and it attracted attention from all sectors of society. The process and evolution of haze pollution ...episodes were observed by the ＂Forming Mechanism and Con- trol Strategies of Haze in China＂ group using an intensive aerosol and trace gases campaign that simultaneously obtained data at 11 ground-based observing sites in the CARE-China network. The characteristics and formation mechanism of haze pollu- tion episodes were discussed. Five haze pollution episodes were identified in the Beijing-Tianjin-Hebei （Jing-Jin-Ji） area; the two most severe episodes occurred during 9-15 January and 25-31 January. During these two haze pollution episodes, the maximum hourly PMz5 mass concentrations in Beijing were 680 and 530 ~tg m-3, respectively. The process and evolution of haze pollution episodes in other major cities in the Jing-Jin-Ji area, such as Shijiazhuang and Tianjin were almost the same as those observed in Beijing. The external cause of the severe haze episodes was the unusual atmospheric circulation, the depres- sion of strong cold air activities and the very unfavorable dispersion due to geographical and meteorological conditions. How- ever, the internal cause was the quick secondary transformation of primary gaseous pollutants to secondary aerosols, which contributed to the ＂explosive growth＂ and ＂sustained growth＂ of PM2.5. Particularly, the abnormally high amount of nitric ox- ide （NOx） in the haze episodes, produced by fossil fuel combustion and vehicle emissions, played a direct or indirect role in the quick secondary transformation of coal-burning sulphur dioxide （SO2） to sulphate aerosols. Furthermore, gaseous pollutants were transformed into secondary aerosols through heterogeneous reactions on the surface of fine particles, which can change the particle＇s size and chemical composition. Consequently, the proportion of secondary inorganic ions, such as sulphate and nitrate, gradually increased, which enhances particle hygroscopicity and thereby accelerating formation of the haze pollution.
•Anthropogenic species substantially accumulated in both fine and coarse particles.•Secondary organic carbon in PM1.1 decreased from clear to haze days.•The mass peak shifted to larger particles from ...clear to haze days.•The NO3−/SO42− ratio decreased with enhanced haze pollution.•Both mobile local and stationary regional sources were vital for haze formation.
Using size-resolved filter sampling and chemical characterization, high concentrations of water-soluble ions, carbonaceous species and heavy metals were found in both fine (PM2.1) and coarse (PM2.1–9) particles in Beijing during haze events in early 2013. Even on clear days, average mass concentration of submicron particles (PM1.1) was several times higher than that previously measured in most of abroad urban areas. A high concentration of particulate matter on haze days weakens the incident solar radiation, which reduces the generation rate of secondary organic carbon in PM1.1. We show that the peak mass concentration of particles shifted from 0.43–0.65μm on clear days to 0.65–1.1μm on lightly polluted days and to 1.1–2.1μm on heavily polluted days. The peak shifts were also found for the following species: organic carbon, elemental carbon, NH4+, SO42−, NO3−, K, Cu, Zn, Cd and Pb. Our findings demonstrate that secondary inorganic aerosols (36%) and organic matter (26%) dominated the fine particle mass on heavily polluted days, while their contribution reduced to 29% and 18%, respectively, on clear days. Besides fine particles, anthropogenic chemical species also substantially accumulated in the coarse mode, which suggests that particles with aerodynamic diameter larger than 2.1μm cannot be neglected during severe haze events.
PM2.5-bound polycyclic aromatic hydrocarbons (PAHs) during winter 2015 at three urban sites, including Beijing, Tianjin and Shijiazhuang, and one background site (Xinglong) over the North China Plain ...(NCP) were investigated. The spatial variations of PAHs showed the same trends with PM2.5 mass concentrations, i.e. the highest PAHs concentrations was in Shijiazhuang, followed by Tianjin, Beijing and the lowest PAHs concentrations was in Xinglong. The diurnal variations of PAHs exhibited PAHs concentrations during nighttime were higher than those during daytime. The dominant species in PAHs were fluranthene and benzob + kfluoranthene, indicating that diesel vehicle emission, coal combustion and biomass burning could be important and potential sources for PAHs over the NCP. There results were supported by diagnostic ratios analysis. But coefficient of divergence analysis showed that a high extent of spatial contrast among four sampling sites, except between Beijing and Tianjin. Analysis of toxicity equivalent quantities (TEQ) and the lifetime excess cancer risk (ECR) from inhalation exposure to PAHs showed that 818, 1517, 5129 and 182 cases per 100,000 people exposed in Beijing, Tianjin, Shijiazhuang and Xinglong, respectively, which were much higher than the threshold value suggested by US-EPA, i.e. 1 case per 100,000 people, and indicating that the NCP suffered from very serious health risk from PAHs, especially in Shijiazhuang.
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•PAHs had higher mass concentrations at urban sites than those at background site.•BaP concentrations at three urban sites were much higher than WHO and NAAQ standards.•Fossil fuel combustion, biomass and coal combustion were the main sources of PAHs over the NCP.•Toxicity equivalent quantities based on PAHs revealed a high health risk to residents over the NCP.
Particulate matter (PM) pollution is a serious issue that has aroused great public attention in Beijing. To examine the seasonal characteristics of aerosols in typical pollution episodes, ...water-soluble inorganic ions (SO42−, NO3−, NH4+, Cl−, K+, Na+, Ca2+ and Mg2+) in size-segregated PM collected by an Anderson sampler (equipped with 50% effective cut-off diameters of 9.0, 5.8, 4.7, 3.3, 2.1, 1.1, 0.65, 0.43μm and an after filter) were investigated in four intensive campaigns from June 2013 to May 2014 in the Beijing urban area. Pronounced seasonal variation of TWSIs in fine particles (aerodynamic diameter less than 2.1μm) was observed, with the highest concentration in summer (71.5±36.3μg/m3) and the lowest in spring (28.1±15.2μg/m3). Different ion species presented different seasonal characteristics of mass concentration and size distribution, reflecting their different dominant sources. As the dominant component, SO42−, NO3− and NH4+ (SNA) in fine particles appeared to play an important role in the formation of high PM pollution since its contribution to the TWSIs and PM2.1 mass increased significantly during pollution episodes. Due to the hygroscopic growth and enhanced secondary formation in the droplet mode (0.65–2.1μm) from clean days to polluted days, the size distribution peak of SNA in the fine mode tended to shift from 0.43–0.65μm to 0.65–2.1μm. Relative humidity (RH) and temperature contributed to influence the secondary formation and regulate the size distributions of sulfates and nitrates. Partial correlation analysis found that high RH would promote the sulfur and nitrogen oxidation rates in the fine mode, while high temperature favored the sulfur oxidation rate in the condensation mode (0.43–0.65μm) and reduced the nitrogen oxidation rate in the droplet mode (0.65–2.1μm). The NO3−/SO42− mass ratio in PM2.1 (73% of the samples) exceeded 1.0, suggesting that vehicle exhaust currently makes a greater contribution to aerosol pollution than stationary sources in Beijing.
•Seasonal characteristics of size-segregated ions in pollution episodes were analyzed.•Contribution of droplet-mode secondary ions was clearly elevated on polluted days.•Relative humidity and temperature affect secondary formation of sulfate and nitrate.
Accurate determination of the atmospheric particulate matter mass concentration and chemical composition is helpful in exploring the causes and sources of atmospheric enthalpy pollution and in ...evaluating the rationality of environmental air quality control strategies. Based on the sampling and chemical composition data of PM
2.5
in different key regions of China in the CARE-China observation network, this research analyzes the environmental air quality data released by the China National Environmental Monitoring Centre during the studied period to determine the changes in the particulate matter mass concentration in key regions and the evolution of the corresponding chemical compositions during the implementation of the
Action Plan for Prevention and Control of Air Pollution
from 2013–2017. The results show the following. (1) The particulate matter mass concentration in China showed a significant downward trend; however, the PM
2.5
annual mass concentration in 64% of cities exceeds the New Chinese Ambient Air Quality Standard (CAAQS) Grade II (GB3095-2012). The region to the east of the Taihang Mountains, the Fenhe and Weihe River Plain and the Urumqi-Changji regions in Xinjiang, all have PM
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concentration loading that is still high, and heavy haze pollution occurred frequently in the autumn and winter. (2) During the heavy pollution in the autumn and winter, the concentrations of sulfate and organic components decreased significantly. The mean
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concentration in PM
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decreased by 76%, 12%, 81% and 38% in Beijing-Tianjin-Hebei (BTH), the Pearl River Delta (PRD), the Sichuan-Chongqing region (SC) and the Fenhe and Weihe River Plain, respectively. The mean organic matter (OM) concentration decreased by 70%, 44%, 48% and 31%, respectively, and the mean concentration of
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decreased by 68%, 1.6%, 38% and 25%, respectively. The mean elemental carbon (EC) concentration decreased by 84% and 20% in BTH and SC, respectively, and it increased by 61% and 11% in the PRD and Fenhe and Weihe River Plain, respectively. The mean concentration of mineral and unresolved chemical components (MI) dropped by 70%, 24% and 13% in BTH, the PRD and the Fenhe and Weihe River Plain, respectively. The change in the PM
2.5
chemical composition is consistent with the decrease of the PM
2.5
mass concentration. (3) In 2015, the mean OM concentration contributions to fine particles and coarse particles were 13–46% and 46–57%, respectively, and the mean MI concentration contributions to fine particles and coarse and particles were 31–60% and 39–73%, respectively; these values are lower than the 2013 values from the key regions, which is the most important factor behind the decrease of the particulate matter mass concentration. From 2013 to 2015, among the chemical components of different particle size fractions, the peak value of the coarse particle size fraction decreased significantly, and the fine particle size fractions of
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−
,
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,
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n
d
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decreased with the decrease of the particulate matter mass concentration in different particle size fractions. The fine-particle size peaks of
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−
,
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,
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shifted from 0.65–1.1 μm to the finer size range of 0.43–0.65 μm during the same time frame.
Size-segregated water-soluble ionic species (WSIs) were measured using an Anderson cascade impactor from Jul. to Aug. 2008 and from Dec. 2009 to Feb. 2010 in urban Beijing. The results showed that ...fine particles (PM2.1, Dp < 2.1 μm) accounted for ∼49% (summer) and ∼34% (winter) of the total particulate mass, and WSIs accounted for 23–82% of the mass concentration of PM2.1. Secondary inorganic aerosols (SIAs, the sum of SO42−, NO3− and NH4+) accounted for more than 30% of the fine particles, which were greatly elevated during particle pollution events (PM events), thereby leading to an alteration of the size distributions of SO42− and NO3− to nearly single fine-mode distributions peaking at 0.65–2.1 μm. This finding suggests that heterogeneous aqueous reactions were enhanced at high RH values. SIAs also increased during dust events, particularly for coarse mode SO42−, which indicated enhanced heterogeneous reactions on the dust surface. The positive matrix factorization (PMF) model was used to resolve the bulk mass size distributions into condensation, droplet, and coarse modes, representing the three major sources of the particles. The formation of SO42− was attributed primarily to in-cloud or aerosol droplet processes during summer (45%), and the heterogeneous reaction of SO2 on mineral dust surfaces was an important formation pathway during winter (45%). The formation pathways of NO3− in fine particles were similar to those of SO42−, where over 30% were formed by in-cloud processes. This work provides important field measurement-based evidence for understanding the formation pathway of secondary inorganic aerosols in the megacity of Beijing.
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•SIA in the range of 0.65–2.1 μm exhibited the most dramatic increase in PM events.•Dust particles enhance sulfate and nitrate concentration in fine and coarse particles.•The formation of SIA in fine particles was mainly attributed to in-cloud process.•The coarse mode nitrate formation was different from sulfate.
Organic carbon (OC) and elemental carbon (EC) in PM2.5 were measured hourly with a semicontinuous thermal-optical analyzer in urban Beijing, China, from Mar 1, 2013 to Feb 28, 2014. The annual mean ...concentrations of OC and EC in Beijing were 14.0 ± 11.7 and 4.1 ± 3.2 μg/m3, respectively. The concentrations observed in this study were lower than those of other reports over the past ten years; however, the concentrations were higher than those reported from most of the megacities in North America and Europe. These findings suggest that OC and EC remained at high levels despite the implementation of strict control measures to improve air quality. The OC and EC concentrations exhibited strong seasonality, with high values in the autumn and winter but low values in the spring and summer in Beijing. The diurnal OC and EC cycles were characterized by higher values at night and in the morning because of primary emissions, accumulations and low boundary-layer heights. Due to increasing photochemical activity, a well-defined OC peak was observed at approximately noon. The OC and EC concentrations followed typical lognormal patterns in which more than 75% of the OC samples had concentrations between 0.9 and 18.0 μg/m3 and 75% of the EC samples had concentrations between 0.4 and 5.6 μg/m3. An EC tracer method and combined EC tracer and K+ mass balance methods were used to estimate the contributions from secondary formation and biomass burning, respectively. High secondary organic carbon (SOC) concentrations were found in the autumn and winter due to low temperatures, which are favorable for the absorption and condensation of semi-volatile organic compounds on existing particles. High correlations were found between the estimated SOC in PM2.5 and the observed OOA (oxidized organic aerosol) in PM1; thus, the method proved to be effective and reliable. The annual average OCBiomass burning (OCbb) contribution to the total OC concentration was 18.4%, suggesting that biomass burning is a substantial pollution factor in Beijing.
•Semi-continuous measurements of carbonaceous aerosols were obtained in Beijing.•Seasonal, weekly and diurnal variations of OC and EC are reported.•Clean energy strategies resulted in an effective reduction of OC and EC.•High SOC concentrations were observed in autumn and winter.•Biomass burning emissions accounted for 18.4% of OC.
Haze is a serious air pollution problem in China, especially in Beijing and surrounding areas, affecting visibility, public health and regional climate. In this study, the Weather Research and ...Forecasting-Chemistry (WRF-Chem) model was used to simulate PM2.5 (particulate matters with aerodynamic diameter ≤2.5μm) concentrations during the 2013 severe haze event in Beijing, and health impacts and health-related economic losses were calculated based on model results. Compared with surface monitoring data, the model results reflected pollution concentrations accurately (correlation coefficients between simulated and measured PM2.5 were 0.7, 0.4, 0.5 and 0.6 in Beijing, Tianjin, Xianghe and Xinglong stations, respectively). Health impacts assessments show that the PM2.5 concentrations in January might cause 690 (95% confidence interval (CI): (490, 890)) premature deaths, 45,350 (95% CI: (21,640, 57,860)) acute bronchitis and 23,720 (95% CI: (17,090, 29,710)) asthma cases in Beijing area. Results of the economic losses assessments suggest that the haze in January 2013 might lead to 253.8 (95% CI: (170.2, 331.2)) million US$ losses, accounting for 0.08% (95% CI: (0.05%, 0.1%)) of the total 2013 annual gross domestic product (GDP) of Beijing.
•Health impacts of the 2013 Beijing haze event are estimated.•Health-related economic losses are also calculated.•The PM2.5 concentrations in January 2013 might cause 690 deaths.•This haze event might lead to 253.8 million US$ losses.
North China registers frequent air pollution episodes from high PM2.5 concentrations. Shijiazhuang is located at the intensive industrial zone of this region, but there is insufficient data on the ...chemical composition of PM2.5 and its sources in this city. In this study, the chemical and seasonal characteristics of PM2.5 in Shijiazhuang were investigated based on 12-h integrated PM2.5 measurements made over eight 1-month periods in each season between June 2014 and April 2016 (486 samples). The eight-season average concentration of PM2.5 was 138.8 μg m−3, and the major chemical components were secondary inorganic aerosol (SIA) species of sulfate, nitrate, and ammonium (41.5%), followed by organic matter (25.9%). The mass concentration and most of the chemical components of PM2.5 showed clear seasonal variation, with a winter-high and summer-low pattern. SO42− and NO3− were the dominant components at each pollution level in summer and autumn (18.1%–30.6% and 14.2%–27.0%, respectively). Sufficient gaseous oxidants (O3) concentrations and suitable meteorology conditions were observed in these two seasons. Highest SOR (0.61), SO42−/EC(10.8) and NOR (0.58), NO3−/EC (5.9) were found in summer and autumn, which indicated intense secondary transformation in these two seasons. Organic matter was the dominant species in winter, which increased from 17.1 μg m−3 for clean days (28.7% of PM2.5) to 169.1 μg m−3 (38.4% of PM2.5). The accumulation of primary emissions (coal combustion and biomass burning) was responsible for the increasing OM trend (especially for POC). The highest and leading proportion of mineral dust occurred in spring (20.3%–46.5%) as a result of higher wind speeds (up to 3 m/s). Potential source contribution function (PSCF) analyses implied that the border areas of Hebei, Henan and Shandong Provinces, together with the central area of Shanxi Province, contributed significantly to the PM2.5 pollution in Shijiazhuang, especially in autumn and winter.
Major components (SO42−, NO3−, primary organic carbon (POC), secondary organic carbon (SOC) and mineral dusts) of PM2.5, SOR and NOR at different pollution level of each season.
C: Clean days; SL: Slightly polluted days; MP: Moderately polluted days; HP: Heavily polluted days; SEP: Severely polluted days. Display omitted
•SIA and OM were the major components of PM2.5 in Shijiazhuang.•High atmospheric oxidation was conducive to form SIA in summer and autumn.•Biomass burning and coal combustion contributed to the high OM in autumn and winter.•Regional transportation contributed significantly to the PM2.5 pollution in Shijiazhuang.
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