Formation Mechanism Of Haze Research Articles

Key role of atmospheric water content in the formation of regional haze in southern China

To elucidate the formation mechanism of haze and the important role of atmospheric humidity in haze formation, comprehensive observations were carried out at regional sites in the Pearl River Delta region of southern China from October 22 to November 6, 2014. Meteorological parameters, chemical compositions, aerosol secondary conversions and aerosol radiative forcing were analyzed. A lower wind speed (WS) and planetary boundary layer (PBL) can inhibit the horizontal and vertical diffusion of pollutants, leading to the accumulation of pollutant concentrations. A higher atmospheric relative humidity (RH) can promote aerosol secondary conversions, leading to an increase in secondary aerosol concentrations. Aerosol scattering hygroscopic growth properties and aerosol single scattering albedo (SSA) also increase with increasing RH, resulting in an increase in aerosol radiative forcing and a decrease in the PBL height, aggravating the formation of meteorological conditions that are not conducive to the dilution of pollutants. Conversely, a higher aerosol concentration also increases aerosol radiative forcing, forming a positive feedback loop. When the RH decreases and the WS increases, the loop enters a negative feedback process to reduce pollutant concentration.

Characteristics and formation mechanisms of winter haze in Changzhou, a highly polluted industrial city in the Yangtze River Delta, China

Changzhou, an industrial city in the Yangtze River Delta, has been experiencing serious haze pollution, particularly in winter. However, studies pertaining to the haze in Changzhou are very limited, which makes it difficult to understand the characteristics and formation of winter haze in this area, and develop effective control measures. In this study, we carried out continuous online observation of particulate matter, chemical components, and meteorology in Changzhou in February 2017. Our results showed that haze pollution occurred frequently in Changzhou winter and exhibited two patterns: dry haze with low relative humidity (RH) and wet haze with high RH. Water-soluble inorganic ions (SO42−, NO3−, and NH4+) accounted for ∼52.2% of the PM2.5 mass, of which sulfate was dominant in wet haze periods while nitrate was dominant in other periods. With the deterioration of haze pollution, the proportion of nitrate in PM2.5 increased, while sulfate proportion increased under wet haze and decreased under dry haze. Dry haze and wet haze appeared under slow north wind and south wind, respectively, and strong north wind or sea breeze scavenged pollution. We found that formation of nitrate occurred rapidly in daytime with high concentrations of odd oxygen (Ox = O3 + NO2), whereas formation of sulfate occurred rapidly during nighttime with high RH, indicating that photochemistry and heterogeneous reaction were the major formation mechanisms for nitrate and sulfate, respectively. Through the cluster analysis of 36-h backward trajectories, five sources of air masses from three directions were identified. High PM2.5 concentrations (84.1 μg m−3 on average) usually occurred under the influence of two clusters (46%) from the northwest, indicating that regional transport from northern China aggravated the winter haze pollution in Changzhou. Emission reduction, particularly the mobile sources, and regional joint prevention and control can help to mitigate the winter haze in Changzhou.

Severe haze in northern China: A synergy of anthropogenic emissions and atmospheric processes

Regional severe haze represents an enormous environmental problem in China, influencing air quality, human health, ecosystem, weather, and climate. These extremes are characterized by exceedingly high concentrations of fine particulate matter (smaller than 2.5 µm, or PM2.5) and occur with extensive temporal (on a daily, weekly, to monthly timescale) and spatial (over a million square kilometers) coverage. Although significant advances have been made in field measurements, model simulations, and laboratory experiments for fine PM over recent years, the causes for severe haze formation have not yet to be systematically/comprehensively evaluated. This review provides a synthetic synopsis of recent advances in understanding the fundamental mechanisms of severe haze formation in northern China, focusing on emission sources, chemical formation and transformation, and meteorological and climatic conditions. In particular, we highlight the synergetic effects from the interactions between anthropogenic emissions and atmospheric processes. Current challenges and future research directions to improve the understanding of severe haze pollution as well as plausible regulatory implications on a scientific basis are also discussed.

Profile of Zhisheng An

Zhisheng An of the Institute of Earth Environment of the Chinese Academy of Sciences (CAS) is a leader in the multidisciplinary field of Earth system science. His integration of Quaternary geology and global change methodologies beginning in the 1980s marked a paradigm shift and continues to facilitate climate change research. With geologist and mentor Tungsheng Liu, An pioneered studies concerning the climate significance of China’s loess sediments. He has conducted formative research on the history, dynamics, and environmental effects of Asian monsoons. Elected as a foreign associate of the National Academy of Sciences in 2016, An synthesizes recent advances in the fundamental mechanisms of severe haze formation in Northern China in his Inaugural Article (1). The synthesis could inform future regulatory policies to mitigate China’s haze-associated problems. Zhisheng An. Image courtesy of Zhang Yi (Chinese Academy of Sciences, Xi’an, China). An was raised in Nanjing, China by parents who were both teachers. An says, “My father Mengzhou An helped to nurture my writing skills, sense of logic, and philosophical thinking.” An attended a high school affiliated to Nanjing Normal University, where he developed an appreciation for science and the liberal arts. Inspired by a talk given by Nanjing University chemist Anbang Dai, An envisioned his future as a scientist. An planned to focus on physics, but in 1958 received an admission notice from the newly established Nanjing Geology College, which was later incorporated into Nanjing University’s geology department. His mother Zhihua Jiao urged him to attend the college, and An followed her advice. His interest in geology and nature grew during college-sponsored field trips. After earning a bachelor’s degree in geology in 1962, An attended the CAS Institute of Geology and the CAS Institute of Geochemistry for postgraduate studies in Quaternary geology. An’s supervisor Liu introduced him to research on …

Modeling and efficient quantified risk assessment of haze causation system in China related to vehicle emissions with uncertainty consideration

Urban haze has become a severe pollution problem in China. Vehicle emission may be a key factor leading to haze pollution in China's megacities due to the rapid growth of vehicles and corresponding energy consumption. Until now, the haze formation mechanisms in China remain highly uncertain, which have not yet been understood quantitatively. In this work, an efficient modified haze causation system related to vehicle emissions is developed for reliable quantified risk assessment of urban haze in China's megacities. And fuzzy mathematical theory combining with fault tree approach is investigated and employed as the analysis tool/strategy. To provide objective basis for the reliability and practicability of the quantitative assessment results, an efficient data extraction strategy and relevant mathematical models are proposed and developed for the probability determination of basic risk events. Besides, the probability uncertainty of basic risk events during the data extraction is taken into account, where the occurrence probability of basic events is described as triangular fuzzy number, the quantitative analysis results will be more reliable and more tally with the actual situation. After the haze causation system related to vehicle emissions is established along with the identification of all critical risk factors related to vehicle emissions, Beijing and Tianjin are taken as illustrated case studies for the quantified risk assessment of haze causation system related to vehicle emissions in China. All the analysis results demonstrated that this work may provide a useful and effective tool/strategy for efficient quantified risk assessment and risk management of haze causation system relate to vehicle emission in China.

Size-fractionated water-soluble ions during autumn and winter: Insights into volatile ammonium formation mechanisms in Shanghai, a megacity of China

Abstract Size-fractionated aerosols were collected by a Micro-Orifice Uniform Deposit Impactor at an urban site in Shanghai during the autumn and winter of 2014. The results showed that the average concentration of PM1.8 increased from 49 μg m−3 in autumn to 74 μg m−3 in winter. By contrast, the relative contribution of the water-soluble inorganic species decreased from 40% in autumn to 31% in winter. This finding suggests that the increase of organic matter (OM) greatly contributed to the deterioration of particle pollution in winter. Compared to autumn, the concentration of sulfate decreased whereas the concentration of NH4Cl increased significantly and became an important constituent of the fine particles in winter. The formation of nitrate in autumn became significant at [NH4+]/[SO42−] > 2, indicating that H2SO4 was fully neutralized by NH3 to form (NH4)2SO4. Our results showed that the regression between [NO3−]/[SO42−] and [NH4+]/[SO42−] drawn an unrealistic nitrate formation mechanism when the particulate NH4Cl was abundant. Replacing [NO3−] with {[NO3−]+[Cl−]} in the regression between [NO3−]/[SO42−] and [NH4+]/[SO42−], it is established that (NH4)2SO4 is preferentially formed before the excess available NH3 can react with HNO3 and HCl to form NH4NO3 and NH4Cl during wintertime. The concentrations of particulate sulfate and nitrate were not positively correlated with the ambient relative humidity, indicating that heterogeneous reactions on wet particles were not the key to haze formation in Shanghai during winter. Our results suggest that more studies are needed to understand the complex haze formation mechanisms in China.

Heavy Particulate Matter Pollution during the 2014-2015 Winter in Tianjin, China

Tianjin, a city located in North China, is heavily polluted with frequent haze, particularly in winter. In this study, continuous online field observations of the sulfate, nitrate, ammonium, PM2.5, and gaseous pollutant concentrations in addition to the meteorological parameters were conducted in Tianjin during the 2014–2015 winter (December–January–February). The PM2.5 concentrations ranged from 5.6 to 495.6 µg m–3, with an average value of 112.2 ± 96.1 µg m–3. The worst pollution was observed in January, when levels on 10% of the days exceeded 250 µg m–3, qualifying as severely polluted, and four haze episodes, each lasting 5–7 days, occurred in rapid succession (separated by ~1-day intervals). Back-trajectory and chemical composition analysis suggested that elevated levels of secondary ionic aerosol species were a primary cause of these episodes. Regional transport of PM2.5 also played a large role in the formation of haze. CO was selected as an inactive chemical tracer in studying the chemical process of PM2.5 formation. The results indicated that when high concentrations of PM2.5 were present, the formation of secondary PM2.5 increased while the photochemical production of O3 ceased. The sulfur oxidation ratio [SOR = nSO42–/(nSO42– + nSO2); n refers to the molar concentration] and nitrate oxidation ratio [NOR = nNO3–/(nNO3– + nNO2)] increased with the PM2.5 level, and heterogeneous processes on the surfaces of fine particles rather than photochemistry drove the haze events. This research elucidates haze formation mechanisms, which must be understood in order to create effective control policies in Tianjin.

Review on formation mechanism analysis method and control strategy of urban haze in China

Abstract Due to the rapid urbanization and industrialization, and excessive consumption of fossil fuel, haze weather characterized by PM2.5 has become a severe pollution problem in major Chinese cities recently, which has harmful effect on the air quality, visibility, clime system and human health. To indicate suitable directions for the prevention and control of haze pollution, the pollutant source apportionment and formation mechanism of urban haze should be figured out firstly. In this work, we briefly review the frequently-used methods for PM2.5 source apportionment and formation mechanism analysis of urban haze based on normal perspective in recent years. Furthermore, based on the new perspective of systematic methodology, the utilization of fault tree approach for the causation mechanism analysis of urban haze is significantly introduced and discussed. Finally, the recent progress on controlling strategies of urban haze in China is also synoptically introduced and discussed. It is expected that more effective tool/method can be found, developed and employed for the causation mechanism analysis and risk management of urban haze in China.

Physicochemical analysis of individual atmospheric fine particles based on effective surface-enhanced Raman spectroscopy

Fine particles associated with haze pollution threaten the health of more than 400 million people in China. It is therefore of great importance to thoroughly investigate and understand their composition. To determine the physicochemical properties in atmospheric fine particles at the micrometer level, we described a sensitive and feasible surface-enhanced Raman scattering (SERS) method using Ag foil as a substrate. This novel method enhanced the Raman signal intensities up to 10,000 a.u. for ν(NO3−) in fine particles. The SERS effect of Ag foil was further studied experimentally and theoretically and found to have an enhancement factor of the order of ~104. Size-fractionated real particle samples with aerodynamic diameters of 0.4–2.5 μm were successfully collected on a heavy haze day, allowing ready observation of morphology and identification of chemical components, such as soot, nitrates, and sulfates. These results suggest that the Ag-foil-based SERS technique can be effectively used to determine the microscopic characteristics of individual fine particles, which will help to understand haze formation mechanisms and formulate governance policies.

Vertical Distribution Characteristics of PM2.5 Observed by a Mobile Vehicle Lidar in Tianjin, China in 2016

We present mobile vehicle lidar observations in Tianjin, China during the spring, summer, and winter of 2016. Mobile observations were carried out along the city border road of Tianjin to obtain the vertical distribution characteristics of PM2.5. Hygroscopic growth was not considered since relative humidity was less than 60% during the observation experiments. PM2.5 profile was obtained with the linear regression equation between the particle extinction coefficient and PM2.5 mass concentration. In spring, the vertical distribution of PM2.5 exhibited a hierarchical structure. In addition to a layer of particles that gathered near the ground, a portion of particles floated at 0.6–2.5-km height. In summer and winter, the fine particles basically gathered below 1 km near the ground. In spring and summer, the concentration of fine particles in the south was higher than that in the north because of the influence of south wind. In winter, the distribution of fine particles was opposite to that measured during spring and summer. High concentrations of PM2.5 were observed in the rural areas of North Tianjin with a maximum of 350 μg m–3 on 13 December 2016. It is shown that industrial and ship emissions in spring and summer and coal combustion in winter were the major sources of fine particles that polluted Tianjin. The results provide insights into the mechanisms of haze formation and the effects of meteorological conditions during haze–fog pollution episodes in the Tianjin area.

A Theoretical Approach for Understanding the Haze Phenomenon in Bottled White Wines at Molecular Level

The stabilisation of the proteinaceous material in the wine matrix represents one of the big challenges for the production of quality white wines, but the characterisation of the mechanism that governs the interactions between its components is still a very challenging goal. The aim of this study was to provide new information for developing new technologies in the stabilisation of bottled white wines using a novel theoretical approach. This method combines electronic structure calculations for the determination of the a stable conformation of three ligands that may interact with one of the proteins responsible for the haze in wines, the thaumatin-like protein (TLP), with the search for the mode of binding between this protein and its ligands through docking calculations. The result shows that sites that exposed positive residues to the surface of the protein are the sites favoured for the caffeic acid (CA) binding. Additionally, it was observed that the ligand with the lowest binding energy (-7.38 kcal/mol) was the quercetin (Q). The presence of a π-π stacking interaction with the residue F118 is confirmed in a family of TLP-Q complexes, and it is proposed that the mechanism of haze formation in white wines during bottle storage seems to be related to the interaction of polyphenolic molecules with some residues of this big cavity; these residues or sites of interaction can be considered as future targets in the control of the haze phenomena and in the research on alternatives to the fining treatment in the wine industry.

Smoke haze over the European part of Russia in the summer of 2016: A link to wildfires in Siberia and atmospheric circulation anomalies

The mechanism of smoke haze formation over the European part of Russia (EPR) in the summer of 2016 is analyzed using satellite measurements, ground-based observations, reanalysis data, and trajectory modeling. The analysis reveals that smoke in the atmosphere over EPR with the aerosol optical depth increase up to 3 was caused by the long-range transport of combustion products from Siberian wildfires. The increase in the concentration of smoke aerosol in the atmosphere over EPR was accompanied by the increase in the concentration of carbon monoxide in the air. The long-range atmospheric transport of the products of pyrogenic emission from east to west for a distance up to 5000 km with the speed of 5–6 m/s predominantly occurred in the lower troposphere. The peculiarities of tropospheric circutation over Northern Eurasia in July 2016 are identified which were responsible for the transport of combustion products in the troposphere for thousands of kilometers in the direction opposite to the westerlies that prevail in the mid-latitudes.

Characteristics and source apportionment of PM2.5 during persistent extreme haze events in Chengdu, southwest China

Based on detailed data from Chengdu Plain (CP) from 6 January to 16 January, two typical haze episodes were analyzed to clarify the haze formation mechanism in winter. Weather conditions, chemical compositions, secondary pollutant transformation, optical properties of aerosols, the potential source contribution function (PSCF) and source apportionment were studied. The planetary boundary layer (PBL) height decreased distinctly during the haze episodes and restrained air pollutant vertical dispersion. As the haze worsened, the value of PBL × PM2.5 increased notably. The [NO3−]/[SO42−] ratio was 0.61, 0.76 and 0.88 during a non-haze period, episode 1 and episode 2, respectively, indicating that the mobile source of the air pollution is increasingly predominant in Chengdu. Water vapor also played a vital role in the formation of haze by accelerating the chemical transformation of secondary pollutants, leading to the hygroscopic growth of aerosols. The PSCF and backward trajectories of the air masses indicated that the pollution mainly came from the south. The secondary inorganic aerosols, vehicle emissions, coal combustion, biomass burning, industry, and dust contributed 34.1%, 24.1%, 12.7%, 12.3%, 7.6%, and 7.2% to PM2.5 masses in episode 1 and 28.9%, 23.1%, 9.4%, 9.5%, 20.3% and 7.5% in episode 2.

Insight into winter haze formation mechanisms based on aerosol hygroscopicity and effective density measurements

Abstract. We characterize a representative particulate matter (PM) episode that occurred in Shanghai during winter 2014. Particle size distribution, hygroscopicity, effective density, and single particle mass spectrometry were determined online, along with offline analysis of water-soluble inorganic ions. The mass ratio of SNA ∕ PM1. 0 (sulfate, nitrate, and ammonium) fluctuated slightly around 0.28, suggesting that both secondary inorganic compounds and carbonaceous aerosols contributed substantially to the haze formation, regardless of pollution level. Nitrate was the most abundant ionic species during hazy periods, indicating that NOx contributed more to haze formation in Shanghai than did SO2. During the representative PM episode, the calculated PM was always consistent with the measured PM1. 0, indicating that the enhanced pollution level was attributable to the elevated number of larger particles. The number fraction of the near-hydrophobic group increased as the PM episode developed, indicating the accumulation of local emissions. Three banana-shaped particle evolutions were consistent with the rapid increase of PM1. 0 mass loading, indicating that the rapid size growth by the condensation of condensable materials was responsible for the severe haze formation. Both hygroscopicity and effective density of the particles increased considerably with growing particle size during the banana-shaped evolutions, indicating that the secondary transformation of NOx and SO2 was one of the most important contributors to the particle growth. Our results suggest that the accumulation of gas-phase and particulate pollutants under stagnant meteorological conditions and subsequent rapid particle growth by secondary processes were primarily responsible for the haze pollution in Shanghai during wintertime.

Characterization of size-resolved urban haze particles collected in summer and winter at Taiyuan City, China using quantitative electron probe X-ray microanalysis

The aim of the study is to characterize the size-resolved urban haze particles and investigate their modification in morphology and composition in summer and winter using the semi-quantitative electron probe X-ray microanalysis (EPMA) based on both scanning and transmission electron microscopies equipped with ultrathin-window energy dispersive X-ray spectrometers (SEM-EDX and TEM-EDX). The haze and non-haze particles were collected through a seven-stage May cascade impactor on Dec. 29–30, 2009 and Jan. 8–9 and July 11–14, 2010 in Taiyuan, a typical inland city in the North China Plain. Approximately 3752 atmospheric particles in the size ranges of 4–2μm, 2–1μm, 1–0.5μm, and 0.5–0.25μm in aerodynamic diameter were measured and identified according to their secondary electron or TEM images and elemental atomic concentrations calculated through a Monte Carlo simulation program. Results show that on the haze days many reacted or aged mineral dust particles were encountered, in which the sulfate-containing ones outnumbered the nitrate-containing ones in the winter samples while it was on the contrary in the summer samples, suggesting different haze formation and evolution mechanisms in summer and winter. Furthermore, in the haze events (especially in summer), many CNOS-rich particles, likely mixtures of water-soluble organic carbon with (NH4)2SO4 or NH4HSO4, were observed not only in the submicron but also in the super-micron fractions. The simultaneous observation of the fresh and aged CNOS-rich particles in the same SEM or TEM images implied that the status and components of secondary particles were complicated and changeable. The significant increase of both elemental concentration ratios of [N]/[S] and [C]/[S] in the aged ones compared to the fresh ones indicated that NH4NO3 and secondary organic matter were likely absorbed onto (NH4)2SO4 or NH4HSO4 particles and mixed with them. K-rich, Fe-rich, and heavy metal-containing particles in TEM-EDX measurement were detected more in the winter haze samples than in the summer ones, suggesting that they tend to be smaller in size and mainly derive from anthropogenic biomass burning and coal combustion. It was concluded that the combined use of SEM-EDX and TEM-EDX can identify both submicron and super-micron urban haze particles in a straightforward way and trace their modifications in size, shape, mixing state, and chemical compositions in different seasons, helping address their evolution processes and hazards on human health.

欧亚波列与京津冀雾霾的关系及形成机制

利用NCEP/NCAR再分析资料和京津冀雾霾资料，采用聚类分析等统计方法对京津冀雾霾异常年环流场进行了分类，发现导致1月京津冀雾霾异常的欧亚大陆500 hPa环流场主要是两个模态的波列分布，方差贡献为0.9。重点讨论了两个模态欧亚波列分布及对应京津冀雾霾异常的形成机制，表明极地近地面层的温度特征决定了中高纬度大气的环流特征。当极区气温偏低时，极涡偏强，欧亚大陆形成东-西向“正、负、正”距平波列，京津冀雾霾天气偏多；反之，则偏少。当格陵兰海到巴伦支海区域气温偏高时，欧亚大陆为西北—东南向“正、负、正”距平波列，京津冀雾霾天气偏多；反之，则偏少。 Based on the NCEP/NCAR Reanalysis data and the haze data of Beijing-Tianjin-Hebei (BTH) re-gion, the circulation of haze abnormal years over the Beijing-Tianjin-Hebei region is classified by cluster analysis and other statistical methods. The results show that two mainly modes of wave trains distribution over Eurasia at 500 hPa circulation field will result in haze abnormal of Beijing-Tianjin-Hebei region in January. Their variance contribution reaches 0.9. This study fo-cuses on two modes of Eurasian wave trains distribution and the formation mechanism of haze over the Beijing-Tianjin-Hebei region; it shows that the characteristics of the polar atmospheric surface layer temperature determine that of the mid-high latitude atmosphere circulation. When the polar surface layer temperature is on the low side, the polar vortex is strong, there will be a “+ − +” anomaly distribution from west to east over the Eurasian continent, the haze weather over the Beijing-Tianjin-Hebei region will be more, and vice versa; When the temperature from the Greenland Sea to the Barents Sea region is on the high side, there will be a “+ − +” anomaly distribution from northwest to southeast over the Eurasian continent, the haze weather over the Beijing-Tianjin-Hebei region will be more, and vice versa.

Characteristics of aerosol pollution during heavy haze events in Suzhou, China

Abstract. Extremely severe haze weather events occurred in many cities in China, especially in the east part of the country, in January 2013. Comprehensive measurements including hourly concentrations of PM2.5 and its major chemical components (water-soluble inorganic ions, organic carbon (OC), and elemental carbon (EC)) and related gas-phase precursors were conducted via an online monitoring system in Suzhou, a medium-sized city in Jiangsu province, just east of Shanghai. PM2.5 (particulate matter with an aerodynamic diameter of 2.5 µm or less) frequently exceeded 150 µg m−3 on hazy days, with the maximum reaching 324 µg m−3 on 14 January 2013. Unfavorable weather conditions (high relative humidity (RH), and low rainfall, wind speed, and atmospheric pressure) were conducive to haze formation. High concentrations of secondary aerosol species (including SO42−, NO3−, NH4+, and SOC) and gaseous precursors were observed during the first two haze events, while elevated primary carbonaceous species emissions were found during the third haze period, pointing to different haze formation mechanisms. Organic matter (OM), (NH4)2SO4, and NH4NO3 were found to be the major contributors to visibility impairment. High concentrations of sulfate and nitrate might be explained by homogeneous gas-phase reactions under low RH conditions and by heterogeneous processes under relatively high RH conditions. Analysis of air mass trajectory clustering and potential source contribution function showed that aerosol pollution in the studied areas was mainly caused by local activities and surrounding sources transported from nearby cities.

Estimation of the PM2.5 effective hygroscopic parameter and water content based on particle chemical composition: Methodology and case study

Particle hygroscopicity plays a key role in understanding the mechanisms of haze formation and particle optical properties. The present study developed a method for predicting the effective hygroscopic parameter ĸ and the water content of PM2.5 on the basis of the ĸ-Kohler theory and bulk chemical components of PM2.5. Our study demonstrated that the effective hygroscopic parameter can be estimated using the PM2.5 mass concentration, water-soluble ions, and total water-soluble carbon. By combining the estimated ĸ and ambient relative humidity, the water content of PM2.5 can be further estimated. As an example, the ĸ and water content of PM2.5 in Beijing were estimated utilizing the method proposed in this study. The annual average value of ĸ of PM2.5 in Beijing was 0.25±0.09, the maximum ĸ value 0.26±0.08 appeared in summer, and the seasonal variation is insignificant. The PM2.5 water content was determined by both the PM2.5 hygroscopicity and the ambient relative humidity (RH). The annual average mass ratio of water content and PM2.5 was 0.18±0.20, and the maximum value 0.31±0.25 appeared in summer. Based on the estimated water content of PM2.5 in Beijing, the relationship between the PM2.5 water content and RH was parameterized as: m (%) = 0.03 × (5.73×10-8) × RH3.72. This parametric formula helps to characterize the relationship between the PM2.5 mass concentration and atmospheric visibility.

Inversion of the haze aerosol sky columnar AVSD in central China by combining multiple ground observation equipment.

Wuhan is the biggest city in China that has been facing an increasingly serious problem of air pollution in the recent years. In order to understand the mechanism of haze formation and diffusion, it is very important to obtain multiple atmospheric parameters. Columnar aerosol volume size distribution (AVSD) is an important atmospheric parameter in this regard, and utilizing CIMEL sun-photometer data to obtain this parameter has become the most popular method. However, currently, the widely used retrieval algorithms cannot be accessed using an open source code, and thus the retrieval of columnar AVSD is still a challenging task.. In this article, we introduce a new method that combines partial least squares (PLS) and genetic algorithm (GA) for the retrieval of columnar AVSD. By using this new method, we could obtain credible results even during hazy periods, despite the fact that our sun-photometer did not participate in the AERONET program and we did not use an official data processing method. First, it was assumed that columnar AVSD obeys the double logarithmic normal distribution function. Second, the relationship between the columnar AVSD and the AVSD on earth's surface was established using the partial least squares (PLS) method. Finally, the initial distribution parameters were adjusted through GA to obtain an optimal solution. This new method can improve the accuracy and reduce the computational difficulties faced in the retrieval of columnar AVSD in the absence of AREONET-based algorithm.

One year online measurements of water-soluble ions at the industrially polluted town of Nanjing, China: Sources, seasonal and diurnal variations

Half-hourly mass concentrations water-soluble ions (WSIs) and PM2.5 were measured online a Rapid Collector of Fine Particles and Ion Chromatography system (RCFP-IC) and FH62C14 Continuous Particulate Monitor in Nanjing from October 18, 2013 to November 17, 2014. The WSIs concentration ranged from 7.07 to 333.42 μg m−3 with an annual mean of 76.32 μg m−3. The WSIs ranked in the order of SO42− > NH4+ > NO3− > Cl− > NO2− > K+ > Ca2+ > Na+ > Mg2+. The PM2.5 concentration ranged from 4.00 to 400 μg m−3 with an annual mean of 83.58 μg m−3. The concentrations of WSIs varied in the order of winter (115.77 μg m−3) > spring (76.10 μg m−3) > autumn (63.72 μg m−3) > summer (59.75 μg m−3), with the highest level in January (123.99 μg m−3) and lowest level in August (43.73 μg m−3). Different WSIs had distinct diurnal variations. The source analysis of the WSIs in the PCA/APCS mode illustrated that the sources consisted of secondary aerosol, coal combustion, mineral dust, biomass burning, traffic emissions and sea salt. In addition, there were seasonal variations amongst the various sources. The haze formation mechanism was different in summer and winter. The winter was dominated by NH4NO3 (18.56%), (NH4)2SO4 (28.63%), NH4+ (11.27%), SO42− (18.35%) and NO3− (13.13%), and by NH3 (25.93%), (NH4)2SO4 (13.37%), SO42− (15.74%) and NO3− (9.97%) in summer. Consequently, the proportions of HCl, HNO3, NH4+, SO42− and NO3− were much larger during haze episodes in winter, while it was dominated by NH4NO3, NH4+, (NH4)2SO4, SO42− and NO3− during summer haze episodes.