Seasonal variations and chemical characteristics of PM(2.5) in Wuhan, central China

An Integrated Method for Factor Number Selection of PMF Model: Case Study on Source Apportionment of Ambient Volatile Organic Compounds in Wuhan

The positive matrix factorization (PMF) model is widely used for source apportionment of volatile organic compounds (VOCs). The question about how to select the proper number of factors, however, is rarely studied. In this study, an integrated method to determine the most appropriate number of sources was developed and its application was demonstrated by case study in Wuhan. The concentrations of 103 ambient volatile organic compounds (VOCs) were measured intensively using online gas chromatography/mass spectrometry (GC/MS) during spring 2014 in an urban residential area of Wuhan, China. During the measurement period, the average temperature was approximately 25 °C with very little domestic heating and cooling. The concentrations of the most abundant VOCs (ethane, ethylene, propane, acetylene, n-butane, benzene, and toluene) in Wuhan were comparable to other studies in urban areas in China and other countries. The newly developed integrated method to determine the most appropriate number of sources is in combination of a fixed minimum threshold value for the correlation coefficient, the average weighted correlation coefficient of each species, and the normalized minimum error. Seven sources were identified by using the integrated method, and they were vehicular emissions (45.4%), industrial emissions (22.5%), combustion of coal (14.7%), liquefied petroleum gas (LPG) (9.7%), industrial solvents (4.4%), and pesticides (3.3%) and refrigerants. The orientations of emission sources have been characterized taking into account the frequency of wind directions and contributions of sources in each wind direction for the measurement period. It has been concluded that the vehicle exhaust contribution is greater than 40% distributed in all directions, whereas industrial emissions are mainly attributed to the west southwest and south southwest.

Particulate Matter and Gaseous Pollutions in Three Metropolises along the Chinese Yangtze River: Situation and Implications

The situation of criteria atmospheric pollutants, including particulate matter and trace gases (SO₂, NO₂, CO and O₃), over three metropolises (Chongqing, Wuhan, and Nanjing), representing the upstream, midstream and downstream portions of the Yangtze River Basin from September 2015 to August 2016 were analyzed. The maximum annual mean PM2.5 and PM10 concentrations were 61.3 and 102.7 μg/m³ in Wuhan, while highest annual average gaseous pollutions occurred in Nanjing, with 49.6 and 22.9 ppb for 8 h O₃ and NO₂, respectively. Compared to a few years ago, SO₂ and CO mass concentrations have dropped to well below the qualification standards, and the O₃ and NO₂ concentrations basically meet the requirements though occasionally is still high. In contrary, about 13%, 25%, 22% for PM2.5, and 4%, 17%, 15% for PM10 exceed the Chinese Ambient Air Quality Standard (CAAQS) Grade II. Particulate matter, especially PM2.5, is the most frequent major pollutant to poor air quality with 73%, 64% and 88% accounting for substandard days. Mean PM2.5 concentrations on PM2.5 episode days are 2⁻3 times greater than non-episode days. On the basis of calculation of PM2.5/PM10 and PM2.5/CO ratios, the enhanced particulate matter pollution on episode days is closely related to secondary aerosol production. Except for O₃, the remaining five pollutants exhibit analogous seasonal patterns, with the highest magnitude in winter and lowest in summer. The results of back trajectories show that air pollution displays synergistic effects on local emissions and long range transport. O₃ commonly demonstrated negative correlations with other pollutants, especially during winter, while moderate to strong positive correlation between particulate matter and NO₂, SO₂, CO were seen. Compared to pollutant substandard ratios over three megacities in eastern China (Beijing, Shanghai, and Guangzhou), the situation in our studied second-tier cities are also severe. The results in this paper provide basic knowledge for pollution status of three cities along Chinese Yangtze River and are conductive to mitigating future negative air quality levels.

Oxygen content determines the bio-reactivity and toxicity profiles of carbon black particles

In spite of the considerable efforts invested to understand the environmental health and safety (EHS) impacts of ultrafine particles, such as the representative PM2.5, there are still significant knowledge gaps to be filled. No conclusive understandings have been obtained about the physicochemical determinants in accounting for differential adverse outcomes. Here we compared the cytotoxicity of four carbon black (CB) particles with similar physicochemical properties except for their oxygen contents (C824455 < C1864 < Printex U < SB4A). We found that these four CB particles manifested in vitro and in vivo cytotoxicity reversely related to their oxygen contents, namely a hierarchy of cytotoxicity: C824455 > C1864 > Printex U > SB4A. Among these CB particles, the most significant lung injury (e.g. collapses and inflammation) and macrophagic activation were found for C824455 and C1864, in particular for C824455. All these differences in toxicity profiles, including in vitro and in vivo cytotoxicity, pro-inflammatory effects and direct damages to the lung epithelia, should be (at least partially) ascribed to the oxygen content in these CB particles that in turn determined their transformation, i.e. the different aggregation states. Nonetheless, PM2.5 likewise caused severe in vivo and in vitro toxicities to the lung cells and macrophages. This study thus offers more insights into the structure-activity relationship (SAR) and opens a new avenue to elucidate the physicochemical determinants in evoking lung injuries by ultrafine airborne particles.

Trace elements in PM2.5 in Shandong Province: Source identification and health risk assessment

The chemical compositions in PM_2.5 in metropolitan areas have obtained lots of attentions, of which concerns of airborne trace elements are relatively lacking. Here, PM_2.5 samples were collected simultaneously in one year at four urban sites (Zibo (ZB), Zaozhuang (ZZ), Qingdao (QD) and Jinan (JN (Shandong University)), and a rural site (JN (Miaopu)) in Shandong province. 25 elements (Al, Na, Cl, Mg, Si, S, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Sr, Cd, Ba and Pb) in PM_2.5 were measured by wavelength dispersive X-ray fluorescence spectrometer (WDXRF). Most trace elements (Al, Na, Cl, Mg, Si, Ca, Ti, Mn, Fe, Co, Ni, As, Se, Br, Cd, Ba and Pb) exhibited the highest levels at ZB and the lowest at QD. Meanwhile, they presented obvious seasonal variations with the highest concentrations in winter or spring and the lowest in summer. S and K were the most abundant elements in the area. In the non-crustal trace metal elements, Zn, Pb and Mn presented the highest concentrations. Positive matrix factorization (PMF) modeling revealed that secondary formation, coal combustion and industry emissions were the main sources in the region. The health risk assessments suggested that at the five sites Cd (diet) for adults, Pb and Co for children, and Mn (diet) for both adults and children (at ZB and SDU sites) had non-carcinogenic risks. As and Pb for adults and children existed carcinogenic risks, especially Pb for children. The sources of these elements with health risks were further explored. Notably, Cd, As and Pb should be paid special attention in the area due to their high concentrations in aerosol water exceeding the acceptable health risks, especially Pb.

Chemical characteristics and source apportionment of PM2.5 between heavily polluted days and other days in Zhengzhou, China

PM_2.5 samples were collected in Zhengzhou during 3years of observation, and chemical characteristics and source contribution were analyzed. Approximately 96% of the daily PM_2.5 concentrations and annual average values exceeded the Chinese National Ambient Air Quality Daily and Annual Standards, indicating serious PM_2.5 pollution. The average concentration of water-soluble inorganic ions was 2.4 times higher in heavily polluted days (daily PM_2.5 concentrations>250μg/m³ and visibility <3km) than that in other days, with sulfate, nitrate, and ammonium as major ions. According to the ratio of NO₃^-/SO₄^2-, stationary sources are still the dominant source of PM_2.5 and vehicle emission could not be ignored. The ratio of secondary organic carbon to organic carbon indicated that photochemical reactivity in heavily polluted days was more intense than in other days. Crustal elements were the most abundant elements, accounting for more than 60% of 23 elements. Chemical Mass Balance results indicated that the contributions of major sources (i.e., nitrate, sulfate, biomass, carbon and refractory material, coal combustion, soil dust, vehicle, and industry) of PM_2.5 were 13%, 16%, 12%, 2%, 14%, 8%, 7%, and 8% in heavily polluted days and 20%, 18%, 9%, 2%, 27%, 14%, 15%, and 9% in other days, respectively. Extensive combustion activities were the main sources of polycyclic aromatic hydrocarbons during the episode (Jan 1-9, 2015) and the total benzo[a]pyrene equivalency concentrations in heavily polluted days present significant health threat. Because of the effect of regional transport, the pollution level of PM_2.5 in the study area was aggravated.

A multicomponent kinetic model established for investigation on atmospheric new particle formation mechanism in H2SO4-HNO3-NH3-VOC system

Secondary new particle formation (NPF) plays a significant role in atmospheric particulate matters (e.g., PM2.5), and has been studied over the past decades. However, the mechanism of NPF still remains ambiguous, setting significant barrier for PM2.5 mitigations, especially in complex atmosphere with multi-pollutants. Since the NPF process can hardly be observed directly by experiment methods due to the measuring limitations, a multicomponent kinetic model (MKM), which can be used to analyze the process and the mechanism of NPF in H₂SO₄-HNO₃-NH₃-VOC (Volatile Organic Compounds) system, has been developed in this paper. According to MKM, seven cases with initial concentrations of total precursor vapors (CPV) in the range of 10⁷-10⁸cm^-3 were calculated to analyze the NPF process. Firstly, the 3nm particle (PM_3nm) formation rate was calculated via MKM, which showed a good agreement with the previous measurements. Moreover, according to MKM calculation, it is found that the peak value of PM_3nm formation rate, i.e., J_m, is proportional to [CPV]², while the time at which J_m occurred, i.e., t_m, is proportional to [CPV]^-1/3, indicating that the increases in CPV would lead to a significant increase of J_m and decrease of t_m. That's why NPF bursts immediately and PM2.5 pollution occurs suddenly in heavily pollutant areas. Afterwards, the roles of precursors in H₂SO₄-HNO₃-NH₃-VOC system were identified. It indicates that H₂SO₄, NH₃ and VOC mainly contribute to the early stage of the NPF, while the growth of the nuclei is mainly driven by HNO₃ and NH₃. And HNO₃ makes increasing contributions at the early stage of NPF with CPV rising (especially above 10⁸cm^-3). Thus in high CPV areas, especially for China, HNO₃ should be paid the same attention as H₂SO₄, NH₃ and VOC. The findings provide important implications for haze mitigations in China and other industrializing countries with multi-pollutant emission sources.

Fine particles at a background site in Central France: Chemical compositions, seasonal variations and pollution events

To expand our knowledge of regional fine particles in Central France (Centre-Val de Loire region), a field observation study of PM_2.5 was carried out at Verneuil site (46.81467N, 2.61012E, 180m.a.s.l.) from 2011 to 2014. The mass concentrations of water-soluble inorganic ions (WSIIs), organic carbon (OC), elemental carbon (EC) and biomass burning tracer (Levoglucosan) in PM_2.5 were measured. Annual average PM_2.5 mass concentrations were 11.8, 9.5, 12.6 and 10.2μg·m^-3 in 2011, 2012, 2013 and 2014, respectively, three of four higher than the WHO guideline of 10μg·m^-3. Secondary inorganic aerosol (SIA) and organic matter (OM) appeared to be the major components in PM_2.5 in Verneuil, contributing 30.1-41.8% and 36.9-46.3%, respectively. Main chemical species were observed in the following order: winter≥spring>autumn>summer. Backward atmospheric trajectories were performed using Hysplit model and suggested that the PM_2.5 pollutants caused by atmospheric transport were mainly originated from European inland, mainly east to north-east areas. During the observation period, five pollution events were reported and indicated that not only the polluted air masses from central Europe but also the biomass burning from East Europe significantly influenced the air quality in Verneuil site.

Seasonal Variation in Water-Soluble Ions in Airborne Particulate Deposition in the Suburban Nanjing Area, Yangtze River Delta, China, During Haze Days and Normal Days

To investigate the seasonal variation and characterization of water-soluble ions (WSIs) present in airborne particle deposition (APD) during Haze Days (visibility ≤7.5 km) and Normal Days (visibility >7.5 km) in suburban Nanjing area, 151 filter samples were collected from 18 May 2013 to 26 May 2014. Ten different WSIs from the samples were determined by Ion Chromatography. The results indicated that secondary WSIs (NH₄⁺, NO₃^-, and SO₄^2-) were the main ions in the WSIs, averaging 17.2, 18.5, and 17.1 μg/m³, respectively, and accounting respectively 20.9, 22.5, and 20.8% of the total WSIs. On Haze Days, the concentration of WSIs increased dramatically in fine size (particle size <2.1 μm), especially for NH₄⁺, NO₃^-, and SO₄^2- (increased by 52.6, 71.3, and 73.1%, respectively), whereas the concentrations of WSIs increased slowly in coarse size (2.1 μm < particle size < 10 μm), in which NH₄⁺, NO₃^-, and SO₄^2- increased by 14.7, 27.2, and 54.5%, respectively. According to the backward trajectories and the principal component analysis analysis, Nanjing APD were mainly derived from the soil dust in northern China (35%) in the spring, from ocean air masses (61 and 55%) in the summer and the autumn, and from local air masses (73%) in the winter. On summer Haze Days, secondary components in PM_2.1 consisted mainly of (NH₄)₂SO₄ and NH₄NO₃, whereas secondary components in PM_2.1-10 consisted mainly of (NH₄)₂SO₄, NH₄Cl, and NH₄NO₃. The increasing concentrations of secondary components increase the light extinction coefficients of aerosol on winter and autumn Haze Days. The concentrations of WSIs in fine size rose sharply on Haze Days, leading the visibility to exponential decline. Differently, the concentrations of WSIs in coarse size were not the main cause in the change of the visibility.

Source tagging modeling study of heavy haze episodes under complex regional transport processes over Wuhan megacity, Central China

Wuhan as a megacity of Central China was suffering from severe particulate matter pollution according to previous observation studies, however, the mechanism behind the pollution formation especially the impact of regional chemical transport is still unclear. This study, carried out on the Nested Air Quality Prediction Modeling System (NAQPMS) coupled with an on-line source-tagging module, explores different roles regional transport had in two strong haze episodes over Wuhan in October 2014 and quantitatively assesses the contributions from local and regional sources to PM_2.5 concentration. Validation of predictions based on observations shows modeling system good skills in reproducing key meteorological and chemical features. The first short-time haze episode occurred on 12 October under strong northerly winds, with a hourly PM_2.5 peak of 180 μg m^-3, and was found to be caused primarily by the long-range transport from the northern regions, which contributed 60.6% of the episode's PM_2.5 concentration (versus a total of 32.7% from sources in and near Wuhan). The second episode lasted from the 15-20 October under stable regional large-scale synoptic conditions and weak winds, and had an hourly PM_2.5 peak of 231.0 μg m^-3. In this episode, both the long-distance transport from far regions and short-range transport from the Wuhan-cluster were the primary causes of the haze episode and account for 24.8% and 29.2% of the PM_2.5 concentration respectively. Therefore, regional transport acts as a crucial driver of haze pollution over Wuhan through not only long-range transfer of pollutants, but also short-range aerosol movement under specific meteorological conditions. The present findings highlight the important role of regional transport in urban haze formation and indicate that the joint control of multi city-clusters are needed to reduce the particulate pollution level in Wuhan.

Long-term exposure to high air pollution induces cumulative DNA damages in traffic policemen

The specific effects of long-term exposure to high air pollution on human health and biological remain unclear. To explore the adverse health effects as well as biological mechanisms and biomarkers for durative exposure to air pollution, 183 traffic policemen and 88 office policemen were enrolled in this study. The concentration of PM2.5 in both the traffic and office policemen's working environments were obtained. Detailed personal questionnaires were completed and levels of inflammation, oxidative stress and DNA damage markers of all participants were analyzed in this study. The average PM2.5 concentration of the intersections of main roads and the offices of control group were 132.4±48.9μg/m³ and 50.80±38.6μg/m³, respectively. The traffic policemen, who stably exposed to at least 2 times higher PM2.5 in their work area as compared with the control group, have a median average duration of 7.00years, and average cumulative intersection duty time reached 8030h. No statistically significant differences in the levels of inflammation markers were observed between the traffic and office policemen. However, the DNA damage markers in traffic policemen shared significant positive correlation with cumulative intersection duty time and higher than those in the office policemen. Multiple linear regression analysis demonstrated that the increase of cumulative intersection duty time by 1h per day for one year was associated with the increase in 8-hydroxy-20-deoxyguanosine of 0.329% (95% CI: 0.249% to 0.409%), tail DNA of 0.051% (95% CI: 0.041% to 0.061%), micronucleus frequency of 0.036‰ (95% CI: 0.03‰ to 0.043‰), and a decrease in glutathione of 0.482% (95% CI: -0.652% to -0.313%). These findings suggest that long-term exposure to high air pollution could induce cumulative DNA damages, supporting the hypothesis that durative exposure to air pollution is associated with an increased risk of cancer.

Fine particulate matter 2.5 exerted its toxicological effect by regulating a new layer, long non-coding RNA

Fine particulate matter (PM2.5) exposure, especially to its organic components, induces adverse health effects on the respiratory system. However, the molecular mechanisms have still not been fully elucidated. Long non-coding RNA (lncRNA) is involved in various physio-pathological processes. In this study, the roles of lncRNA were investigated to reveal the toxicology of PM2.5. Organic extracts of PM2.5 from Nanjing and Shanghai cities were adopted to treat human bronchial epithelial cell lines (BEAS-2B and A549). RNA sequencing showed that the lncRNA functioned as antisense RNA, intergenic RNA and pre-miRNA. The mRNA profiles were also altered after exposure. PM2.5 from Nanjing showed a more serious impact than that from Shanghai. In detail, higher expression of n405968 was positively related to the elevated mRNA levels of inflammatory factors (IL-6 and IL-8). Increasing levels of metastasis associated lung adenocarcinoma transcript 1 (MALAT1) were positively associated with the induced epithelial-mesenchymal transition (EMT) process. Similar response was observed between both cell lines. The higher content of polycyclic aromatic hydrocarbons (PAHs) is likely to contribute to higher toxicity of PM2.5 from Nanjing than that from Shanghai. Antagonism of aryl hydrocarbon receptor (AHR) or inhibition of CYP1A1 diminished the effects stimulated by PM2.5. Our results indicated that lncRNAs could be involved in the toxicology of PM2.5 through regulating the inflammation and EMT process.

Seasonal variations and source apportionment of atmospheric PM2.5-bound polycyclic aromatic hydrocarbons in a mixed multi-function area of Hangzhou, China

To reveal the seasonal variations and sources of PM_2.5-bound polycyclic aromatic hydrocarbons (PAHs) during haze and non-haze episodes, daily PM_2.5 samples were collected from March 2015 to February 2016 in a mixed multi-function area in Hangzhou, China. Ambient concentrations of 16 priority-controlled PAHs were determined. The sums of PM_2.5-bound PAH concentrations during the haze episodes were 4.52 ± 3.32 and 13.6 ± 6.29 ng m^-3 in warm and cold seasons, respectively, which were 1.99 and 1.49 times those during the non-haze episodes. Four PAH sources were identified using the positive matrix factorization model and conditional probability function, which were vehicular emissions (45%), heavy oil combustion (23%), coal and natural gas combustion (22%), and biomass combustion (10%). The four source concentrations of PAHs consistently showed higher levels in the cold season, compared with those in the warm season. Vehicular emissions were the most considerable sources that result in the increase of PM_2.5-bound PAH levels during the haze episodes, and heavy oil combustion played an important role in the aggravation of haze pollution. The analysis of air mass back trajectories indicated that air mass transport had an influence on the PM_2.5-bound PAH pollution, especially on the increased contributions from coal combustion and vehicular emissions in the cold season.

Characteristics and origins of air pollutants in Wuhan, China, based on observations and hybrid receptor models

To identify the characteristics of air pollutants and factors attributing to the formation of haze in Wuhan, this study analyzed the hourly observations of air pollutants (PM_2.5, PM₁₀, NO₂, SO₂, O₃, and CO) from March 1, 2013, to February 28, 2014, and used hybrid receptor models for a case study. The results showed that the annual average concentrations for PM_2.5, PM₁₀, NO₂, SO₂, O₃, and CO during the whole period were 89.6 μg m^-3, 134.9 μg m^-3, 54.9 μg m^-3, 32.4 μg m^-3, 62.3 μg m^-3, and 1.1 mg m^-3, respectively. The monthly variations revealed that the peak values of PM_2.5, PM₁₀, NO₂, SO₂, and CO occurred in December because of increased local emissions and severe weather conditions, while the lowest values occurred in July mainly due to larger precipitation. The maximum O₃ concentrations occurred in warm seasons from May to August, which may be partly due to the high temperature and solar radiation. Diurnal analysis showed that hourly PM_2.5, PM₁₀, NO₂, and CO concentrations had two ascending stages accompanying by the two traffic peaks. However, the O₃ concentration variations were different with the highest concentration in the afternoon. A case study utilizing hybrid receptor models showed the significant impact of regional transport on the haze formation in Wuhan and revealed that the mainly potential polluted sources were located in the north and south of Wuhan, such as Baoding and Handan in Hebei province, and Changsha in Hunan province.

IMPLICATIONS

Wuhan city requires a 5% reduction of the annual mean of PM_2.5 concentration by the end of 2017. In order to accomplish this goal, Wuhan has adopted some measures to improve its air quality. This work has determined the main pollution sources that affect the formation of haze in Wuhan by transport. We showed that apart from the local emissions, north and south of Wuhan were the potential sources contributing to the high PM_2.5 concentrations in Wuhan, such as Baoding and Handan in Hebei province, Zhumadian and Jiaozuo in Henan province, and Changsha and Zhuzhou in Hunan province.

Mass extinction efficiency and extinction hygroscopicity of ambient PM2.5 in urban China

The ambient PM_2.5 pollution problem in China has drawn substantial international attentions. The mass extinction efficiency (MEE) and hygroscopicity factor (f(RH)) of PM_2.5 can be readily applied to study the impacts on atmospheric visibility and climate. The few previous investigations in China only reported results from pilot studies and are lack of spatial representativeness. In this study, hourly average ambient PM_2.5 mass concentration, relative humidity, and atmospheric visibility data from China national air quality and meteorological monitoring networks were retrieved and analyzed. It includes 24 major Chinese cities from nine city-clusters with the period of October 2013 to September 2014. Annual average extinction coefficient in urban China was 759.3±258.3Mm^-1, mainly caused by dry PM_2.5 (305.8.2±131.0Mm^-1) and its hygroscopicity (414.6±188.1Mm^-1). High extinction coefficient values were resulted from both high ambient PM_2.5 concentration (68.5±21.7µg/m³) and high relative humidity (69.7±8.6%). The PM_2.5 mass extinction efficiency varied from 2.87 to 6.64m²/g with an average of 4.40±0.84m²/g. The average extinction hygroscopic factor f(RH=80%) was 2.63±0.45. The levels of PM_2.5 mass extinction efficiency and hygroscopic factor in China were in comparable range with those found in developed countries in spite of the significant diversities among all 24 cities. Our findings help to establish quantitative relationship between ambient extinction coefficient (visual range) and PM_2.5 & relative humidity. It will reduce the uncertainty of extinction coefficient estimation of ambient PM_2.5 in urban China which is essential for the research of haze pollution and climate radiative forcing.

Review of receptor-based source apportionment research of fine particulate matter and its challenges in China

As the key for haze control, atmospheric fine particulate matter with aerodynamic diameter <2.5μm (or PM_2.5) is of great concern lately in China. It is closely linked to fast pace of urbanization, industrialization and economic development, especially in eastern China. A good understanding of its sources is required for effective pollution abatement. Receptor models are one of the major methods for source apportionment used in China. The major objective of this study is to understand sources that contribute to fine particulate matter in China and key challenges in this area. Spatial distribution of fine particulate matter concentration, chemical composition and dominant sources in North and South China are summarized. Based on chemical speciation results from 31 cities and source apportionment results from 21 cities, it is found that secondary sources and traffic emission have higher contribution in South China while the percentage of coal combustion, dust and biomass burning to total PM_2.5 are higher in North China. Source profiles established in China from 44 cities and areas are also summarized as references for future source apportionment studies. Suggestions for future research are also provided including methods for evaluating source apportionment results, ways for integrating multiple source apportionment methods, the need for standardizing protocols and developing tools for high-time resolution source apportionment.

Source apportionment and a novel approach of estimating regional contributions to ambient PM2.5 in Haikou, China

A novel approach was developed to estimate regional contributions to ambient PM_2.5 in Haikou, China. In this paper, the investigation was divided into two main steps. The first step: analysing the characteristics of the chemical compositions of ambient PM_2.5, as well as the source profiles, and then conducting source apportionments by using the CMB and CMB-Iteration models. The second step: the development of estimation approaches for regional contributions in terms of local features of Haikou and the results of source apportionment, and estimating regional contributions to ambient PM_2.5 in Haikou by this new approach. The results indicate that secondary sulphate, resuspended dust and vehicle exhaust were the major sources of ambient PM_2.5 in Haikou, contributing 9.9-21.4%, 10.1-19.0% and 10.5-20.2%, respectively. Regional contributions to ambient PM_2.5 in Haikou in spring, autumn and winter were 22.5%, 11.6% and 32.5%, respectively. The regional contribution in summer was assumed to be zero according to the better atmospheric quality and assumptions of this new estimation approach. The higher regional contribution in winter might be mainly attributable to the transport of polluted air originating in mainland China, especially from the north, where coal is burned for heating in winter.

PM2.5 Exposure Suppresses Dendritic Maturation in Subgranular Zone in Aged Rats

Detrimental effects of long-term inhalation of fine particulate matter (PM_2.5) on the pulmonary and cardiovascular systems have been widely reported. Recent studies have shown that exposure to PM_2.5 also causes adverse neurocognitive effects. This study investigates the effects of inhaled ammonium sulfate, which is a major compound of inorganic air pollutants in PM_2.5, on adult neurogenesis in aged Sprague-Dawley rats. A total of 20 rats were randomly assigned to experimental (n = 10) and control (n = 10) conditions, wherein they were exposed to either ammonium sulfate or sham air for 2 h per day and for 28 consecutive days. It was observed that ammonium sulfate inhibited the maturation process and diminished dendritic complexity of immature neurons in the subgranular zone (SGZ) of the hippocampus significantly, although the number of neural stem cells or the rates of differentiation were comparable between the two groups. Our findings provide clear evidence on the direct relationship between air quality and advantageous neurogenesis. Exposure to PM leads to specific adverse effects on the maturation process during neurogenesis.

Characterization and source apportionment of PM2.5 based on error estimation from EPA PMF 5.0 model at a medium city in China

Heze city, a medium-size city in Shandong province, Eastern China. Ambient PM_2.5 samples were collected in urban area of Heze from August 2015 to April 2016, and chemical species and sources of PM_2.5 were investigated in this paper. The results indicated that the average concentration of PM_2.5 was 100.9 μg/m³ during the sampling period, and the water-soluble ions, carbonaceous species included elemental carbon (EC) and organic carbon (OC), as well as elements contributed 32.7-51.7%, 16.3% and 12.5%, respectively, to PM_2.5. Pearson's correlation analysis showed that the existing form of NH₄⁺ was more complex and diverse in spring/summer, and ammonium nitrate, ammonium sulfate and ammonium hydrogen sulfate might be major form of NH₄⁺ in autumn/winter. Correlation analysis between PM_2.5 and SO₄^2-/NO₃^-, PM_2.5 and OC/EC during different seasons suggested that mobile sources might make an important impact on the increase of PM_2.5 concentrations in spring/summer, and stationary sources might play a critical role on the increase of PM_2.5 concentrations in autumn/winter. Seven factors were selected in Positive Matrix Factorization (PMF) models analysis based on the Error Estimation (EE) diagnostics during different seasons. Secondary source had the highest contribution to PM_2.5 in Heze for the whole year, and followed by coal combustion, vehicle exhaust, soil dust, construction dust, biomass burning and metal manufacturing, and their annual contributions to PM_2.5 were 26.5%, 17.2%, 16.5%, 11.5%, 7.7%, 7.0% and 3.8%, respectively. The air masses that were originated from Mongolia reflected the features of large-scale and long-distance air transport; while the air masses that began in Jiangsu, Shandong and Henan showed the features of small-scale and short-distance. Shandong, Henan and Jiangsu were identified as the major potential sources-areas of PM_2.5 by using potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) models.

Influence of fireworks displays on the chemical characteristics of PM2.5 in rural and suburban areas in Central and East China

To explore the spatial and chemical characteristics of PM_2.5 pollution and the influence of fireworks displays on PM_2.5 and its chemical components in rural areas in Central and East China, PM_2.5 samples were collected at three rural sites and one suburban site in Henan and Shandong provinces during the 2016 Chinese New Year, and the chemical composition of PM_2.5, including water-soluble inorganic ions (WSIIs), organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC) and trace elements (TEs) was analysed. The concentrations of PM_2.5 at the four sites were significantly higher than the Grade I national standard of 35μg/m³, indicating serious PM_2.5 pollution in rural and suburban areas. The contributions of secondary WSIIs to total WSIIs at the four sites were lower than in urban areas. The TEs in XP and LC were significantly enriched in PM_2.5. A significant difference was found in the main chemical compositions of different sites. Fireworks displays directly increased the concentrations of PM_2.5 and many chemicals, especially K⁺, Cl^-, K, Cl, S, Cu and Sr, and concentrations of NO₃^- and NH₄⁺ ions peaked after the fireworks period in the three rural sites, indicating the influence of firecrackers on the secondary formation of the precursors of NO₂. The ratio of WSOC/OC decreased during fireworks displays, indicating the direct influence of firecrackers on water insoluble organic matter. Fireworks-related ions were a key component of the aerosol at the four sites during fireworks displays, accounting for 28-38% of the total measured species.

Detecting the causality influence of individual meteorological factors on local PM2.5 concentration in the Jing-Jin-Ji region

Due to complicated interactions in the atmospheric environment, quantifying the influence of individual meteorological factors on local PM_2.5 concentration remains challenging. The Beijing-Tianjin-Hebei (short for Jing-Jin-Ji) region is infamous for its serious air pollution. To improve regional air quality, characteristics and meteorological driving forces for PM_2.5 concentration should be better understood. This research examined seasonal variations of PM_2.5 concentration within the Jing-Jin-Ji region and extracted meteorological factors strongly correlated with local PM_2.5 concentration. Following this, a convergent cross mapping (CCM) method was employed to quantify the causality influence of individual meteorological factors on PM_2.5 concentration. The results proved that the CCM method was more likely to detect mirage correlations and reveal quantitative influences of individual meteorological factors on PM_2.5 concentration. For the Jing-Jin-Ji region, the higher PM_2.5 concentration, the stronger influences meteorological factors exert on PM_2.5 concentration. Furthermore, this research suggests that individual meteorological factors can influence local PM_2.5 concentration indirectly by interacting with other meteorological factors. Due to the significant influence of local meteorology on PM_2.5 concentration, more emphasis should be given on employing meteorological means for improving local air quality.

Mortality effects assessment of ambient PM2.5 pollution in the 74 leading cities of China

BACKGROUND

Ambient fine particulate matter (PM2.5) pollution is currently a most severe and worrisome environmental problem in China. However, current knowledge of the health effects of this pollution is insufficient.

OBJECTIVES

This study aims to provide an overall understanding regarding the long-term mortality effects of current PM2.5 pollution in China and the potential health benefits of realizing the goals stipulated in the ongoing action plan of Air Pollution Prevention and Control (APPC) and the targets suggested by the WHO.

METHODS

Three typical causes and all-cause of PM2.5-related mortality were considered. The log-linear exposure-response function was adopted, and a meta-analysis was used to determine the exposure-response coefficients, based on newly available data in China and abroad.

RESULTS

In the 74 leading cities of China, approximately 32% of the reported deaths, with a mortality rate of 1.9‰, were associated with PM2.5 in 2013, in which deaths from cardiovascular, respiratory and lung-cancer causes accounted for 20% of the reported deaths, with a mortality rate of 1.2‰. The regional difference is remarkable for the mortalities and proportions of the different causes. If the PM2.5 concentration goals of the APPC plan, the first interim and the guideline targets of the WHO could be achieved, the PM2.5-related all-cause mortality would be reduced by 25%, 64% and 95%, respectively, compared with that of 2013.

CONCLUSIONS

PM2.5 pollution in China has incurred great health risks that are even worse than those of tobacco smoking. The health benefits of the APPC plan could be outstanding, although there is still great potential to improve future air quality.

Seasonal and spatial differences in source contributions to PM2.5 in Wuhan, China

Fine particle (PM2.5) samples were collected in 2011 and 2012 simultaneously at three sites in Wuhan in an industrial area (ID), downtown Wuhan (DT), and the Wuhan botanical gardens (BG). The annual average concentration of PM2.5 was highest in the industrial area at 180μgm-3 and lowest in the botanical gardens, with an average of 93μgm-3. The average downtown PM2.5 concentration was 113μgm-3. All sites had concentrations well above the World Health Organization (WHO) guidelines and the Chinese air quality standard. The concentration of major constituents of PM2.5 varied seasonally across all sites; specifically, sulfate, nitrate, and organic carbon varied most strongly during spring, followed by summer and fall. Organic carbon varied the most across sites for all seasons, which is attributable to large differences in local source emissions. The major primary sources contributing to OC were vehicle emissions (38.1±8.3%), coal combustion (7.0±6.2%), meat cooking (3.0±1.6%), and biomass burning (3.0±1.0%). All these sources had large seasonal variations across the three sites. Biomass burning had the largest impact at BG, mobile sources had the largest impact at DT, and coal combustion had the largest impact at ID. Mineral dust was a major contributor to PM2.5 (average 16.8±9.6μgm-3) and had very homogenous concentrations across the sites during springtime due to regional dust storms, but had much higher concentration at ID during the summer and fall. The results demonstrate the need for both regional and local air pollution control strategies to reduce air pollution in Wuhan. This research contributes to the field of particulate matter studies by providing information about seasonal and regional fluctuations in PM2.5 in large urban areas, which helps advance understanding of the sources responsible for urban haze.

Status and characteristics of ambient PM2.5 pollution in global megacities

Ambient PM2.5 pollution is a substantial threat to public health in global megacities. This paper reviews the PM2.5 pollution of 45 global megacities in 2013, based on mass concentration from official monitoring networks and composition data reported in the literature. The results showed that the five most polluted megacities were Delhi, Cairo, Xi'an, Tianjin and Chengdu, all of which had an annual average concentration of PM2.5 greater than 89μg/m(3). The five cleanest megacities were Miami, Toronto, New York, Madrid and Philadelphia, the annual averages of which were less than 10μg/m(3). Spatial distribution indicated that the highly polluted megacities are concentrated in east-central China and the Indo-Gangetic Plain. Organic matter and SNA (sum of sulfate, nitrate and ammonium) contributed 30% and 36%, respectively, of the average PM2.5 mass for all megacities. Notable seasonal variation of PM2.5 polluted days was observed, especially for the polluted megacities of China and India, resulting in frequent heavy pollution episodes occurring during more polluted seasons such as winter. Marked differences in PM2.5 pollution between developing and developed megacities require more effort on local emissions reduction as well as global cooperation to address the PM2.5 pollution of those megacities mainly in Asia.