Observation-based sources evolution of non-methane hydrocarbons (NMHCs) in a megacity of China.

Both concentrations and emissions of many air pollutants have been decreasing due to implement of control measures in China, in contrast to the fact that an increase in emissions of non-methane hydrocarbons (NMHCs) has been reported. This study employed seven years continuous NMHCs measurements and the related activities data of Shanghai, a megacity in China, to explore evolution of emissions and effectiveness of air pollution control measures. The mixing ratio of NMHCs showed no statistical interannual changes, of which their compositions exhibited marked changes. This resulted in a decreasing trend of ozone formation potential by 3.8%/year (p < 0.05, the same below), which should be beneficial to ozone pollution mitigation as its production in Shanghai is in the NMHCs-limited regime. Observed alkanes, aromatics and acetylene changed by +3.7%/year, -5.9%/year and -7.4%/year, respectively, and alkenes showed no apparent trend. NMHCs sources were apportioned by a positive matrix factorization model. Accordingly, vehicular emissions (-5.9%/year) and petrochemical industry emissions (-7.1%/year) decreased significantly, but the decrease slowed down; significant reduction in solvent usage (-9.0%/year) appeared after 2010; however, emissions of natural gas (+12.6%/year) and fuel evaporation (with an increasing fraction) became more important. The inconsistency between observations and inventories was found in interannual trend and speciation as well as source contributions, emphasizing the need for further validation in NMHCs emission inventory. Our study confirms the effectiveness of measures targeting mobile and centralized emissions from industrial sources and reveals a need focusing on fugitive emissions, which provided new insights into future air policies in polluted region.

Fog-Haze Transition and Drivers in the Coastal Region of the Yangtze River Delta.

Low-visibility events (LVEs) are severe weather phenomena that are closely linked with anthropogenic pollution, which negatively affects traffic, air quality, human health, and the environment. This study conducted a two-month (from October to December 2019) continuous measurement campaign on Chongming Island in Shanghai to characterize the LVEs transition and its drivers. The LVEs accounted for 38% of the time during the campaign, of which mist accounted for 14%, fog-haze for 13%, haze for 6%, and fog for 5%. The fog and mist mainly occurred from midnight to early morning, while haze mostly occurred during the daytime. Different LVEs were interdependent and transitioned from one to another. Fog generally turned into haze after sunrise, while haze turned into fog after sunset. Their formation and evolution were caused by the combined impacts of meteorological conditions and aerosol particles. It was found that temperature difference was the dominant meteorological factor driving the evolution of LVEs. Within the short term, cooling led to a greater increase in relative humidity than humidification. Radiative cooling during the night promoted the formation of fog and mist. During fog and mist events, cloud condensation nuclei (CCN) were mainly internally mixed due to the impact of fog droplet removal and aqueous/heterogeneous aerosol reactions occurring under high humidity. Increased CCN concentration appeared to increase the fog droplet number and liquid water content in fog events. Overall, conditions of high humidity and high particle loading were conducive to LVEs, whereas conditions of sufficient water vapor at a low particle level and sufficient particles at a low humidity level also caused LVEs. This study provided insights into LVEs classification, evolution scheme, and aerosol roles from a micro point of view. The findings could be useful for improving forecasts of local radiative fog and other LVEs.

Effects of shipping emissions on cloud physical properties over coastal areas near Shanghai.

To investigate the effects of shipping aerosols on radiation, cloud physical properties, and near-surface PM2.5, four sensitive experiments with the WRF-Chem model were performed over coastal areas near Shanghai for July 2014. In general, the direct effect of shipping aerosols resulted in negative shortwave (SW) radiation forcing at the land surface. However, when considering the indirect effect, the downward SW radiation at the sea surface declined significantly. By the direct effect, shipping aerosols could modify cloud structure, resulting in a higher cloud base, lower cloud top, and shallower cloud depth. With the indirect effect included, both the cloud base and cloud top showed a declining trend over sea areas. The indirect effect of shipping aerosols was relatively more significant in influencing clouds. For example, the results revealed a 1.2% change of low cloud coverage from the indirect effect but only a 0.1% change due to the direct effect. Through their direct and indirect effects, shipping aerosols cause non-negligible impacts on precipitation, which are concentrated within light precipitation (<0.1 mm h-1). Finally, we concluded that after considering the shipping aerosols, the peak of the cloud droplet spectrum increases by about 50 cm-3/µm. It can be found that when the average volume radius of the cloud droplet is less than 2 µm, the number concentration of cloud droplets increases sharply, and when the average radius of the cloud drop is greater than 2 µm and less than 5 µm, the cloud droplet number concentration drops sharply.

Spatial distribution and sources of winter black carbon and brown carbon in six Chinese megacities.

The light-absorbing carbonaceous aerosols, including black carbon (BC) and brown carbon (BrC), influenced heavily on aerosol environmental quality and the Earth's radiation. Here, a winter campaign to characterize BC and BrC in PM2.5 was conducted simultaneously in six Chinese megacities (i.e., Harbin, Beijing, Xi'an, Shanghai, Wuhan, and Guangzhou) using continual aethalometers. The combinations of advanced aethalometer and generalized additive model (GAM) were used to precisely quantify the BC and BrC sources in these megacities. The averaged light-absorbing coefficients of BC (babs-BC) and BrC (babs-BrC) were 28.6 and 21.8 Mm-1 in northern cities, they were 1.4 and 2.7 times higher than those in southern cities. The BrC dominated the total babs (>40%) in northern cities but low to 20% in southern cities. On the other hand, the BC fractions were high in the southern cities, with the contributions of 62.4-79.7%, whereas much lower values of 53.7-59.4% in the northern cities. Source apportionment showed that the combustion of liquid fuels (e.g., gasoline or diesel) was highly dominant to babs-BC (>80%) in Guangzhou and Wuhan. This was further supported by the high NO2 loadings in the GAM model. Solid fuels (i.e., biomass or coal) contributed a substantial portion to total babs-BC in the other four cities where the high abundances of primary babs-BrC were observed. The diurnal trend showed the peaks of secondary-BrC (babs-BrCS) and babs-BrCS/ΔCO in the northern cities occurred at high relative humidity in nighttime, implying the secondary BrC formation was possibly related to aqueous reactions in winter. In contrast, in the southern cities of Shanghai and Guangzhou, the accumulation of vehicle emissions during the morning traffic rush hours lead the formation of secondary BrC through photochemical reactions. The results of this work can be applied for the development of more effective practices to control BC and BrC on regional scale.

Spatiotemporal changes of surface solar radiation: Implication for air pollution and rice yield in East China.

The changes of surface solar radiation (SSR) have significant implication for air pollution and rice yield. In this study, gridded SSR data, derived from multi-platform datasets and radiation model, were used to analyze its spatiotemporal changes over East China during 2000-2016. The results show SSR experiences dimming during 2000-2005, then turns into brightening till 2016. Both aerosol optical depth (AOD) and single scattering albedo (SSA) contribute to SSR trend. AOD dominates the spatiotemporal changes of SSR in East China, and this impact is higher in the North than the South. SSA has little impact on SSR with low AOD, but its contribution to SSR becomes important as AOD increases. Moreover, gridded planet boundary layer (PBL) was simulated by the Weather Research and Forecasting Model (WRF) and SSR-PBL relationship was also explored. Long-term evidence indicates PBL has a regulatory effect on SSR in the air pollution. Additionally, aerosol-induced radiation reduction can influence rice yield in East China, and it can result in about mean 6.74% reduction in rice yield over East China. Province-level changes of aerosol-induced reduction in rice production were also evaluated and it suggests the impact of aerosols on rice production is non-negligible, especially in Jiangsu and Anhui Province. Our study underscores the importance of aerosol pollution on surface radiation and the mitigation of aerosols is beneficial for crop production under climate change.

Inorganic composition and occult deposition of frost collected under severe polluted area in winter in the North China Plain.

Frost as a kind of deposition plays an important role in the removal of atmospheric compounds. However, studies concerning frost in the atmospheric environment were rare although chemical composition in frost samples might be affected by the surrounding atmospheric environment. In this study, a total of 35 frost samples were collected by means of a homemade glass-plate frost condenser under severe polluted condition in the North China Plain (NCP) from Dec. 4, 2018 to Mar. 2, 2019. The pH values and water-soluble ions (WSI) were conducted. The extremely high concentrations of WSI were found, which reflected the severe pollution significantly affecting the level of chemical composition in frost. The major ions were Ca2+, SO42- and HCO3- with averaged concentrations of 1242, 1143, 1076 µeq L-1, respectively. These ions were at least one order of magnitude higher than the previous frost studies. HCO3- was one of the most abundant components in frost. Its high proportion contributed to the ionic balance and led to the alkaline characteristic of frost. SO42- had the almost doubled ratio in frost compared with the concurrent PM2.5 samples. Different from the huge diversity of chemical components in PM2.5, the frost had similar ratio of WSI under great variety of PM2.5 concentrations. It proved that PM2.5 had less effect on the ratio of WSI in frost. Nutrient ions of NH4+, NO3- and K+ accounted for 13.9%, 5.4% and 1.6% of the total averaged concentrations, respectively. On average, per square meter soil would receive 563 µg nitrogen and 123 µg potassium nutrient during a frost night. High occult deposition flux of ions indicated the strong scavenging effect from the frost event. In addition, the occult deposition flux of SO42- was comparable to the dry deposition flux, further emphasizing frost process as a non-negligible atmospheric removal pathway of SO42-.

Size distribution and chemical composition of primary particles emitted during open biomass burning processes: Impacts on cloud condensation nuclei activation.

As a major source of fine particles, open biomass burning can affect climate and the hydrological cycle via the formation of cloud condensation nuclei (CCN) and their deposition. This study investigated the effect of aerosol size and chemical composition (water-soluble compounds, elemental carbon, and organic carbon) on CCN activation during the complete combustion of six commonly used crop (rice, wheat, corn, soybean, and cotton) and leaf residues in a simulation chamber developed for this study. Geometric mean diameters (GMD) of emitted primary particles ranged from 68 to 130 nm and water-soluble compound (WSC) content ranged from 33 to 50%. Although GMDs and WSCs possessed similar temporal tendencies during the combustion process, their average values were dependent on the type of biomass. Number concentration ratios of CCN and particle (CCN/CN) ranged from 1.4-2.1% and 5.8-8.3% at supersaturations of 0.2% and 1.0%, respectively. The CCN/CN value increased during the combustion process when the GMD and WSC content increased. Correlation coefficients for GMD and CCN activation ranged from 0.62 to 0.93, while correlations for WSC and CCN activation ranged from 0.33 to 0.95. Soybean biomass had the highest correlations for both GMD and WSC with CCN activation at various supersaturations. These results suggest that the size and chemical composition of biomass aerosols are important in CCN formation, while the aerosol size has a higher impact.

Size-resolved particle oxidative potential in the office, laboratory, and home: Evidence for the importance of water-soluble transition metals.

Particulate matter (PM) oxidative potential (OP) is an emerging health metric, but studies examining the OP of indoor PM are rare. This paper focuses on the relationships between respiratory exposure to OP and PM water-soluble composition in indoor environments. Size-resolved PM samples were collected between November 2015 and June 2016 from an office, home (including bedroom, living room, and storeroom), and laboratory using a MOUDI sampler. Particles from each source were segregated into eleven size bins, and the water-soluble metal content and dithiothreitol (DTT) loss rate were measured in each PM extract. The water-soluble OP (OPws) of indoor PM was highest in the office and lowest in the home, varying by factors of up to 1.2; these variations were attributed to differences in occupation density, occupant activity, and ventilation. In addition, the particulate Cu, Mn, and Fe concentrations were closely correlated with OPws in indoor particles; the transition metals may have acted as catalysts during oxidation processes, inducing ·OH formation through the concomitant consumption of DTT. The OPws particle size distributions featured single modes with peaks between 0.18 and 3.2 µm across all indoor sites, reflecting the dominant contribution of PM3.2 to total PM levels and the enhanced oxidative activity of the PM3.2 compared to PM>3.2. Lung-deposition model calculations indicated that PM3.2 dominated the pulmonary deposition of the OPws (>75%) due to both the high levels of metals content and the high deposition efficiency in the alveolar region. Therefore, because OPws has been directly linked to various health effects, special attention should be given to PM3.2.

Impact of adsorbed nitrate on the heterogeneous conversion of SO2 on α-Fe2O3 in the absence and presence of simulated solar irradiation.

Adsorbed nitrate is ubiquitous in the atmosphere, and it can undergo photolysis to produce oxidizing active radicals. Nitrate photolysis may be coupled with the oxidation conversions of atmospheric gaseous pollutants. However, the processes involved remain poorly understood. In this study, the impact of adsorbed nitrate on the heterogeneous oxidation of SO2 on α-Fe2O3 was investigated in the absence and presence of simulated solar irradiation by using in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). The results indicate that for α-Fe2O3 particles with no adsorbed nitrate, the formation of adsorbed sulfate on humid particles is stronger than that on dry particles. Meanwhile, light can also promote the heterogeneous conversion of SO2 and the formation of sulfate on dry particles because α-Fe2O3 is a typical photocatalyst. However, the heterogeneous conversion of SO2 on humid α-Fe2O3 particles is somewhat suppressed under light, suggesting the occurrence of photoinduced reductive dissolution. For the heterogeneous conversion of SO2 on α-Fe2O3 particles with adsorbed nitrate, the formation of sulfate on humid particles is still higher than that on dry particles. For the dry α-Fe2O3 particles with adsorbed nitrate, light promotes the formation of adsorbed sulfate. For the humid α-Fe2O3 particles with adsorbed nitrate, the heterogeneous conversion of SO2 under light is stronger than that under no light, indicating that the photolysis of adsorbed nitrate is coupled with the oxidation of SO2 and the formation of sulfate. The consumption of adsorbed nitrate and the formation of adsorbed N2O4 are observed during the introduction of SO2. A possible mechanism for the impact of adsorbed nitrate on the heterogeneous conversion of SO2 on α-Fe2O3 particles is proposed, and atmospheric implications based on these results are discussed.

Association of short-term exposure to ambient air pollutants with exhaled nitric oxide in hospitalized patients with respiratory-system diseases.

BACKGROUND: Previous studies have suggested that exposure to ambient air pollutants may adversely affect human health. However, few studies have examined the health effects of exposure to ambient air pollutants in hospitalized patients. OBJECTIVES: To evaluate the association between short-term exposure to ambient air pollutants and exhaled nitric oxide fraction (FeNO) in a large cohort of hospitalized patients. METHODS: FeNO was detected for 2986 hospitalized patients (ages 18-88 years). Daily average concentrations of SO2, NO2, O3, CO, PM2.5 and PM10 in 2014 and 2015 were obtained from nine fixed-site monitoring stations. Multiple linear regression models were chosen to assess the associations of exposure to ambient air pollutants with FeNO while adjusting for confounding variables. Lagged variable models were selected to determine the association between FeNO and ambient air pollutants concentrations with lags of up to 7 days prior to FeNO testing. RESULTS: Interquartile-range (IQR) increases in the daily average SO2 (8.00 µg/m3) and PM2.5 (37.0 µg/m3) were strongly associated with increases in FeNO, with increases of 3.41% [95% confidence interval (CI), 0.94-5.93%] and 2.72% (95%CI, -0.09% to 5.61%), respectively. However, FeNO levels were not statistically associated with PM10, NO2, O3 or CO. In the two-pollutant models, the maximum correlation was for ambient SO2. We also found that FeNO was associated with IQR increases in daily average ambient concentrations of SO2 up to 3 and 4 days after the exposure events. CONCLUSIONS: Short-term exposure to SO2 and PM2.5 were positively correlated with FeNO levels in hospitalized patients in Shanghai.

Long-term variation of satellite-based PM2.5 and influence factors over East China.

With the explosive economic development of China over the past few decades, air pollution has attracted increasing global concern. Using satellite-based PM2.5 data from 2000 to 2015, we found that the available emissions of atmospheric compositions show similar yearly variation trends to PM2.5, even if the synchronization is not met for each composition, implying that the intensity of anthropogenic emissions dominates the temporal variation of PM2.5 in East China. Empirical orthogonal function analysis demonstrates that the dominant variability in the seasonal PM2.5 is closely associated with climate circulation transformation, incarnated as the specific climate index such as the Asia Polar Vortex intensity in spring, the Northern Hemisphere Subtropical High Ridge Position for the leading mode and the Kuroshio Current SST for the second mode in summer, the Asia Polar Vortex Area for the leading mode and the Pacific Polar Vortex Intensity for the second mode in autumn, the NINO A SSTA for the leading mode and the Pacific Decadal Oscillation for the second mode in winter. Therefore, apart from anthropogenic emissions effects, our results also provide robust evidence that over the past 16 years the climate factor has played a significant role in modulating PM2.5 in eastern China.

Influence of pollutants on activity of aerosol cloud condensation nuclei (CCN) during pollution and post-rain periods in Guangzhou, southern China.

Atmospheric pollutions have an important impact on aerosol, condensation nuclei (CN) and cloud condensation nuclei (CCN) loadings near the ground through disturbing particle size, number, chemical composition and reactions, mixing state, hygroscopicity, and so on. Aerosols and CCN were measured in urban Guangzhou during pollution and post-rain periods to examine effects of particulate pollutants on aerosol CCN activity and compare their mechanisms between summer and winter. In contrast with different levels of pollutions, particle matter (PM2.5) and number (CN) and CCN almost showed an opposite trend to aerosol activity (CCN/CN). In summer, new particle formation (NPF) events triggered by photochemical reactions (e.g. O3) always occurred in no-pollution daytime, and increased significantly CN and CCN as a dominant contributor to secondary aerosols. Under pollution conditions, the gas-to-particle transition driven by photochemical reactions guided the formation and aging processes of particles in daytime, especially in changing soluble species, whereas atmospheric oxidation and heterogeneous reactions dominated at night. In winter, stagnant weather conditions, high pollutant levels and relatively high RH were in favor of particle growing and aging through enhancing secondary particle formation and heterogeneous reactions. The wet scavenging of precipitation reduced greatly CCN amount by scouring pre-existing particles in winter, and during post-rain period the photochemical reactions did not promote the burst of secondary particle formation in the absence of ozone, compared with summer. The results may provide insights into the relationship between aerosol moisture absorption and pollution that may be useful for improving air quality.

Trends in heterogeneous aqueous reaction in continuous haze episodes in suburban Shanghai: An in-depth case study.

Heterogeneous aqueous reaction plays important roles in the enhanced formation of secondary aerosols during haze. However, its occurrence in haze episodes remains poorly understood. In this study, the trends in heterogeneous aqueous reaction in continuous haze episodes were investigated by an in-depth case analysis. The highly time-resolved measurements of water-soluble inorganic ions of PM2.5 were conducted in a suburban of Shanghai, China, and continuous haze episodes, which occurred from Feb. 18 to Feb. 28, were selected as studied cases. Results showed that fine particle pollution in Baoshan was serious. High concentrations of secondary inorganic aerosol ions and the higher sulfur oxidation ratio (SOR) and nitrogen oxidation ratio (NOR) on haze days indicated enhanced conversions from SO2 and NOx to their corresponding particulate phases. The high-nitrate haze episode and the high-sulfate haze episode were identified. Further simulations revealed that the PM2.5 particles had strong acidity during the high-nitrate and high-sulfate haze episodes whether they were calculated by E-AIM 4 or by ISORROPIA II. It was found that particulate liquid water was more sensitive to nitrate than sulfate, and played significant roles in the heterogeneous aqueous reactions of NO2 and secondary nitrate formation during haze episodes, especially in the high-sulfate haze episode. Further analysis indicated that the high-nitrate haze episode favoured the occurrence of heterogeneous aqueous phase oxidation of SO2, and the more water was in the particles, the more SO2 was converted to sulfate aerosols. This work provides an important field measurement-based evidence for understanding the important contributions of the heterogeneous aqueous reactions to secondary aerosol pollution and the tendencies of heterogeneous aqueous reactions in the formation of secondary sulfate and nitrate aerosols in suburban Shanghai.

Particle Size Distributions of Oxidative Potential of Lung-Deposited Particles: Assessing Contributions from Quinones and Water-Soluble Metals.

Redox-active species in ambient particulate matter (PM) cause adverse health effects through the production of reactive oxygen species (ROS) in the human respiratory tract. However, respiratory deposition of these species and their relative contributions to oxidative potential (OP) have not been described. Size-segregated aerosols were collected during haze and nonhaze periods using a micro-orifice uniform deposit impactor sampler at an urban site in Shanghai to address this issue. Samples were analyzed for redox-active species content and PM OP. The average dithiothreitol (DTT) activity of haze samples was approximately 2.4-fold higher than that of nonhaze samples and significantly correlated with quinone and water-soluble metal concentrations. The size-specific distribution data revealed that both water-soluble OPvDTT (volume-normalized OP quantified by DTT assay) and OPmDTT (mass-normalized OP) were unimodal, peaking at 0.56-1 and 0.1-0.32 µm, respectively, due to contributions from accumulation-mode quinones and water-soluble metals. We further estimated that transition metals (mainly copper and manganese) contributed 55 ± 13% of the DTT activity while quinones accounted for only 8 ± 3%. Multiple-path particle dosimetry calculations estimated that OP deposition in the pulmonary region was mainly from accumulation-mode transition metals despite quinones having the highest DTT activity. This behavior is primarily attributed to the efficiency of deposition of transition metals in the pulmonary region being approximately 1.2-fold greater than that of quinones. These results reveal that accumulation-mode transition metals are significant contributors to the OP of deposited water-soluble particles in the pulmonary region of the lung.

Long-term characteristics of satellite-based PM2.5 over East China.

With the explosive economic development of China over the past few decades, air pollution has become a serious environmental problem and has attracted increasing global concern. Using satellite-based PM2.5 data from 2000 to 2015, we found that the temporal-spatial variation of PM2.5 in East China is characterized by high concentrations in the northern part and low concentrations in the southern part of East China, and by being seasonally high in autumn and winter but low in spring and summer. We also found that the regional average PM2.5 concentration shows an approximative peak pattern over the last 16years, with the highest, 60.13µgm-3, and the lowest, 46.18µgm-3, occurring in 2007 and 2000, respectively. Despite obviously diminishing heavy polluted regions with a PM2.5 of >80µgm-3 after 2011, those cells dominated by natural background have still not recovered back to the clean level of 2000. These characteristics are valuable information to analyze the relative contributions of anthropogenic emissions and atmospheric conditions to the temporal-spatial variation characteristics of PM2.5.

Particle size distribution and respiratory deposition estimates of airborne perfluoroalkyl acids during the haze period in the megacity of Shanghai.

This study presents the particle size distribution and respiratory deposition estimates of airborne perfluoroalkyl acids (PFAAs) during the haze period. Size-segregated haze aerosols were collected from an urban location in Shanghai using an eight-stage air sampler. The samples were analyzed for eight PFAAs using ultra-high-performance liquid chromatography tandem triple quadrupole mass spectrometry. The quantification results showed that the concentrations of particle-bound Σ 8PFAAs ranged from 0.26 to 1.90 ng m-3 (mean: 1.44 ng m-3). All of the measured PFAAs particle size distributions had a bimodal mode that peaked respectively in accumulation size range (0.4 < Dp < 2.1 µm) and coarse size ranges (Dp > 2.1 µm), but the width of each distribution somewhat varied by compound. The emission source, molecular weight, and volatility of the PFAAs were important factors influencing the size distribution of particle-bound PFAAs. Of these compounds, PFUnDA presented a strong accumulation in the fine size range (average 75% associated with particles <2.1 µm), followed by PFOA (69%) and PFDA (64%). The human risk assessment of PFOS via inhalation was addressed and followed the same pattern as the size distribution, with a 2-fold higher risk for the fine particle fraction compared to the coarse particle fraction at urban sites. Approximately 30.3-82.0% of PFAA deposition (∑PFAA: 72.5%) in the alveolar region was associated with particles <2.1 µm, although the contribution of fine particles to the total PFAAs concentration in urban air was only 28-57% (∑8PFAAs: 48%). These results suggested that fine particles are significant contributors to the deposition of PFAAs in the alveolar region of the lung.

Comparison of aerosol and cloud condensation nuclei between wet and dry seasons in Guangzhou, southern China.

Cloud condensation nuclei (CCN), condensation nuclei (CN) and aerosol chemical composition were measured simultaneously at an urban site of Guangzhou from July to August 2015 and in January 2016, and the seasonal variations of aerosol activated fractions (NCCN/NCN) as well as their relevant influence factors were further studied accordingly. NCN is generally higher in winter (dry season), whereas NCCN and NCCN/NCN are mostly higher in summer (wet season) instead. In particular, NCCN and NCCN/NCN are much lower at smaller supersaturation levels (SS<0.2) in winter. In spite of similar diurnal variations for NCCN and NCN, NCCN/NCN indicates an opposite tendency, relatively lower at midday, dusk and before midnight. Other than the size of particles as well as their chemical composition, some other factors, such as mass, gas precursors, pollutant transportation, meteorological conditions, etc., also contribute to the variations of NCCN and NCCN/NCN. Particles from the local source or local-oceanic combination source cast influence on CN and CCN significantly, while the pollutants originating from and crossing over distant polluted areas contribute largely to CCN/CN. NCN and NCCN are relatively higher under pollution-free conditions in summertime and polluted conditions in wintertime, but NCCN/NCN is just the opposite. On various polluted conditions, aerosol CCN activities are greatly discrepant between summer and winter, especially during mist or heavy haze periods. The results imply that anthropogenic pollutants exert critical impacts on aerosol CCN activation.

Atmospheric size-resolved trace elements in a city affected by non-ferrous metal smelting: Indications of respiratory deposition and health risk.

This study examines size-resolved heavy metal data for particles sampled near an urban site affected by non-ferrous metal smelting in China with a focus on how particle sizes impact regional respiratory deposition behavior. Particles with aerodynamic diameters between 0.43 and 9 µm were collected during winter haze episodes from December 2011 to January 2012. The results showed that concentrations of individual trace elements ranged from ∼10-2-∼104 ng/m3. Mass size distributions exhibit that Cu, Zn, As, Se, Ag, Cd, TI, and Pb have unimodal peak in fine particles range (<2.1 µm); Al, Ti, Fe, Sr, Cr, Co, Ni, Mo, and U have unimodal peak in coarse range (>2.1 µm), and Be, Na, Mg, Ca, Ba, Th, V, Mn, Sn, Sb, and K have bimodal profiles with a dominant peak in the fine range and a smaller peak in the coarse range. The total deposition fluxes of trace elements were estimated at 2.1 × 10-2 - 4.1 × 103 ng/h by the MPPD model, and the region with the highest contribution was the head region (42% ± 13%), followed by the tracheobronchial region (11% ± 3%) and pulmonary region (6% ± 1%). The daily intake of individual element for humans occurs via three main exposure pathways: ingestion (2.3 × 10-4 mg/kg/day), dermal contact (2.3 × 10-5 mg/kg/day), and inhalation (9.0 × 10-6 mg/kg/day). A further health risk assessment revealed that the risk values for humans were all above the guidelines of the hazard quotient (1) and cancer risk (10-6), indicating that there are potential non-cancer effects and cancer risks in this area.

Long-range and regional transported size-resolved atmospheric aerosols during summertime in urban Shanghai.

In this study, the concentrations of water soluble ions (WSI), organic carbon (OC), and elemental carbon (EC) of size-resolved (0.056-18µm) atmospheric aerosols were measured in July and August 2015 in Shanghai, China. Backward trajectory model and potential source contribution function (PSCF) model were used to identify the potential source distributions of size-resolved particles and PM1.8-associated atmospheric inorganic and carbonaceous aerosols. The results showed that the average mass concentrations of PM0.1, PM1, and PM1.8 were 21.21, 82.90, and 100.1µgm-3 in July and 7.00, 29.21, and 35.10µgm-3 in August, respectively, indicating that the particulate matter pollution was more serious in July than in August in this study due to the strong dependence of the aerosol species on the air mass origins. The trajectory cluster analysis revealed that the air masses originated from heavily industrialized areas including the Pearl River Delta (PRD) region, the Yangtze River Delta (YRD) region and the Beijing-Tianjin region were characterised with high OC and SO42- loadings. The results of PSCF showed that the pollution in July was mainly influenced by long-range transport while it was mainly associated to local and intra-regional transport in August. Besides the contributions of anthropogenic sources from YRD and PRD region, ship emissions from the East China Sea also made a great contribution to the high loadings of PM1.8 and PM1.8-associated NO3-, NH4+, and EC in July. SO42- in Shanghai was dominantly ascribed to anthropogenic sources and the high PSCF values for PM1.8-associated SO42- observed in August was mainly due to the ship emissions of Shanghai port, such as Wusong port and Yangshan deep-water port. These results indicated that the particulate pollutants from long-range transported air masses and shipping made a significant contribution to Shanghai's air pollution.

Seasonal contributions to size-resolved n-alkanes (C8-C40) in the Shanghai atmosphere from regional anthropogenic activities and terrestrial plant waxes.

Size-resolved aerosol samples from the Shanghai atmosphere were analyzed for normal alkanes (n-alkanes, C8-C40) by comprehensive two-dimensional gas chromatography-flame ionization detection and gas chromatography-triple quadruple mass spectroscopy to study their size distribution and contributions from potential regional sources based on a one-year (2012-2013) sampling campaign. The n-alkane concentrations ranged from 62.3 to 398.5ngm-3, with an annual average of 227.6ngm-3. Particle-associated n-alkanes exhibited a bimodal distribution with one peak in the accumulation-mode size range and the other in the coarse-mode size range. As the carbon number increased, the peak in the accumulation mode intensified and the peak in the coarse mode weakened, in accordance with variation of their corresponding volatilities. Source indices (carbon preference index, average chain length, odd-even carbon number preference, unresolved to resolved n-alkanes ratio, and plant wax n-alkanes ratio) indicated that the n-alkane source profile shifted from an anthropogenic-dominated pattern in winter and spring to a terrestrial plant wax-influenced pattern in summer and autumn. Further trajectory cluster analysis and potential source contribution function modeling showed that anthropogenic activities were mainly in the North China Plain and East China and that terrestrial plant waxes originated in Anhui, Zhejiang, and Jiangxi Provinces. The results of our study provide useful information for evaluating the influence of anthropogenic and biogenic activities on the atmospheric transport of important secondary organic aerosol precursors to megacities in East Asia.