Observational Insights into Isoprene Secondary Organic Aerosol Formation through the Epoxide Pathway at Three Urban Sites from Northern to Southern China.

Isoprene is the most abundant precursor of global secondary organic aerosol (SOA). The epoxide pathway plays a critical role in isoprene SOA (iSOA) formation, in which isoprene epoxydiols (IEPOX) and/or hydroxymethyl-methyl-α-lactone (HMML) can react with nucleophilic sulfate and water producing isoprene-derived organosulfates (iOSs) and oxygen-containing tracers (iOTs), respectively. This process is complicated and highly influenced by anthropogenic emissions, especially in the polluted urban atmospheres. In this study, we took a 1-year measurement of the paired iOSs and iOTs formed through the IEPOX and HMML pathways at the three urban sites from northern to southern China. The annual average concentrations of iSOA products at the three sites ranged from 14.6 to 36.5 ng m-3. We found that the nucleophilic-addition reaction of isoprene epoxides with water dominated over that with sulfate in the polluted urban air. A simple set of reaction rate constant could not fully describe iOS and iOT formation everywhere. We also found that the IEPOX pathway was dominant over the HMML pathway over urban regions. Using the kinetic data of IEPOX to estimate the reaction parameters of HMML will cause significant underestimation in the importance of HMML pathway. All these findings provide insights into iSOA formation over polluted areas.

The environmental benefit of Beijing-Tianjin-Hebei coal banning area for North China.

In order to achieve the targets specified in the Action Plan for Air Pollution Prevention and Control (APAPPC), a limited coal banning area (10,000 km2) was designated in the heavily polluted Beijing-Tianjin-Hebei region (BTH) for the first time in 2017. PM2.5 and elements were sampled by the network of BTH to evaluate the effectiveness of this policy. This study found that the fine days with PM2.5 < 75 µg m-3 accounted for 74.3% in the autumn and winter of 2017, which was significantly higher than that in 2016 (43%). The heavily polluted days (PM2.5 > 150 µg m-3) also decreased from 32.2% in 2016 to 4.9% in 2017. Arsenic (As) is an important tracer in coal consumption, which can be used to reflect the influence of the establishment of coal banning areas on north China. The cluster analysis of air mass forward trajectory identified that the number of polluted trajectories with PM2.5 and As in 2017 decreased by 47.6% and 49.7%, respectively. Under the implementation of the coal banning policy, the weighted concentration of PM2.5 and As decreased by 94.2 µg m-3 and 5.1 ng m-3 in the coal banning area, 60.9 µg m-3 and 3.4 ng m-3 in the no coal banning area in BTH, respectively. The influence of weighted concentration of PM2.5 and As in coal banning area on North China were 1.6-49.2 µg m-3 and 0.15-2.8 ng m-3, respectively, which was 38.8% and 29.7% lower than 2016. In coal banning area, BTH and other parts of North China, the reduction of the weight concentration of PM2.5 in 2017 accounted for 41.4%, 26.8% and 31.8% of the total reduction, respectively, so was the As in 39%, 26.3% and 34.6%, indicating that setting up a coal banning area scientifically in limited areas can produce remarkable regional benefit.

Concentrations and chemical compositions of PM10 during hazy and non-hazy days in Beijing.

In order to study the concentrations of major components, characteristics and comparison in hazy and non-hazy days of PM10 in Beijing, aerosol samples were collected at urban site in Beijing from December 29, 2014 to January 22, 2015. Heavy metals like Zn, Pb, Mn, Cu, As, V, Cr and Cd were deeply studied considering their toxic effects on human being; nine water-soluble inorganic ions (SO42-, NO3-, NH4+, Na+, K+, Cl-, Ca2+ and Mg2+) and carbon fractions (OC and EC) were also analyzed. The concentrations of heavy metals were 1.03-1.98 times higher in hazy days than those in non-hazy days, mainly due to biomass burning and coal burning. The trends in total heavy metals concentrations were basically consistent with the trends in PM concentrations except for two obvious periods (12.29-12.30; 1.14-1.15); but when air masses accumulated locally or around Beijing, trends in PM concentrations and heavy metals were opposite. The proportion for NO3-/SO42- indicated that mobile sources such as automobiles were important reasons for haze in Beijing. Correlation between OC and EC during non-hazy days was strong (R2 = 0.95) but it was low (R2 = 0.67) during hazy days, and large variations for OC/EC values occurred in hazy days. The calculated mass concentration of SOC is 2.58 µg/m3, which only accounted for 10.1% of the OC concentration. When air masses from the far north-west, they decreased PM concentration in Beijing and they were relatively clean; however, those from the near east, south-east and south of the mainland increased PM concentration and they were dirty.

Size-resolved water-soluble organic carbon and its significant contribution to aerosol liquid water.

Size-segregated aerosols collected in Beijing from 2021 to 2022 were used to investigate the contribution of organic aerosols to the aerosol liquid water content (ALWC), the influencing factors of ALWC, and the concentrations and size distribution characteristics of water-soluble organic carbon (WSOC) after clean air actions. The results showed that the concentration of WSOC in particulate matter (PM)1.8 was 3.52 ± 2.43 µg/m3 during the sampling period. Obvious changes were observed in the size distribution of WSOC after clean air actions, which may be attributed to the enhancement of atmospheric oxidation capacity and the decrease in PM concentration. The contribution of organic aerosols to the ALWC in fine PM was 18.1 % during the sampling period, which was more significant at lower particles concentration and smaller particle size ranges. The ambient relative humidity (RH) and the ratio of NO3-/SO42- had an apparent influence on ALWC. The continuous increase in the nitrate proportion significantly reduced the deliquescence point of the aerosols, making them prone to hygroscopic growth at lower RH. Analysis of the relation among nitrogen oxidation ratio (sulfur oxidation ratio), ALWC and PM1.8 mass concentrations suggests that organic matter has a significant effect on the formation of secondary inorganic aerosols in the initial phase of pollution formation and plays a crucial role in aerosol pollution formation in Beijing. These results are conducive to understanding the formation mechanism of aerosols and provide scientific data and theoretical support for the formulation of more effective emission-reduction measures.

Effects of the sea-land breeze on coastal ozone pollution in the Yangtze River Delta, China.

Aim at the effects of the coastal characteristic on ozone pollution in the Yangtze River Delta (YRD), a campaign was launched at the Ningbo, China in the summer of 2020, which mainly covered the monitoring of the vertical profiles of ozone (O3) concentration, three-dimensional wind field, temperature and humidity profiles and parameters of boundary layer dynamic-thermodynamic structure. At the coastal research station, a sea-land breeze (SLB) circulation accompanied by a concurrent coastal low-level jets (CLLJ) structure was observed and identified during 11-12 May 2020. The sea breeze first formed at 10:00 LT on 11 May, turned to land breeze at night, and returned to sea breeze again at 10:00 LT the next morning, prevailing at altitudes of 0-0.5 km and 0-0.3 km respectively. Land breeze at night carries O3 from the inland to the sea forming high ozone levels over the sea, and the shift of the sea breeze during daytime further blew pollution back to the land. Additionally, the conversion of SLB contributed to the occurrence of CLLJ at the altitudes of ~0.3-0.7 km by 02:00 and 06:00 LT, of which the center of wind speed reached ~13 m s-1. The CLLJ-induced turbulent activity decoupled the residual layer (RL) and stable boundary layer, leading to a reduction of RL-O3 levels and an increase of ~50 µg m-3 in surface-O3 concentration. The YRD's unique coastal characteristics make O3 pollution causes in coastal areas more complicated.

Mitigating NOX emissions does not help alleviate wintertime particulate pollution in Beijing-Tianjin-Hebei, China.

Stringent mitigation measures have reduced wintertime fine particulate matter (PM2.5) concentrations by 42.2% from 2013 to 2018 in the Beijing-Tianjin-Hebei (BTH) region, but severe PM pollution still frequently engulfs the region. The observed nitrate aerosols have not exhibited a significant decreasing trend and constituted a major fraction (about 20%) of the total PM2.5, although the surface-measured NO2 concentration has decreased by over 20%. The contributions of nitrogen oxides (NOX) emissions mitigation to the nitrate and PM2.5 concentrations and how to alleviate nitrate aerosols efficiently under the current situation still remains elusive. The WRF-Chem model simulations of a persistent and heavy PM pollution episode in January 2019 in the BTH reveal that NOX emissions mitigation does not help lower wintertime nitrate and PM2.5 concentrations under current conditions in the BTH. A 50% reduction in NOX emissions only decreases nitrate mass by 10.3% but increases PM2.5 concentrations by 3.2%, because the substantial O3 increase induced by NOX mitigation offsets the HNO3 loss and enhances sulfate and secondary organic aerosols formation. Our results are further consolidated by the occurrence of severe PM pollution in the BTH during the COVID-19 outbreak, with a significant reduction in NO2 concentration. Mitigation of NH3 emissions constitutes the priority measure to effectively lower the nitrate and PM2.5 concentrations in the BTH under current conditions, with 35.5% and 12.7% decrease, respectively, when NH3 emissions are reduced by 50%.

Evaluating the size distribution characteristics and sources of atmospheric trace elements at two mountain sites: comparison of the clean and polluted regions in China.

Size-resolved trace metal concentrations at two background sites were assessed during a 1-year observation campaign, with the measurements performed in parallel at two mountain sites, where Mt. Dinghu (DHS) located in the rural region of Pearl River Delta (PRD) and Mt. Gongga (GGS) located in the Tibetan Plateau region. In total, 15 selected trace elements (Mg, Al, K, V, Mn, Fe, Cu, Zn, As, Mo, Ag, Cd, Ba, Tl, and Pb) in aerosol samples were determined using inductively coupled plasma mass spectrometry (ICPMS). The major metals in these two mountain sites were Fe, K, Mg, and Ca with concentrations ranging between 241 and 1452 ng/m3, 428 and 1351 ng/m3, 334 and 875 ng/m3, and 376 and 870 ng/m3, respectively, while the trace metals with the lowest concentrations were Mo, Ag, Cd, and Tl with concentrations lower than 4 ng/m3 in DHS and 2 ng/m3 in GGS. The pronounced seasonal variability in the trace elements was observed in DHS, with lower concentrations in spring and summer and relatively high in winter and autumn, whereas seasonal variance of trace elements is hardly observed in Mt. Gongga. The size distribution pattern of crustal elements of Al, Mg, K, Ba, and Fe was quite similar in DHS and GGS, which were mainly found in coarse particles peaked at 4.7-5.8 µm. In addition, V, Mo, Ag, and Tl were also concentrated in coarse particles, although the high enrichment factor (EF > 100) of which suggested anthropogenic origin, whereas trace metals of Cd, Mn, Zn, As, Cu, and Pb concentrated in fine mode particles. Specifically, these trace metals peak at approximately 1.5 µm in DHS, while those in GGS peaked at diameter smaller than 0.3 µm, indicating the responsible for long-range transport from the far urban and industrialized areas. Multivariate receptor model combined with the enrichment factor results demonstrated that the trace elemental components at these two background sites were largely contributed from the fossil fuel combustion (55.4% in DHS and 44.0% in GGS) and industrial emissions factors (20.1% vs. 26.5%), which are associated with long distance transport from the coastal area of Southeast China and the Northwestern India, respectively, as suggested by the backward air mass trajectory analysis. Local sources from soil dust contributed a minor variance for trace elements in DHS (9.7%) and GGS (13.8%), respectively.

[Characterization and Size Distribution of Carbonaceous Aerosols at Mountain Dinghu].

To understand the characterization and sources of carbonaceous aerosols at Mountain Dinghu, organic carbon (OC) and elemental carbon (EC) in size-resolved aerosol samples were measured at a regional background site in South China using a DRI Model 2001A analyzer. The average mass concentrations of organic carbon (OC) are (5.6±2.0) µg ·m-3 in PM1.1, (7.3±2.4) µg ·m-3 in PM2.1, and (12.8±4.0) µg ·m-3 in PM9.0; the average mass concentrations of elemental carbon (EC) are (2.3±1.4) µg ·m-3in PM1.1, (2.7±1.6) µg ·m-3 in PM2.1, and (3.4±1.7) µg ·m-3 in PM9.0. OC concentrations in PM1.1 and PM2.1 account for 43.8% and 57.0% of OC in PM9.0, and EC concentrations in PM1.1 and PM2.1 account for 67.6% and 79.4%, respectively. OC and EC are enriched with fine particles. In PM1.1 and PM2.1, the highest concentrations of OC and EC are measured in autumn, and the lowest concentration of OC is measured in winter and EC in summer. In PM9.0, the highest OC concentration is measured in summer. Carbonaceous aerosols are mainly composed of OC2, EC1, OC3, and OC4. In summer, the concentration of OC3 is higher than that of EC1, suggesting that biogenic sources are dominant during summer. The concentration of EC1 in winter is the highest, indicating that the impacts of motor vehicle emissions are prominent in the local area during winter. OC and EC both show bimodal distributions in four seasons, with peaks in the size ranges of 0.43-0.65 µm for fine particles and 3.3-5.8 µm for coarse particles. In PM1.1 and PM2.1, the sources of OC are mainly primary emissions. In PM2.1, the highest concentration of SOC is measured in spring at (3.0±1.4) µg ·m-3 and the lowest in winter at (1.3±1.4) µg ·m-3, indicating that the secondary aerosol formation is significant in spring. At the Mountain Dinghu background site, OC is mainly from coal combustion and motor vehicle emissions for fine particles and from biogenic sources for coarse particles. EC is mainly from coal combustion, motor vehicle emissions, and dust.

Impact of the coal banning zone on visibility in the Beijing-Tianjin-Hebei region.

The Beijing-Tianjin-Hebei (BTH) region, which has the most severe air pollution in China, built a 10,000 km2 coal banning zone for pollution control in 2017. In this study, to evaluate the impact of banning coal zone on visibility (VIS), a chemical composition analysis, a chemical mass closure and the revised IMPROVE algorithm were applied to estimate the chemical components and lighting extinction coefficients (bext) of the fine particulate matter (PM2.5) collected at three urban sites (Beijing (BJ), Tianjin (TJ) and Shijiazhuang (SJZ)) and a regional background site (Xinglong (XL)) during autumn and winter of 2016-2017. Compared to measurements from 2016, the average PM2.5 from 2017 decreased by 44 µg m-3 (BJ), 37 µg m-3 (TJ), 69 µg m-3 (SJZ) and 10 µg m-3 (XL), respectively, accompanied by an improved VIS (3.2-4.6 km). The degradation of VIS caused by atmospheric aerosol is due to the light extinction. The bext clearly decreased by 58%, 51%, 56% and 54% at BJ, TJ, SJZ and XL, respectively. However, the reductions/improvements were more significant in winter than those in autumn, especially at BJ and TJ located in the coal banning zone. The decline (improvement) in PM2.5 (VIS) was 16%-37% (15%-27%) in autumn but 29%-60% (21%-83%) in winter. The reductions in SO42- (Cl-) in winter were 2.8 (3.2) and 7.4 (16.4) times larger than those in autumn at BJ and TJ, respectively. Reductions in ammonium sulfate, one of the main species of PM2.5 caused by coal burning, were particularly pronounced at three urban sites in winter (59%-68%). In addition, the reductions in bext in winter were 2.3 (BJ), 339.4 (TJ), 1.9 (SJZ) and 0.4 (XL) times larger than those in autumn. The results reveal that banning coal zone has a marked effect on controlling pollution in the BTH, especially in winter (scattering aerosol sulfate).

Characteristics of chemical composition and seasonal variations of PM2.5 in Shijiazhuang, China: Impact of primary emissions and secondary formation.

North China registers frequent air pollution episodes from high PM2.5 concentrations. Shijiazhuang is located at the intensive industrial zone of this region, but there is insufficient data on the chemical composition of PM2.5 and its sources in this city. In this study, the chemical and seasonal characteristics of PM2.5 in Shijiazhuang were investigated based on 12-h integrated PM2.5 measurements made over eight 1-month periods in each season between June 2014 and April 2016 (486 samples). The eight-season average concentration of PM2.5 was 138.8 µg m-3, and the major chemical components were secondary inorganic aerosol (SIA) species of sulfate, nitrate, and ammonium (41.5%), followed by organic matter (25.9%). The mass concentration and most of the chemical components of PM2.5 showed clear seasonal variation, with a winter-high and summer-low pattern. SO42- and NO3- were the dominant components at each pollution level in summer and autumn (18.1%-30.6% and 14.2%-27.0%, respectively). Sufficient gaseous oxidants (O3) concentrations and suitable meteorology conditions were observed in these two seasons. Highest SOR (0.61), SO42-/EC(10.8) and NOR (0.58), NO3-/EC (5.9) were found in summer and autumn, which indicated intense secondary transformation in these two seasons. Organic matter was the dominant species in winter, which increased from 17.1 µg m-3 for clean days (28.7% of PM2.5) to 169.1 µg m-3 (38.4% of PM2.5). The accumulation of primary emissions (coal combustion and biomass burning) was responsible for the increasing OM trend (especially for POC). The highest and leading proportion of mineral dust occurred in spring (20.3%-46.5%) as a result of higher wind speeds (up to 3 m/s). Potential source contribution function (PSCF) analyses implied that the border areas of Hebei, Henan and Shandong Provinces, together with the central area of Shanxi Province, contributed significantly to the PM2.5 pollution in Shijiazhuang, especially in autumn and winter.

[Mass Concentrations and Size Distributions of Water-soluble Inorganic Ions in Atmospheric Aerosols in Beibei District, Chongqing].

In order to study the concentration and distribution characteristics of water-soluble inorganic ions in aerosol particles of the Beibei district of Chongqing, aerosol samples were collected with an Andersen cascade impactor between March 2014 and February 2015. Water-soluble inorganic ions, including Na+, NH4+, K+, Mg2+, Ca2+, F-, Cl-, NO3-, and SO42- were determined for different particle sizes (9.00, 5.80, 4.70, 3.30, 2.10, 1.10, 0.65, and 0.43 µm) using the ion chromatography method. Results showed that SO42-, NH4+, NO3-, Cl-, Na+, and K+ were mainly distributed in fine particles, while Mg2+, Ca2+, and F- were mainly present in coarse particles. SNA (SO42-, NH4+, and NO3-) exhibited clear unimodal distribution, with peaks in the droplet mode of 0.65-1.10 µm, mainly present in the form of (NH4)2SO4 and NH4NO3 in fine particles. The formation of SO42- is mainly attributed to in-cloud processes and partly to oxidation of SO2. Na+, Cl-, and Mg2+ exhibited bimodal distribution in coarse and fine particles; K+ was a single peak distribution in the range of 0.43-1.10 µm, while peaks of F- and Ca2+ concentrations were in coarse particles. Average annual concentrations of total water-soluble ions in PM2.1 and PM9.0 were (32.68±15.28) µg·m-3and (48.01±19.66) µg·m-3 over the observation period. Seasonal variations of PM2.1 and PM9.0concentrations decreased in the order of winter > spring > summer > autumn. This was the same for most ions, but a small number of ions (F-, Mg2+ and Ca2+) had a different pattern in the spring, summer, and winter. The SNA were the major components of water-soluble ions in PM2.1, and Ca2+ was the major component of water-soluble ions in PM9.0 besides SNA. The concentration of cations was significantly higher than that of anions' in PM2.1 and PM9.0, with a certain correlation between different ions. Emissions from motor vehicle exhaust, combustion processes, soil sources, and fugitive dust were the major sources of water-soluble ions in this area. The effect of air temperature on secondary ions is significant (P<0.05), but relative humidity and wind speed have no significant effect (P>0.05).

Characterization and source identification of fine particulate matter in urban Beijing during the 2015 Spring Festival.

The Spring Festival (SF) is the most important holiday in China for family reunion and tourism. During the 2015 SF an intensive observation campaign of air quality was conducted to study the impact of the anthropogenic activities and the dynamic characteristics of the sources. During the study period, pollution episodes frequently occurred with 12days exceeding the Chinese Ambient Air Quality Standards for 24-h average PM2.5 (75µg/m3), even 8days with exceeding 150µg/m3. The daily maximum PM2.5 concentration reached 350µg/m3 while the hourly minimum visibility was <0.8km. Three pollution episodes were selected for detailed analysis including chemical characterization and diurnal variation of the PM2.5 and its chemical composition, and sources were identified using the Positive Matrix Factorization model. The first episode occurring before the SF was characterized by more formation of SO42- and NO3- and high crustal enrichment factors for Ag, As, Cd, Cu, Hg, Pb, Se and Zn and seven categories of pollution sources were identified, whereby vehicle emission contributed 38% to the PM2.5. The second episode occurring during the SF was affected heavily by large-scale firework emissions, which led to a significant increase in SO42-, Cl-, OC, K and Ba; these emissions were the largest contributor to the PM2.5 accounting for 36%. During the third episode occurring after the SF, SO42-, NO3-, NH4+ and OC were the major constituents of the PM2.5 and the secondary source was the dominant source with a contribution of 46%. The results provide a detailed understanding on the variation in occurrence, chemical composition and sources of the PM2.5 as well as of the gaseous pollutants affected by the change in anthropogenic activities in Beijing throughout the SF. They highlight the need for limiting the firework emissions during China's most important traditional festival.

[Pollution Characteristics of Organic Carbon and Elemental Carbon in Atmospheric Aerosols in Beibei District, Chongqing].

To study the pollution characteristics of atmospheric carbon aerosols, aerosol samples were collected via a cascade impactor (Andersen) from March 2014 to February 2015 in Beibei District, Chongqing. Organic carbon (OC) and element carbon (EC) were detected using a DRI 2001A carbon analyzer. The results showed that the annual average concentrations of OC and EC in PM2.1 were (16.3±7.6) and (1.8±0.7), respectively, and (25.0±9.6), and (3.2±1.3) µg·m-3, respectively, in PM9.0. The concentrations of both OC and EC were higher in winter and spring than in summer and autumn for PM2.1, whereas, for PM9.0, the concentration of OC was higher in summer and spring than in winter and autumn and that of EC was higher in winter and spring than in summer and autumn. The particle size distributions of OC and EC for the study year were analyzed, and it was found that those of OC were bimodal, with peaks in the size ranges of 0.43-0.65 µm for fine particles and 4.7-5.8 µm for coarse particles, and those of EC were trimodal, with peaks in the size ranges of 0.43-0.65 µm for fine particles and 4.7-5.8 µm for coarse particles and a concurrent significant peak in the particle size range of 2.1-3.3 µm. In addition, the correlations between OC and EC were analyzed and the SOC in PM2.1 was estimated. It was found that the average concentration of SOC was (6.3±5.9) µg·m-3, which accounted for 33.5%±22.6% of the OC concentration in Beibei District. Furthermore, OC and EC were significantly correlated. Finally, the pollution sources of atmospheric aerosols in Beibei were analyzed, and it was found that the pollution in Beibei mainly came from the exhaust gas of gasoline vehicles, biomass combustion, and coal combustion.

Size-resolved aerosol water-soluble ions during the summer and winter seasons in Beijing: Formation mechanisms of secondary inorganic aerosols.

Size-segregated water-soluble ionic species (WSIs) were measured using an Anderson cascade impactor from Jul. to Aug. 2008 and from Dec. 2009 to Feb. 2010 in urban Beijing. The results showed that fine particles (PM2.1, Dp < 2.1 µm) accounted for ∼49% (summer) and ∼34% (winter) of the total particulate mass, and WSIs accounted for 23-82% of the mass concentration of PM2.1. Secondary inorganic aerosols (SIAs, the sum of SO42-, NO3- and NH4+) accounted for more than 30% of the fine particles, which were greatly elevated during particle pollution events (PM events), thereby leading to an alteration of the size distributions of SO42- and NO3- to nearly single fine-mode distributions peaking at 0.65-2.1 µm. This finding suggests that heterogeneous aqueous reactions were enhanced at high RH values. SIAs also increased during dust events, particularly for coarse mode SO42-, which indicated enhanced heterogeneous reactions on the dust surface. The positive matrix factorization (PMF) model was used to resolve the bulk mass size distributions into condensation, droplet, and coarse modes, representing the three major sources of the particles. The formation of SO42- was attributed primarily to in-cloud or aerosol droplet processes during summer (45%), and the heterogeneous reaction of SO2 on mineral dust surfaces was an important formation pathway during winter (45%). The formation pathways of NO3- in fine particles were similar to those of SO42-, where over 30% were formed by in-cloud processes. This work provides important field measurement-based evidence for understanding the formation pathway of secondary inorganic aerosols in the megacity of Beijing.

[Characteristics of the Size Distribution of Water Soluble Inorganic Ions in Sanya, Hainan].

Size-resolved filter samples were collected in Sanya every other week from June 2012 to May 2014. The mass concentrations of water-soluble inorganic ions, including anions (Cl-, NO3-, SO42-) and cations (Na+, NH4+, K+, Mg2+, Ca2+) were measured by ion chromatography. The results showed that the total concentrations of measured water-soluble inorganic ions were (8.91±7.27) and (11.34±9.37) µg·m-3 in PM2.1 and PM2.1-9, respectively. In PM2.1, SO42- and NH4+ comprised 72.2% of all water-soluble inorganic ions, while in PM2.1~9, Cl-, Ca2+ and Na+ comprised 67.6% of all water-soluble inorganic ions. In PM2.1, the total concentrations of water-soluble inorganic ions had highest concentrations in winter and lowest concentrations in summer. In PM2.1~9, the total concentrations of water-soluble inorganic ions presented the highest concentrations in summer. SO42- and NH4+ showed bimodal size distributions and the peaks in the fine mode shifted from 0.43-0.65 µm in spring, summer and autumn to 0.65-1.1 µm in winter. NO3-, Na+, Cl-, Ca2+ and Mg2+ were unimodal with the peaks in the coarse mode of 4.7-9.0 µm. K+ showed bimodal size distribution with the fine mode at 0.43-0.65 µm and the coarse mode at 4.7-5.8 µm. PCA analysis showed that water-soluble inorganic ions were mainly affected by the secondary formation, sea salt and soil particles or falling dust.

Quantification of the impact of aerosol on broadband solar radiation in North China.

PM2.5 plays a key role in the solar radiation budget and air quality assessments, but observations and historical data are relatively rare for Beijing. Based on the synchronous monitoring of PM2.5 and broadband solar radiation (Rs), a logarithmic function was developed to describe the quantitative relationship between these parameters. This empirical parameterization was employed to calculate Rsn from PM2.5 with normalized mean bias (NMB) -0.09 and calculate PM2.5 concentration from Rsn with NMB -0.12. Our results indicate that this parameterization provides an efficient and straightforward method for estimating PM2.5 from Rs or Rs from PM2.5.

[Characteristics of Water-soluble Inorganic Ions in Atmospheric Aerosols in Shenyang].

To investigate the levels and seasonal variation of water soluble inorganic components in ambient aerosol in Shenyang, 25 samples were collected with Andersen cascade sampler from Jun. 2012 to May. 2013 and nine water-soluble ions in samples were analyzed by IC. The different characteristics of aerosols between clean and pollution days in winter were discussed based on these samples. The results showed that the annual concentrations of total water soluble inorganic ions were 22.30 µg·m-3 and 14.29 µg·m-3 in fine and coarse particles, and SO42- and Ca2+ were the most abundant ions, respectively. The ratio of mass concentration between SO42- and NO3- was 2.28 and the NH4+ existed in the form of (NH4)2SO4 and NH4NO3 in fine particles. The concentrations of total water soluble ions in fine particles were higher in winter and spring compared with those in summer and autumn, and they varied significantly between different seasons. The fossil fuel consumption led to the maximum values of secondary inorganic ions in fine particles during winter. The concentrations of total water soluble ions in coarse particles varied slightly though they were higher in autumn and lower in winter, and the wind-drifting sand was responsible for the higher concentration of Ca2+ in autumn in coarse particles. The concentration of SO42-, NO3-, NH4+ accounted for 80% of total water soluble inorganic ions during clean days and rose to 94% during pollution days. The ions were mostly concentrated in the size ranges of 0.43-0.65 µm and 0.43-2.1 µm respectively during clean and pollution days in fine mode. The peaks of SO42-, NO3-, NH4+ in fine mode shifted from 0.43-0.65 µm to 1.1-2.1 µm, which meant these ions were transformed from condensing mode to droplets mode during pollution days. The air mass produced at Lake Baikal and transported through high altitude to the sampling point caused clean days, however the air mass transported through industrial areas might bring pollutions to the sampling point then caused pollution days.

[Concentrations and Size Distributions of Water-soluble Inorganic Ions in Aerosol Particles in Taiyuan, Shanxi].

Size-resolved filter samples were collected in Taiyuan every other week from June 2012 to May 2014. The mass concentrations of water-soluble ions (Na+, NH4+, K+, Mg2+, Ca2+, F-, Cl-, NO3- and SO42-) were measured by ion chromatography. The results showed that the total concentrations of measured water-soluble ions were (15.39±9.91), (21.10±15.49) and (36.34±18.51) µg·m-3 in PM1.1, PM2.1 and PM9, respectively. In PM1.1 and PM2.1, secondary water-soluble ions (SO42-, NO3- and NH4+) comprised 87.59% and 86.30% of all water-soluble ions, respectively, while in PM9, SO42- and Ca2+ comprised 32.78% and 28.54% of all water-soluble ions, respectively. SO42- and NH4+ had higher concentrations in winter and summer, and lower in spring and autumn. NO3-, K+and Cl- presented similar seasonal variation with a descending order of winter >autumn >spring >summer, and Ca2+ and Mg2+ followed the sequence of spring >winter >autumn >summer. SO42- and NH4+ showed a unimodal size distribution and the peak in the fine mode shifted from 0.43-0.65 µm in spring and autumn to 0.65-1.1 µm in summer. NO3- showed a bimodal size distribution. NO3- and NH4+ were dominated by the fine mode peaking at 0.43-2.1 µm in winter, and NO3- was dominated by the coarse mode peaking at 4.7-5.8 µm in summer. K+, Na+and Cl- also showed a bimodal size distribution with the fine mode at 0.43-1.1 µm and the coarse mode at 4.7-5.8 µm. Ca2+, Mg2+ and F- were unimodal with the peak in the coarse mode of 4.7-5.8 µm. On heavily polluted days, the mass concentrations of secondary water-soluble ions and Cl- accumulated, and secondary water-soluble ions were unimodal with the peak in the fine mode of 1.1-2.1 µm. However, on clear days, secondary water-soluble ions showed a bimodal size distribution with the fine mode at 0.43-0.65 µm and the coarse mode at 4.7-5.8 µm. The peak of secondary water-soluble ions in the fine mode shifted. PCA analysis showed that the sources of water-soluble ions were dominated by the secondary formation, coal combustion, industrial emission, biomass burning, and soil particles or falling dust.

Spatial and seasonal variations of isoprene secondary organic aerosol in China: Significant impact of biomass burning during winter.

Isoprene is a substantial contributor to global secondary organic aerosol (SOA). The formation of isoprene SOA (SOAI) is highly influenced by anthropogenic emissions. Currently, there is rare information regarding SOAI in polluted regions. In this study, one-year concurrent observation of SOAI tracers was undertaken at 12 sites across China for the first time. The tracers formed from the HO2-channel exhibited higher concentrations at rural sites, while the tracer formed from the NO/NO2-channel showed higher levels at urban sites. 3-Methyltetrahydrofuran-3,4-diols exhibited linear correlations with their ring-opening products, C5-alkenetriols. And the slopes were steeper in the southern China than the northern China, indicating stronger ring-opening reactions there. The correlation analysis of SOAI tracers with the factor determining biogenic emission and the tracer of biomass burning (levoglucosan) implied that the high level of SOAI during summer was controlled by biogenic emission, while the unexpected increase of SOAI during winter was largely due to the elevated biomass burning emission. The estimated secondary organic carbon from isoprene (SOCI) exhibited the highest levels in Southwest China. The significant correlations of SOCI between paired sites implied the regional impact of SOAI in China. Our findings implicate that isoprene origins and SOAI formation are distinctive in polluted regions.

[Characteristics of the Size Distribution of Water Soluble Inorganic Ions During a Typical Haze Pollution in the Autumn in Shijiazhuang].

To characterize the size distribution of water soluble inorganic ions (WSⅡ) in haze days, particle samples were collected by an Andersen cascade impactor in Shijiazhuang from October 15 to November 14 in 2013, and the concentrations of eight kinds of WSⅡ (Na+, NH4+, K+, Mg2+, Ca2+, Cl-, NO3-and SO42-) during a typical haze episode were analyzed by ion chromatography. Sources and formation mechanism of WSⅡ were analyzed based on their size distributions. The results showed that Shijiazhuang suffers serious air pollution during the autumn season. The daily average concentrations of PM10and PM2.5were (361.2±138.7) µg·m-3 and (175.6±87.2) µg·m-3 and the daily average concentration of PM2.5was 2.3 times as high as the national secondary standard. The total water soluble inorganic ion concentrations (TWSⅡ) in clean days, light haze days and heavy haze days were(64.4±4.6)µg·m-3, (109.9±22.0)µg·m-3 and (212.9±50.1) µg·m-3 respectively. In addition, the ratio of secondary inorganic ions (SNA:SO42-, NO3- and NH4+) in TWSⅡ increased from 44.9% to 77.6% as changed from clean days to the heavy haze days, suggesting the evolution of haze episodes mainly originated from the formation and accumulation of SNA. The size distributions of SO42-, NO3- and NH4+ were bimodal in clean days, peaking at 0.43 -0.65 µm and 4.7-5.8 µm, respectively, which changed to unimodal distribution in both the light and heavy haze days, peaking at 0.65-1.1 µm. Owing to high humidity during the heavy haze days, the aqueous phase reactions of SO42- and NO3- were likely promoted, which led to the transformation of condensation mode in clean days to the droplet mode in haze days. The size distributions of Na+, Mg2+ and Ca2+ were different with that of SNA, which showed a coarse mode peaking at 4.7-5.8 µm both in clean and haze days, whereas K+and Cl- showed a bimodal distribution both in clean and haze days, although the modal size was different in clean and haze days.