Non-haze Days Research Articles

Diversity and Composition of Airborne Fungal Community Associated with Particulate Matters in Beijing during Haze and Non-haze Days.

To assess the diversity and composition of airborne fungi associated with particulate matters (PMs) in Beijing, China, a total of 81 PM samples were collected, which were derived from PM2.5, PM10 fractions, and total suspended particles during haze and non-haze days. The airborne fungal community in these samples was analyzed using the Illumina Miseq platform with fungi-specific primers targeting the internal transcribed spacer 1 region of the large subunit rRNA gene. A total of 797,040 reads belonging to 1633 operational taxonomic units were observed. Of these, 1102 belonged to Ascomycota, 502 to Basidiomycota, 24 to Zygomycota, and 5 to Chytridiomycota. The dominant orders were Pleosporales (29.39%), Capnodiales (27.96%), Eurotiales (10.64%), and Hypocreales (9.01%). The dominant genera were Cladosporium, Alternaria, Fusarium, Penicillium, Sporisorium, and Aspergilus. Analysis of similarities revealed that both particulate matter sizes (R = 0.175, p = 0.001) and air quality levels (R = 0.076, p = 0.006) significantly affected the airborne fungal community composition. The relative abundance of many fungal genera was found to significantly differ among various PM types and air quality levels. Alternaria and Epicoccum were more abundant in total suspended particles samples, Aspergillus in heavy-haze days and PM2.5 samples, and Malassezia in PM2.5 samples and heavy-haze days. Canonical correspondence analysis and permutation tests showed that temperature (p < 0.01), NO2 (p < 0.01), PM10 (p < 0.01), SO2(p < 0.01), CO (p < 0.01), and relative humidity (p < 0.05) were significant factors that determine airborne fungal community composition. The results suggest that diverse airborne fungal communities are associated with particulate matters and may provide reliable data for studying the responses of human body to the increasing level of air pollution in Beijing.

Characteristics of atmospheric particulate mercury in size-fractionated particles during haze days in Shanghai

Atmospheric particulate mercury (PHg) is recognized as a global pollutant that requires regulation because of its significant impacts on both human health and wildlife. The haze episodes that occur frequently in China could influence the transport and fate of PHg. To examine the characteristics of PHg during haze and non-haze days, size-fractioned particles were collected using thirteen-stage Nano-MOUDI samplers (10 nm–18 μm) during a severe haze episode (from December 2013 to January 2014) in Shanghai. The PHg concentration on haze days (4.11 ± 0.53 ng m−3) was three times higher than on non-haze days (1.34 ± 0.15 ng m−3). The ratio of the PHg concentration to total gaseous mercury (TGM) ranged from 0.42 during haze days to 0.21 during non-haze days, which was possibly due to the elevated concentration of particles for gaseous elemental mercury (GEM) adsorption, elevated sulfate and nitrate contributing to GEM oxidation, and the catalytic effect of elevated water-soluble inorganic metal ions. PHg/PM10 during haze days (0.019 ± 0.004 ng/μg) was lower than during non-haze days (0.024 ± 0.002 ng/μg), and PHg/PM10 was significantly reduced with an increasing concentration of PM10, which implied a relatively lower growth velocity of mercury than other compositions on particles during haze days, especially in the diameter range of 0.018–0.032 μm.During haze days, each size-fractioned PHg concentration was higher than the corresponding fraction on non-haze days, and the dominant particle size was in the accumulation mode, with constant accumulation to a particle size of 0.56–1.0 μm. The mass size distribution of PHg was bimodal with peaks at 0.32–0.56 μm and 3.1–6.2 μm on non-haze days, and 0.56–1.0 μm and 3.1–6.2 μm on haze days. There was a clear trend that the dominant size for PHg in the fine modes shifted from 0.32–0.56 μm during non-haze days to 0.56–1.0 μm on haze days, which revealed the higher growth velocity of PHg on haze days due to the condensation and accumulation of Hg in particles. Traffic emissions and coal combustion may contribute to the high concentrations of Hg, because PHg of every size was found to correlate positively with SO2, NO2, and CO. A correlation was found between every mode of PHg and relative humidity, which affected the gas-particle partitioning of semi-volatile organic compounds, resulting in effective partitioning into aerosols. The strong correlations between Hg and water-soluble ions implied the oxidation of elemental Hg was the main gas-to-particle chemical transformation process.

Concentrations and chemical compositions of fine particles (PM2.5) during haze and non-haze days in Beijing

To investigate the chemical properties of PM2.5 and put forward reasonable control measures, daily samples of PM2.5 were collected at an urban site in Beijing from August 4 to September 3 of 2012 using two 2-channel samplers. Chemical analysis was conducted for eight water soluble inorganic ions (WSII, including Na+, NH4+, K+, Mg2+, Ca2+, Cl−, NO3−, and SO42−), organic carbon (OC) and elementary carbon (EC). PM2.5 concentrations ranged from 8.8 to 218.6μgm−3, with an average concentration of 80.6±57.3μgm−3. WSII, the most dominant PM2.5 constituents contributing 60±18% of its mass, ranged from 3.1 to 172.2μgm−3. SO42−, NO3−, and NH4+ dominated WSII (90±28%) and their concentrations were 1.3–105.7μgm−3, 0.5–52.7μgm−3 and 0.3–33.5μgm−3, respectively. The concentrations of OC and EC were 3.0–28.8 μgC m−3 and 0.8–7.4 μgC m−3, constituting 17.6% and 4.9% of PM2.5, respectively. Three serious pollution episodes (haze days) occurred during the campaign. PM2.5 and its chemical species showed substantial increases during haze episodes. The greater enhancement factors for SO42− (4.5), NO3− (4.0), and NH4+ (4.2) during haze days compared to non-haze days were obtained, suggesting that these secondary inorganic ions play important roles in the formation of haze. The average ratio of NO3−/SO42− was 0.52. Ion balance calculations showed that PM2.5 samples were acidic during haze periods and close to neutral during non-haze days. Correlation analysis between the major ions was conducted and the results suggested that the main forms of NH4+ might be (NH4)2SO4. In addition, the variations between haze days and non-haze days for OC, EC, and the ratio of OC/EC were discussed.

Size-resolved source apportionment of particulate matter in urban Beijing during haze and non-haze episodes

Abstract. Additional size-resolved chemical information is needed before the physicochemical characteristics and sources of airborne particles can be understood; however, this information remains unavailable in most regions of China due to lacking measurement data. In this study, we report observations of various chemical species in size-segregated particle samples that were collected over 1 year in the urban area of Beijing, a megacity that experiences severe haze episodes. In addition to fine particles, high concentrations of coarse particles were measured during the periods of haze. The abundance and chemical compositions of the particles in this study were temporally and spatially variable, with major contributions from organic matter and secondary inorganic aerosols. The contributions of organic matter to the particle mass decreased from 37.9 to 31.2 %, and the total contribution of sulfate, nitrate and ammonium increased from 19.1 to 33.9 % between non-haze and haze days, respectively. Due to heterogeneous reactions and hygroscopic growth, the peak concentrations of the organic carbon, cadmium and sulfate, nitrate, ammonium, chloride and potassium shifted from 0.43 to 0.65 µm on non-haze days to 0.65–1.1 µm on haze days. Although the size distributions of lead and thallium were similar during the observation period, their concentrations increased by a factor of more than 1.5 on haze days compared with non-haze days. We observed that sulfate and ammonium, which have a size range of 0.43–0.65 µm, sulfate and nitrate, which have a size range of 0.65–1.1 µm, calcium, which has a size range of 5.8–9 µm, and the meteorological factors of relative humidity and wind speed were responsible for haze pollution when the visibility was less than 10 km. Source apportionment using Positive Matrix Factorization showed six PM2.1 sources and seven PM2.1–9 common sources: secondary inorganic aerosol (25.1 % for fine particles vs. 9.8 % for coarse particles), coal combustion (17.7 % vs. 7.8 %), biomass burning (11.1 % vs. 11.8 %), industrial pollution (12.1 % vs. 5.1 %), road dust (8.4 % vs. 10.9 %), vehicle emissions (19.6 % for fine particles), mineral dust (22.6 % for coarse particles) and organic aerosol (23.6 % for coarse particles). The contributions of the first four factors and vehicle emissions were higher on haze days than non-haze days, while the reverse is true for road dust and mineral dust. The sources' contribution generally increased as the size decreased, with the exception of mineral dust. However, two peaks were consistently found in the fine and coarse particles. In addition, the sources' contribution varied with the wind direction, with coal and oil combustion products increasing during southern flows. This result suggests that future air pollution control strategies should consider wind patterns, especially during episodes of haze. Furthermore, the findings of this study indicated that the PM2.5-based data set is insufficient for determining source control policies for haze in China and that detailed size-resolved information is needed to characterize the important sources of particulate matter in urban regions and better understand severe haze pollution.

Characteristics of Haze Pollution Episodes and Analysis of a Typical Winter Haze Process in Shanghai

ABSTRACTOne-year field campaign was conducted from July 2013 to August 2014 at the site of East China University of Science and Technology (ECUST) in urban Shanghai, and mass concentrations and chemical compositions of PM2.5 were measured. Gaseous pollutants (SO2, NO2) and meteorological parameters (wind speed, wind direction, pressure, temperature and relative humidity) were simultaneously obtained. In this study, PM2.5 mass balances on haze and non-haze days were reconstructed and the sum of secondary inorganic aerosols (SIA) and organic matter (OM) accounted for over 80%. The fraction of nitrate in SIA was much higher on haze days than that on non-haze days, while the corresponding fraction of ammonium was lower, implying that the variations of the sources and formation processes of SIA on haze days. In theory, sulfate and nitrate might be almost fully neutralized by ammonium. Moreover, the sulfur oxidation ratio (SOR) values were much higher than the nitrogen oxidation ratio (NOR) values, indicating the greater oxidation capacity of SO2 would occur. On haze days, the high NOR values could be explained by the relatively low temperature, the high NO2 concentration and the potential dominant gas-phase reaction. As for secondary organic aerosol (SOA), the formation processes were usually associated with nitrate formation. In winter, haze pollution episodes occurred more frequently than those in other seasons, associated with the different features of wind speed, wind direction and 72-h backward trajectory. In addition, one case from 17 November 2013 to 4 January 2014 was selected to investigate the formation mechanism of haze pollution episodes. The key factors that affected the haze formation might be the local stable synoptic conditions including weak surface wind, surface temperature inversion and high relative humidity, the long-range transportations from the Northwest and the large amounts of emissions from local sources.

A Key Indicator of Transboundary Particulate Matter Pollution Derived from Indonesian Peatland Fires in Malaysia

ABSTRACTWe characterized ambient total suspended particulates (TSP) based on ground-based samplings in Malaysia during non-haze days and haze ones affected by Indonesian peatland fires. Furthermore, a key indicator of Indonesian peatland fire was determined based on chemical characterization of TSP in Malaysia. TSP samples were chemically analyzed to determine organic carbon (OC), elemental carbon (EC), inorganic ions, and biomarkers (solvent-extractable organic compounds derived from biomass burning). Regarding OC and EC, concentrations of OC1 and OP (pyrolyzed OC) defined by IMPROVE_A protocol increased remarkably during the haze episodes. On the contrary, there were no significant differences in concentrations of OC4, EC, and EC fractions between the haze and non-haze samples. Regarding inorganic ions, sulfate and ammonium concentrations increased in strong haze days, however, it is difficult to use these compounds as indicators for Indonesian peatland fires in light haze days due to the partial overlapping of the variation ranges of sulfate and ammonium concentrations in non-haze days. Concentrations of many biomarkers derived from cellulose, hemicellulose, and lignin pyrolysis products were significantly increased during strong haze days but not during light haze days except p-hydroxybenzoic acid. We proposed the OP to OC4 ratio as a potential indicator of transboundary haze pollution from Indonesian peatland fires at the receptor sites even in light haze.

The mercury species and their association with carbonaceous compositions, bromine and iodine in PM2.5 in Shanghai.

PM2.5 samples were collected in south Shanghai from November 2013 to October 2014. The species of particulate bounded mercury (PBM), including hydrochloric soluble particle-phase mercury (HPM), element soluble particle-phase mercury (EPM) and residual soluble particle-phase mercury (RPM), were determined in PM2.5. The chemical composition of PM2.5 including organic carbon (OC) and elemental carbon (EC), total bromine and iodine were also analyzed. The results showed that the annual average concentration of PBM was 0.30 ± 0.31 ng m(-3) and 0.34 ± 0.32 ng m(-3) in winter, 0.31 ± 0.19 ng m(-3) in spring, 0.30 ± 0.45 ng m(-3) in fall and 0.28 ± 0.17 ng m(-3) in summer. HPM took the highest fraction 51.2% in PBM, followed by RPM 27.7% and EPM 21.1%. EC positively correlated to particle mercury, especially in winter (r = 0.70), the same for OC in winter (r = 0.72), which indicated that the carbonaceous composition may affect the transformation of Hg in the atmosphere. Mercury species showed different correlations with bromine and iodine in the four seasons. The strongest correlation between bromine, iodine and mercury was found in spring and fall, respectively. Bromine showed the stronger correlation with total mercury and speciated particle mercury than iodine. In addition, the days were classified into haze and non-haze days based on the visibility and relative humidity, while the ratio of HPM in haze days was much higher than that in non-haze days. EC strongly correlated with PBM during haze and non-haze days while OC only positively correlated with PBM in non-haze days, this may indicate that the different carbonaceous part may affect PBM differently.

Source apportionment of Beijing air pollution during a severe winter haze event and associated pro-inflammatory responses in lung epithelial cells

Abstract Air pollution is a leading risk factor for the disease burden in China and globally. Few epidemiologic studies have characterized the particulate matter (PM) components and sources that are most responsible for adverse health outcomes, particularly in developing countries. In January 2013, a severe haze event occurred over 25 days in urban Beijing, China. Ambient fine particulate matter (PM2.5) was collected at a central urban site in Beijing from January 16-31, 2013. We analyzed the samples for water soluble ions, metals, elemental carbon (EC), organic carbon (OC), and individual organic molecular markers including n-alkanes, hopanes, PAHs and sterols. Chemical components were used to quantify the source contributions to PM2.5 using the chemical mass balance (CMB) model by the conversion of the OC estimates combined with inorganic secondary components (e.g. NH4+, SO42−, NO3-). Water extracts of PM were exposed to lung epithelial cells, and supernatants recovered from cell cultures were assayed for the pro-inflammatory cytokines by a quantitative ELLSA method. Linear regression models were used to estimate the associations between PM sources and components with pro-inflammatory responses in lung epithelial cells following 24-hrs and 48-hrs of exposure. The largest contributors to PM2.5 during the monitoring period were inorganic secondary ions (53.2% and 54.0% on haze and non-haze days, respectively). Other organic matter (OM) contributed to a larger proportion of PM2.5 during haze days (16.9%) compared with non-haze days (12.9%), and coal combustion accounted for 10.9% and 8.7% on haze and non-haze days, respectively. We found PM2.5 mass and specific sources (e.g. coal combustion, traffic emission, dust, other OM, and inorganic secondary ions) were highly associated with inflammatory responses of lung epithelial cells. Our results showed greater responses in the exposure to 48-hr PM2.5 mass and its sources compared to 24-hr PM exposure, and that secondary and coal combustion sources play an important role in short-term inflammation and require cost-effective policy to control their contributions to air pollution.

Mercury concentration in fine atmospheric particles during haze and non-haze days in Shanghai, China

Concentrations of fine particulate mercury (PHg), particulate matter ≤2.5 μm (PM2.5), and particulate matter ≤10 μm (PM10) were monitored for the whole year of 2013 in Shanghai, China. The average concentrations of PHg were 1270 ± 716 pg/m3 and 341 ± 187 pg/m3 during haze and non-haze days respectively. The average PHg concentration throughout the whole year 2013 was 642 ± 616pg/m3. It was observed that PHg concentrations on haze days were 3 times higher than on non-haze days. The concentration of PHg on non-haze days in 2013 varied from 0.25 to 0.48 ng/m3. The mean monthly PHg concentration was highest in December (1.92 ng/m3), while the minimum mean concentration was observed in February and August (0.80 ng/m3), and there was a clear seasonal variation: winter (1.67 ng/m3), autumn (1.08 ng/m3), spring (1.02 ng/m3), and summer (1.00 ng/m3) during haze days. The correlation between PHg and PM2.5 was strong (r = 0.96 on haze days; r = 0.90 on non-haze days), while the correlation between PHg and PM10 was weaker (r = 0.85 on haze days; r = 0.57 on non-haze days). The PHg concentration on haze days was always higher than on non-haze days, indicating that haze conditions were accelerating the formation of PHg. The result also indicated that PHg was inclined to combine with fine particles. The existence of strong correlations between the concentrations of PM2.5, PM10, and PHg indicated the commonality of the contributing sources, such as traffic, industrial emissions, and the combustion of coal.

Characteristics of bacterial and fungal aerosols during the autumn haze days in Xi'an, China

Abstract In recent years, haze pollution has become one of the most critical environmental issues in Xi'an, China, with particular matter (PM) being one of the top pollutants. As an important fraction of PM, bioaerosols may have adverse effects on air quality and human health. In this study, to better understand the characteristics of such biological aerosols, airborne microbial samples were collected by using an Andersen six-stage sampler in Xi'an from October 8th to 22nd, 2014. The concentration, size distribution and genera of airborne viable bacteria and fungi were comparably investigated during the haze days and non-haze days. Correlations of bioaerosol levels with meteorological parameters and PM concentrations were also examined. The results showed that the daily average concentrations of airborne viable bacteria and fungi during the haze days, 1102.4–1736.5 and 1466.2–1703.9 CFU/m3, respectively, were not only much higher than those during the non-haze days, but also exceeded the recommended permissible limit values. Comparing to size distributions during the non-haze days, slightly different patterns for bacterial aerosols and similar single-peak distribution pattern for fungal aerosols were observed during the haze days. Moreover, more allergic and infectious genera (e.g. Neisseria, Aspergillus, and Paecilomyces) in bioaerosols were identified during the haze days than during non-haze days. The present results reveal that bioaerosols may have more significant effects on public health and urban air quality during the haze days than during non-haze days.

Seasonal size distribution of airborne culturable bacteria and fungi and preliminary estimation of their deposition in human lungs during non-haze and haze days

In recent years, haze events in Beijing have significantly increased in frequency. On haze days, airborne microorganisms are considered to be a potential risk factor for various health concerns. However, limited information on bioaerosols has prevented our proper understanding of the possible threat to human health due to these bioaerosols. In this study, we used a six-stage impactor for sampling culturable bioaerosols and the LUDEP 2.07 computer-based model for calculating their deposition on human lungs to investigate seasonal concentration, size distribution, and corresponding deposition efficiency and flux in the human respiratory tract during different haze-level events. The current results of the analysis of 398 samples over four seasons indicate that the concentration of culturable airborne bacteria decreased with increasing haze severity. The bioaerosol concentration ratio was skewed towards larger particle sizes on heavy haze days leading to larger bioaerosol aerodynamic diameters than on non-haze days. During nasal breathing by an adult male engaged in light exercise in an outdoor environment, the total deposition efficiency of culturable bioaerosols is 80–90% including approximately 70% in the upper respiratory tract, 5–7% in the alveoli, and about 3% in the bronchial couple with bronchiolar regions. Although the difference in culturable bioaerosol aerodynamic diameters at different haze levels was not large enough to cause obvious differences in lung deposition efficiency, the deposition fluxes clearly varied with the degree of haze owing to the varied concentration of culturable airborne bacteria and fungi. The results here could improve our understanding of the seasonal health threat due to culturable bioaerosols during non-haze and haze days.

Carbonyl compounds over urban Beijing: Concentrations on haze and non-haze days and effects on radical chemistry

Carbonyl compounds play an important role in the formation of secondary aerosols and the cycling of free radicals in the atmosphere. We measured carbonyl compounds over urban Beijing, a megacity in the North China Plain, in summer and winter to investigate the relation of carbonyl compounds with haze and the interaction between carbonyl compounds and atmospheric radical cycling. We also determined carbonyl compounds in summer rainwater. Data of carbonyl compounds were analyzed in four cases, i.e., summer haze days (SHD), summer non-haze days (SND), winter haze days (WHD), and winter non-haze days (WND). Interestingly, the level of carbonyl compounds during WHD approached that of summer days. The results of the principal component analysis showed that there was no obvious source difference between SHD and SND. On WHD, however, more carbonyl compounds originated from the “diesel engine exhaust emission” than those on WND. We evaluated the effect of carbonyl compounds on the free radical cycling and the NO consumption potential for OH formation in the photochemical reactions using a novel ratio method. It was found that the production rate of ROx (the sum of OH, HO2 and RO2 radicals) was highest on SND, while the yield of ROx radicals from the reactions of carbonyl compounds was highest on WHD. Further, carbonyl compounds consumed more NO to produce OH radicals on WHD compared to the other three cases.

Heterogeneous reaction of peroxyacetic acid and hydrogen peroxide on ambient aerosol particles under dry and humid conditions: kinetics, mechanism and implications

Abstract. Hydrogen peroxide (H2O2) and organic peroxides play important roles in the cycle of oxidants and the formation of secondary aerosols in the atmosphere. Recent field observations have suggested that the budget of peroxyacetic acid (PAA, CH3C(O)OOH) is potentially related to the aerosol phase processes, especially to secondary aerosol formation. Here, we present the first laboratory measurements of the uptake coefficient of gaseous PAA and H2O2 onto ambient fine particulate matter (PM2.5) as a function of relative humidity (RH) at 298 K. The results show that the PM2.5, which was collected in an urban area, can take up PAA and H2O2 at the uptake coefficient (γ) of 10−4, and both γPAA and γH2O2 increase with increasing RH. The value of γPAA at 90 % RH is 5.4 ± 1.9 times that at 3 % RH, whereas γH2O2 at 90 % RH is 2.4 ± 0.5 times that at 3 % RH, which suggests that PAA is more sensitive to the RH variation than H2O2 is. Considering the larger Henry's law constant of H2O2 than that of PAA, the smaller RH sensitivity of the H2O2 uptake coefficient suggests that the enhanced uptake of peroxide compounds on PM2.5 under humid conditions is dominated by chemical processes rather than dissolution. Considering that mineral dust is one of the main components of PM2.5 in Beijing, we also determined the uptake coefficients of gaseous PAA and H2O2 on authentic Asian Dust storm (ADS) and Arizona Test Dust (ATD) particles. Compared to ambient PM2.5, ADS shows a similar γ value and RH dependence in its uptake coefficient for PAA and H2O2, while ATD gives a negative dependence on RH. The present study indicates that, in addition to the mineral dust in PM2.5, other components (e.g., soluble inorganic salts) are also important to the uptake of peroxide compounds. When the heterogeneous reaction of PAA on PM2.5 is considered, its atmospheric lifetime is estimated to be 3.0 h on haze days and 7.1 h on non-haze days, values that are in good agreement with the field observations.

Chemical characterization of size-resolved aerosols in four seasons and hazy days in the megacity Beijing of China

Size-resolved aerosol samples were collected by MOUDI in four seasons in 2007 in Beijing. The PM10 and PM1.8 mass concentrations were 166.0±120.5 and 91.6±69.7μg/m3, respectively, throughout the measurement, with seasonal variation: nearly two times higher in autumn than in summer and spring. Serious fine particle pollution occurred in winter with the PM1.8/PM10 ratio of 0.63, which was higher than other seasons. The size distribution of PM showed obvious seasonal and diurnal variation, with a smaller fine mode peak in spring and in the daytime. OM (organic matter=1.6×OC (organic carbon)) and SIA (secondary inorganic aerosol) were major components of fine particles, while OM, SIA and Ca2+ were major components in coarse particles. Moreover, secondary components, mainly SOA (secondary organic aerosol) and SIA, accounted for 46%–96% of each size bin in fine particles, which meant that secondary pollution existed all year. Sulfates and nitrates, primarily in the form of (NH4)2SO4, NH4NO3, CaSO4, Na2SO4 and K2SO4, calculated by the model ISORROPIA II, were major components of the solid phase in fine particles. The PM concentration and size distribution were similar in the four seasons on non-haze days, while large differences occurred on haze days, which indicated seasonal variation of PM concentration and size distribution were dominated by haze days. The SIA concentrations and fractions of nearly all size bins were higher on haze days than on non-haze days, which was attributed to heterogeneous aqueous reactions on haze days in the four seasons.

Variations in PM2.5, TSP, BC, and trace gases (NO2, SO2, and O3) between haze and non-haze episodes in winter over Xi'an, China

To investigate chemical profiles and formation mechanisms of aerosol particles in winter haze events, daily PM2.5 and TSP, 5-min BC, and 15-min trace gases (SO2, NO2, and O3) were measured continuously during Dec. 1–31, 2012 in Xi'an. Chemical analysis was also conducted for nine water-soluble inorganic ions (Na+, NH4+, K+, Mg2+, Ca2+, F−, Cl−, NO3−, and SO42−), organic carbon (OC), elemental carbon (EC), and eight carbon fractions (OC1, OC2, OC3, OC4, EC1, EC2, EC3, and OP) in both PM2.5 and TSP samples. Higher levels of TSP, PM2.5, BC, SO2, and NO2, and lower levels of O3 were observed during haze periods in comparison with non-haze days. The sum of the major secondary ionic species (NH4+, NO3−, and SO42−) in PM2.5 or TSP during haze periods was about 3 times of that during non-haze days. Ion balance calculations showed that PM2.5 samples were acidic during haze periods and were close to neutral during non-haze days. The mean carbon levels were 52.9 μg m−3 and 82.1 μg m−3 in PM2.5 and TSP, respectively, during haze events, which were ∼1.5 times of those during non-haze days. The diurnal variations of BC during non-haze days showed a bimodal distribution with two peaks coincided with traffic rush hours. This was not the case during haze periods, which exhibited a relatively smooth pattern but with high concentration levels, providing evidence of particle accumulation. The ratios of SO42−/EC, NO3−/EC, and NH4+/EC sharply increased during haze periods, indicating the important pathway of secondary inorganic species formation through aqueous-phase transformation under high relative humidity condition. This study also highlights that wintertime secondary organic carbon (SOC) formation can be an important contributor to carbonaceous aerosol, especially during haze periods.

Role of secondary aerosols in haze formation in summer in the Megacity Beijing

A field experiment from 18 August to 8 September 2006 in Beijing, China, was carried out. A hazy day was defined as visibility<l0km and RH (relative humidity)<90%. Four haze episodes, which accounted for ~60% of the time during the whole campaign, were characterized by increases of SNA (sulfate, nitrate, and ammonium) and SOA (secondary organic aerosol) concentrations. The average values with standard deviation of SO42−, NO3−, NH4+ and SOA were 49.8 (±31.6), 31.4 (±22.3), 25.8 (±16.6) and 8.9 (±4.1)μg/m3, respectively, during the haze episodes, which were 4.3, 3.4, 4.1, and 1.7 times those in the non-haze days. The SO42−, NO3−, NH4+, and SOA accounted for 15.8%, 8.8%, 7.3%, and 6.0% of the total mass concentration of PM10 during the non-haze days. The respective contributions of SNA species to PM10 rose to about 27.2%, 15.9%, and 13.9% during the haze days, while the contributions of SOA maintained the same level with a slight decrease to about 4.9%. The observed mass concentrations of SNA and SOA increased with the increase of PM10 mass concentration, however, the rate of increase of SNA was much faster than that of the SOA. The SOR (sulfur oxidation ratio) and NOR (nitrogen oxidation ratio) increased from non-haze days to hazy days, and increased with the increase of RH. High concentrations of aerosols and water vapor favored the conversion of SO2 to SO42− and NO2 to NO3−, which accelerated the accumulation of the aerosols and resulted in the formation of haze in Beijing.

Evolution of surface O3 and PM2.5 concentrations and their relationships with meteorological conditions over the last decade in Beijing

In this study, hourly and daily records since 2005 and correlation, regression and composite methods were used to analyze the long-term evolution of surface O3 and PM2.5 concentrations at the rural station of Shangdianzi (SDZ) and urban station of Baolian (BL) over Beijing and their relationships with meteorological conditions. The results show that the mean concentrations of PM2.5 (O3) decreased (increased) at the urban and rural stations over the last decade. The linear trends of the annual mean concentrations of PM2.5 at BL and SDZ were −31.8 ug/m3/10yr (−4.3%/yr) (p < 0.01) and −13.3 ug/m3/10yr (−2.9%/yr) (p < 0.05), respectively. In winter, the mean wind speed (Ws) and relative humidity (RH) were the most closely correlated with O3 at both stations, whereas RH and sunshine hours (S) were most closely correlated with PM2.5. The correlation coefficients and explained variances in spring and autumn were generally less than those in winter and greater than those in summer. Moreover, increase in precipitation can significantly reduce the PM2.5 concentration in both urban and rural areas in Beijing, whereas trace and light precipitation more effectively decreases the O3 concentration. Concentrations of PM2.5 (O3) on haze days increased by 114% (3%) and 162% (20%) compared with that on non-haze days at the urban and rural stations, respectively. This result suggests that haze is a major manifestation of air pollution in Beijing.

Chemical and optical properties of aerosols and their interrelationship in winter in the megacity Shanghai of China

A field campaign on air quality was carried out in Shanghai in winter of 2012. The concentrations of NO, NO2, NOx, SO2, CO, and PM2.5 increased during haze formation. The average masses of SO42−, NO3− and NH4+ were 10.3, 11.7 and 6.7μg/m3 during the haze episodes, which exceeded the average (9.2, 7.9, and 3.4μg/m3) of these components in the non-haze days. The mean values for the aerosol scattering coefficient (bsp), aerosol absorption coefficient (bap) and single scattering albedo (SSA) were 288.7, 27.7 and 0.91Mm-1, respectively. A bi-peak distribution was observed for the mass concentrations of CO, NO, NO2, and NOx. More sulfate was produced during daytime than that in the evening due to photochemical reactions. The mass concentration of NH4+ achieved a small peak at noontime. NO3− showed lower concentrations in the afternoon and higher concentrations in the early morning. There were obvious bi-peak diurnal patterns for bsp and bap as well as SSA. bsp and bap showed a positive correlation with PM2.5 mass concentration. (NH4)2SO4, NH4NO3, organic mass, elemental carbon and coarse mass accounted for 21.7%, 19.3%, 31.0%, 9.3% and 12.3% of the total extinction coefficient during non-haze days, and 25.6%, 24.3%, 30.1%, 8.1% and 8.2% during hazy days. Organic matter was the largest contributor to light extinction. The contribution proportions of ammonium sulfate and ammonium nitrate to light extinction were significantly higher during the hazy time than during the non-haze days.

Concentration and size distribution of viable bioaerosols during non-haze and haze days in Beijing.

Accumulation of airborne particulate matter (PM) has profoundly affected the atmospheric environment of Beijing, China. Although studies on health risks have increased, characterization of specific factors that contribute to increased health risks remains an area of needed exploration. Chemical composition studies on PM can readily be found in the literature but researches on biological composition are still limited. In this study, the concentration and size distribution of viable airborne bacteria and fungi were determined in the atmosphere from May to July 2013 in Beijing, China. Samples were collected during non-haze days and haze days based on the value of air quality index (AQI) PM2.5. Multiple linear regression results indicated that concentrations of viable bioaerosol exhibited a negative correlation with PM2.5 (AQI) ranging from 14 to 452. There was a little difference in size distribution of bioaerosol between non-haze and haze days that all airborne bacteria showed skewed trends toward larger sizes and airborne fungi followed a Gaussian distribution. Spearman's correlation analysis showed that a fraction of bioaerosol with fine and coarse particles had negative and positive relations with PM2.5 (AQI), respectively. Moreover, the temporal variation of d g (aerodynamic diameter) of bioaerosol with PM2.5 (AQI) fluctuated from 9:00 to 21:00, which suggested that their deposition pattern would vary during a day. The primary research in this study implied that aerodynamic size variation should be considered in assessing the bioaerosol exposure during haze weather.

Characteristics and formation mechanism of a winter haze–fog episode in Tianjin, China

Several heavy haze and fog episodes occurred in northern China in January of 2013. Data were collected and used to analyze the characteristics and mechanisms of formation of the haze–fog (HF) episode that occurred from January 10 to 12. The minimum hourly visibility was 112 m, as recorded on 12 January. The concentrations of particulate and gaseous pollutants increased continuously during this HF period. The concentration of PM2.5 increased faster than that of SO2 and NOx, and the rate of accumulation was greater at the beginning of the HF process than at other times. The average concentration of PM2.5, PM10, NOx, and SO2 on the HF days was 3.9, 3.6, 2.5, and 2.1 times higher than the values in the non-haze days. The scattering and absorption coefficients σsp and σap on the HF days were 4.0 and 4.3 times higher than the values in the non-HF days. The highest black carbon (BC) concentration was about 10 times higher than on the non-HF days. The concentrations of total carbon (TC), organic carbon (OC), and elemental carbon (EC) all increased, and the speed of the increase in OC was quicker than that of the EC. An increase in secondary inorganic pollutants (SO42−, NO3−) in PM2.5 was also observed. The concentrations of SO42− and NO3− on the HF days were 4 and 2 times those of the non-HF days. The increase in relative humidity on the HF days favored the formation of sulfate and nitrate during HF episode. Unfavorable meteorological conditions were the external cause of this HF episode. The southwest wind transported the pollutants from areas to the south of the study regions at the beginning of the HF episode. After the HF took shape, a strong descending air mass located in the high layer severely limited pollutant diffusion in the vertical direction. The strong temperature inversion and the weak horizontal wind limited the horizontal and vertical dispersion of pollutants. The high layer transport of the pollutants during the early period and the late accumulation of pollutants and the secondary formation of aerosols were important mechanisms for causing the formation of this HF episode.