PM2.5 in China: Measurements,sources, visibility and health effects,and mitigation

Concern over the health effects of fine particles in the ambient environment led the U.S. Environmental Protection Agency to develop the first standard for PM_2.5 (particulate matter less than 2.5 μm) in 1997. The Particle Technology Laboratory at the University of Minnesota has helped to establish the PM_2.5 standard by developing many instruments and samplers to perform atmospheric measurements. In this paper, we review various aspects of PM_2.5, including its measurement, source apportionment, visibility and health effects, and mitigation. We focus on PM_2.5 studies in China and where appropriate, compare them with those obtained in the U.S. Based on accurate PM_2.5 sampling, chemical analysis, and source apportionment models, the major PM_2.5 sources in China have been identified to be coal combustion, motor vehicle emissions, and industrial sources. Atmospheric visibility has been found to correlate well with PM_2.5 concentration. Sulfate, ammonium, and nitrate carried by PM_2.5, commonly found in coal burning and vehicle emissions, are the dominant contributors to regional haze in China. Short-term exposure to PM_2.5 is strongly associated with the increased risk of morbidity and mortality from cardiovascular and respiratory diseases in China. The strategy for PM_2.5 mitigation must be based on reducing the pollutants from the two primary sources of coal-fired power plants and vehicle emissions. Although conventional Particulate Emission Control Devices (PECD) such as electrostatic precipitators in Chinese coal-fired power plants are generally effective for large particles, most of them may not have high collection efficiency of PM_2.5. Baghouse filtration is gradually incorporated into the PECD to increase the PM_2.5 collection efficiency. By adopting stringent vehicle emissions standard such as Euro 5 and 6, the emissions from vehicles can be gradually reduced over the years. An integrative approach, from collaboration among academia, government, and industries, can effectively manage and mitigate the PM_2.5 pollution in China.     

Regional source contributions to fine particulate matter of less studied cities in Beijing-Tianjin-Hebei region in 2017

Located in the central area of the North China Plain, the Beijing-Tianjin-Hebei region experiences severe air pollution, especially for Hebei province with five cities among the top 10 cities with the worst air quality nationwide. However, less studies have investigated local and regional contributions to cities in Hebei in comparison to Beijing and Tianjin. In this study, a source-oriented version of the Community Multiscale Air Quality (CMAQ) model is used to quantify inter- and intra-province transport of PM_2.5 in 11 cities within Hebei in 2017. PM_2.5 and its components vary seasonally with high levels in winter and low levels in summer. Local contributions to total PM_2.5 within cities are 23%–61%, while intra-province transport contributes 10%–30%, and inter-province transport contributes 23%–46%, with top contributors of Shandong (4%–22%), Henan (3%–15%) and Shanxi (2%–11%). The primary components in most cities are mainly from local sources (30%–80%), and the secondary components are mainly from inter-province contributions (30%–66%). Local sources have the highest contributions to total PM_2.5 in Shijiazhuang (∼49%), followed by Shanxi (∼12%) and Xingtai (∼7%). Secondary components from local and intra-province emissions are the major cause of heavy pollution events. These results suggest that both local and regional joint control measures with neighboring cities and provinces are necessary for pollution reduction in Hebei cities.     

Variation of PM2.5 concentration in Hangzhou,China

This observational study investigates the variation of PM_2.5 concentration and its ratio against PM₁₀ concentration under different weather systems and pollution types. The study was conducted in Hangzhou on east China's Yangtze River Delta using data collected at seven ambient air quality monitoring stations around the metropolitan area between 2006 and 2008 and using weather information in the same period. Nine predominant weather systems affecting the city were classified through careful analysis of the 11-year surface and upper air weather charts from 1996 to 2006. Each observational day was then assigned to one of the nine weather systems. It was found that the PM_2.5 concentration varied greatly for different weather systems, with the highest PM_2.5 concentration associated with the post-cold-frontal system at 0.091 mg/m³ and the lowest PM_2.5 concentration with the easterlies system at 0.038 mg/m³, although the PM_2.5/PM₁₀ ratio remained consistently above 0.5 for all systems. The post-cold-frontal system typically occurs in autumn and winter while the easterlies system is more a summer phenomenon. Among all types of pollution, the highest PM_2.5 concentration of 0.117 mg/m³ coincided with the large-scale continuous pollution events, suggesting that this type of pollution was more conducive to the formation of secondary particulate matters. The ratio of PM_2.5/PM₁₀ was above 0.5 in non-pollution days and all pollution types but one under the influence of dust storms when the ratio decreased to 0.3 or less. The outcomes of this study could be used to develop a rudimental predictive model of PM_2.5 concentration based on weather system and pollution type.     

Composition of carbohydrates,surfactants, major elements and anions in PM2.5 during the 2013 Southeast Asia high pollution episode in Malaysia

Haze episodes have become a major concern in Malaysia over the past few decades and have an increasingly important impact on the country each and every year. During haze episodes from biomass burning in Southeast Asia, particularly from Sumatra, Indonesia, particulate matter PM_2.5 is found to be one of the dangerous sources of airborne pollution and is known to seriously affect human health. This study determines the composition of carbohydrates (as levoglucosan), surfactants, major elements, and anions in PM_2.5 during a 2013 haze episode. PM_2.5 samples were collected from Universiti Kebangsaan Malaysia, Bangi, using a high volume sampler during a seven-day monitoring campaign during the peak of that year’s haze episode. PM_2.5 concentrations ranged between 14.52 and 160.93 μg/m³, exceeding the 2005 WHO air quality guidelines for PM_2.5 (25 μg/m³ for 24-h mean). The patterns for levoglucosan, surfactants, major elements, and anionic compositions were proportional to the PM_2.5 concentrations. Changes in PM_2.5 observed on days 3 and 4 were influenced by a combination of meteorological factors, which substantiate the theory that such factors play a pivotal role in haze episodes.     

Multiyear analyses of ground-level air contaminants over Paris metropolitan region using real-time observations and air mass backward trajectories

For the years 2008–2013, particles of diameter <10 and 2.5 μm (PM₁₀ and PM_2.5, respectively), NO_x, SO₂, and O₃ concentrations at urban, suburban, rural, and traffic sites in the Paris metropolitan area were analyzed. Strong spatial variability at traffic and rural sites and relatively uniform profiles at urban and suburban sites for PM₁₀, PM_2.5, and O₃ were observed. The O₃ weekend effect was induced by lower NO_x emissions during the weekend, and favored volatile organic compounds (VOCs)-limited atmospheric conditions. In conjunction with low ambient temperature, these conditions could also favor increased formation of secondary particulate nitrates in winter. Winter air pollution events were associated with multiple pollutants, whereas those observed in spring were caused by high PM₁₀ and PM_2.5 levels. Backward trajectory analyses showed the contribution of sources in Western and Central Europe on days with high PM₁₀, PM_2.5, and O₃, and a local/national component for NO_x and SO₂.     

An evaluation of mass,number concentration,chemical composition and types of particles in a cafeteria before and after the passage of an antismoking law

This study assessed air quality indicators before and after enactment of the Spanish anti-smoking law. Mass and number concentrations and the chemical composition of particles were evaluated. Microscopy analyses were also conducted. Real time concentrations of PM₁₀, PM_2.5, PM₁ and ultrafine particles were measured under ventilated and non-ventilated conditions and PM₁₀ samples were collected for detailed inorganic and organic chemical characterization. Before enactment of the law in 2010, tobacco smoke produced significant indoor ambient particulate matter pollution, with elevated particulate matter mass concentrations (PM₁₀ and PM₁ concentrations of 122–220 and 48–85 μg/m³, respectively) and ultrafine particle numbers (75,000 and 48,000 cm^–3 under ventilated and non-ventilated conditions, respectively). Typical tobacco smoke tracers including iso- and anteiso-alkanes and elements including La and Ce from the ignition of lighters were abundant. Additionally, several toxic substances derived from tobacco smoke, including Cd (3.1 ng/m³) and benzo[a]pyrene (1.0 ng/m³) were present at concentrations approximately 10 times greater than those measured after enactment of the anti-smoking law. The anti-smoking law significantly reduced exposure to potentially toxic compounds by approximately 90%. This law is expected to have a positive health impact, particularly for people who spend considerable time in affected environments, such as employees.     

Rational designed ZIF-8@PDA@PDMS composite sponge for efficient and sustainable particulate matter filtering under harsh environment

Particulate matter (PM) is a significant danger to both environment and human health. Despite the development of a series of air filters, they do not work well in harsh environment such as high temperature, high humidity or long-time filtration. To make a three-dimensional (3D) particle capture device, a sacrificial template approach was used to manufacture polydimethylsiloxane (PDMS) sponge, and then zeolite imidazole framework-8 (ZIF-8) was grown in situ on the 3D network of PDMS sponge. The removal efficiency of PM_2.5 or PM₁₀ is greater than 99.8% because of the high specific surface area and porous network structure of PDMS sponge, as well as the large number of metal sites of ZIF-8. In addition, the sponge filter has long-term filtration stability and still achieves excellent performance after 65 h of filtration. The composite sponge can adapt to harsh environments such as high temperature (250 °C) and high humidity (90% RH). Composite sponge filter has a regular shape, and it may be customized to any shape as required. This study provides a new idea for designing 3D high-efficiency air filters that can adapt to harsh environments.     

Chemical components of PM2.5 in different seasons in Harbin,China

The seasonal characteristics of fine particulate matter (PM_2.5) were investigated from October 2020 to April 2021 (spreading fall, winter and spring) in Harbin, a city located in northeast China. The mass concentrations of PM_2.5 in winter were significantly higher than those in fall and spring. Moreover, our results indicated that various aerosol species had obvious seasonality. The proportions of secondary components were higher in winter than other two seasons. In contrast, the ratios of nitrate to sulfate (NO₃⁻/SO₄²⁻) showed lower levels in winter, which was because both the ratios of nitrogen dioxide to sulfur dioxide (NO₂/SO₂) and the ratios of nitrogen oxidation ratio to sulfur oxidation ratio (NOR/SOR) exhibited lower values in winter than in fall and spring. With PM_2.5 increased, the NO₃⁻/SO₄²⁻ ratios showed increasing trends in all three seasons, which was mainly attributed to the increase of NOR/SOR ratios in fall and spring, and the increase of both NO₂/SO₂ and NOR/SOR ratios in winter. This result highlighted that nitrate was more important than sulfate as a driver for the growth of PM_2.5 during the period of heavy air pollution. Additionally, the sources of organic aerosol (OA) in different seasons were also distinctly different. Overall, the sum of biomass burning OA (BBOA) and secondary OA (SOA) contributed >70% of OA in three seasons. The fractional contributions of BBOA to total OA, notably, exhibited higher levels in fall and spring, because of intensive open agricultural fires. The SOA fractions in OA were larger in winter, likely due to higher relative humidity which facilitated the secondary formation. A large increase in the proportions of BBOA was observed during polluted days in fall and spring compared to clean days. In comparison, during heavily-polluted periods, secondary formation made a dominant contribution to organic matter in winter.     

PM2.5 in an industrial district of Zhengzhou,China: Chemical composition and source apportionment

Zhengzhou is a developing city in China, that is heavily polluted by high levels of particulate matter. In this study, fine particulate matter (PM_2.5) was collected and analyzed for their chemical composition (soluble ions, elements, elemental carbon (EC) and organic carbon (OC)) in an industrial district of Zhengzhou in 2010. The average concentrations of PM_2.5 were 181, 122, 186 and 211 μg/m³ for spring, summer, autumn and winter, respectively, with an annual average of 175 μg/m³, far exceeding the PM_2.5 regulation of USA National Air Quality Standards (15 μg/m³). The dominant components of PM_2.5 in Zhengzhou were secondary ions (sulphate and nitrate) and carbon fractions. Soluble ions, total carbon and elements contributed 41%, 13% and 3% of PM_2.5 mass, respectively. Soil dust, secondary aerosol and coal combustion, each contributing about 26%, 24% and 23% of total PM_2.5 mass, were the major sources of PM_2.5, according to the result of positive matrix factorization analysis. A mixed source of biomass burning, oil combustion and incineration contributed 13% of PM_2.5. Fine particulate matter arising from vehicles and industry contributed about 10% and 4% of PM_2.5, respectively.     

Particulate pollution in an underground car park in Wuhan,China

Particulate matter (PM) pollution in an underground car park in Wuhan was investigated. Mass concentrations of PM₁₀ and PM_2.5 were obtained using gravimetric method. Selected metal elements, such as Fe, Mn, Zn, Pb, and Cu in PM₁₀ samples, were determined using atomic absorption spectrometer (AAS). Beta attenuation method was applied to observe the hourly variation of PM₁₀ levels. Results show that average PM₁₀ concentrations at the entrance and at the exit were 101.3 μg/m³ and 234.4 μg/m³, respectively, and average PM_2.5 concentrations at the entrance and at the exit were 47.7 μg/m³ and 62.7 μg/m³, respectively. PM pollution was worse at the exit than at the entrance. Hourly PM₁₀ concentration was weakly correlated with traffic flow. Regarding element concentrations, the most enriched element in PM₁₀ samples was Fe. Re-suspension of soil dust at the exit is an important source of PM₁₀.     

Seasonal characteristics and provenance of organic aerosols in the urban atmosphere of Liaocheng in the North China Plain: Significant effect of biomass burning

To better understand the seasonal characteristics of urban organic aerosol (OA) in the North China Plain (NCP), PM_2.5 samples in the urban atmosphere of Liaocheng were collected and analyzed. The molecular distribution of the organic markers in the urban atmosphere of Liaocheng reveals that n-alkanes (39.3%) was the most abundant species all year round, followed by saccharides (28.2%), phthalic acids (Ph, 20.8%), biogenic secondary organic aerosol (BSOA) tracers (9.4%), and polycyclic aromatic hydrocarbon (PAHs, 2.3%). PM_2.5, organic carbon (OC), elemental carbon (EC), and primary organic markers exhibit the highest concentrations in winter, due largely to the increased biomass burning and coal combustion for house heating in local and surrounding regions. However, the concentration and relative abundance of BSOA are significantly higher in summer than other seasons, induced by the more favorable meteorological conditions that would promote the emissions of biogenic volatile organic compounds (BVOCs) and the secondary production of BSOA. The ratios of OC/EC and 3-methyl-1,2,3-butanetricarboxylic acid to cis-pinic acid plus cis-pinonic acid (MBTCA/(PA + PNA) are higher in the warm seasons than those in the cold seasons, indicating that the oxidation of OA is sensitive to air temperature. Compared to 2017, the concentration level of PAHs during wintertime decreased by 40.8%, confirming that the stringent regulation of coal burning is effective. The highest concentration of high molecular weight (HMW) n-alkanes and three anhydrosugars in winter, and the close correlation of levoglucosan with HMW n-alkanes suggests that the impact of biomass burning was more significant in winter. The same seasonal characteristic of the ratios of high-/low-NO_x products with NO_x and the strong correlation of high-/low-NO_x products with levoglucosan indicate that the formation of isoprene SOA (SOA_I) tracers was significantly influenced by anthropogenic emissions. The molecular compositions, the distributions of fire spots, backward trajectories of air masses, and correlation analysis suggest that air pollution events in spring were primarily resulted from biomass burning and secondary oxidation, while pollution events in winter were largely driven by the increased combustion sources, and promoted aqueous secondary formation. Our results suggest that the reduction of biomass and coal combustion should be taken into account to improve the urban air quality in the NCP.     

Impact of meteorological conditions on a nine-day particulate matter pollution event observed in December 2013, Shanghai,China

A severe particulate matter pollution event occurred in Shanghai from 1 to 9 December 2013. The mean hourly mass concentrations of PM_2.5 and PM₁₀ were 211.9 and 249.0 μg/m³, respectively. Reanalysis data, in situ, and remote-sensing measurements were used to examine the impacts of meteorological conditions on this event. It was found that the synoptic pattern of weak pressure, the reduced planetary boundary layer height, and the passage of two cold fronts were key factors causing the event. Four stages were identified during this event based on the evolution of its PM_2.5 levels and weather conditions. The highest concentration of PM_2.5 (602 μg/m³) was observed in stage 3. High PM_2.5 concentrations were closely associated with a low local ventilation index, with an average of 505 m²/s, as well as with the influx of pollutants from upstream, transported by the cold fronts.     

Chemical characteristics of PM2.5 during haze episodes in the urban of Fuzhou,China

Atmospheric fine particles (PM_2.5) were collected in this study with middle volume samplers in Fuzhou, China, during both normal days and haze days in summer (September 2007) and winter (January 2008). The concentrations, distributions, and sources of polycyclic aromatic hydrocarbons (PAHs), organic carbon (OC), elemental carbon (EC), and water soluble inorganic ions (WSIIs) were determinated. The results showed that the concentrations of PM_2.5, PAHs, OC, EC, and WSIIs were in the orders of haze > normal and winter > summer. The dominant PAHs of PM_2.5 in Fuzhou were Fluo, Pyr, Chr, BbF, BkF, BaP, BghiP, and IcdP, which represented about 80.0% of the total PAHs during different sampling periods. The BaPeq concentrations of ∑PAHs were 0.78, 0.99, 1.22, and 2.43 ng/m³ in summer normal, summer haze, winter normal, and winter haze, respectively. Secondary pollutants (SO₄^2?, NO₃^?, NH₄⁺, and OC) were the major chemical compositions of PM_2.5, accounting for 69.0%, 55.1%, 63.4%, and 64.9% of PM_2.5 mass in summer normal, summer haze, winter normal, and winter haze, respectively. Correspondingly, secondary organic carbon (SOC) in Fuzhou accounted for 20.1%, 48.6%, 24.5%, and 50.5% of OC. The average values of nitrogen oxidation ratio (NOR) and sulfur oxidation ratio (SOR) were higher in haze days (0.08 and 0.27) than in normal days (0.05 and 0.22). Higher OC/EC ratios were also found in haze days (5.0) than in normal days (3.3). Correlation analysis demonstrated that visibility had positive correlations with wind speed, and negative correlations with relative humidity and major air pollutants. Overall, the enrichments of PM_2.5, OC, EC, SO₄^2?, and NO₃^? promoted haze formation. Furthermore, the diagnostic ratios of IcdP/(IcdP + BghiP), IcdP/BghiP, OC/EC, and NO₃^?/SO₄^2? indicated that vehicle exhaust and coal consumption were the main sources of pollutants in Fuzhou.     

Chemical characteristics and Pb isotopic compositions of PM2.5 in Nanchang,China

In mid-September 2013, PM_2.5 samples were collected at six sites in Nanchang, Jiangxi Province, China, to quantify nine water-soluble ions (Ca²⁺, Mg²⁺, K⁺, Na⁺, NH₄⁺, SO₄²⁻, Cl⁻, F⁻, NO₃⁻), 29 trace elements (Ba, Zn, Pb, Ni, Mo, Cr, Cu, Sr, Sb, Rb, Cd, Bi, Zr, V, Ga, Li, Y, Nb, W, Cs, Tl, Sc, Co, U, Hf, In, Re, Be, and Ta), and to characterize Pb isotopic ratios (²⁰⁷Pb/²⁰⁶Pb, ²⁰⁸Pb/²⁰⁶Pb, and ²⁰⁷Pb/²⁰⁴Pb) for identifying the main source(s) of Pb. The results showed that the average daily PM_2.5 concentration (53.16 ± 24.17) μg/m³ was within the secondary level of the Chinese ambient air quality standard. The combined concentrations of SO₄²⁻, NH₄⁺, and NO₃⁻ to total measured water-soluble ion concentrations in PM_2.5 ranged from 79.40% to 95.18%, indicating that anthropogenic sources were significant. Coal combustion and vehicle emissions were both contributors to PM_2.5 based on the NO₃⁻/SO₄²⁻ ratios. Wushu School experienced the lowest concentrations of PM_2.5 and most trace elements among the six sampling sites. Enrichment factor results showed that Tl, Cr, In, Cu, Zn, Pb, Bi, Ni, Sb, and Cd in PM_2.5 were affected by anthropogenic activities. Cluster analysis suggested that Cd, Sb, Pb, Re, Zn, Bi, Cs, Tl, Ga, and In were possibly related to coal combustion and vehicle exhaust, while Ni, Nb, Cr, and Mo may have originated from metal smelting. Pb isotopic tracing showed that coal dust, cement dust, road dust and construction dust were the major Pb sources in PM_2.5 in Nanchang. Combined, these sources contributed an average of 72.51% of the Pb measured, while vehicle exhaust accounted for 27.49% of Pb based on results from a binary Pb isotope mixed model.     

Compositional characteristics and toxicological responses of human lung epithelial cells to inhalable particles (PM10) from ten typical biomass fuel combustions

As the primary component of haze, atmospheric inhalable particulate matters (PM₁₀) are highly detrimental to human health. Biomass combustion is one of China's most pivotal sources to aerosols pollution, inducing non-negligible emissions and uncertain risks. PM₁₀ samples directly from 10 representative biomass fuel combustion sources (2 groups covering the reality widely: straws of rice, wheat, corn, corncob, soybean, peanut, rape, sesame; and branches of pine, peach) were collected using the dilution channel sampler and analyzed for chemical compositions and in vitro cytotoxicity to human lung epithelial cell lines A549. The components of PM₁₀ are dominated by organic carbon (OC), followed by water-soluble K⁺ and Cl⁻, and rich in metals Fe, Zn, Cr, and Ni. Generally, PM₁₀ emitted from biomass fuel combustions can weaken the antioxidant capacity of cells, and straws emissions, especially rape and peanut straws, show stronger ability to further induce oxidative stress and inflammatory damage than fuelwoods, owing to the key toxic roles of Cr, Ni, and Co. Therefore, reducing the specific source emissions of PM₁₀ from crop straw combustions rich in heavy metals could be an effective oriented strategy to improve environmental air quality and control aerosols pollution precisely for protecting public health.     

Effect of chemical composition of PM2.5 on visibility in Guangzhou,China, 2007 spring

The object of this study was to investigate the correlation of visibility with chemical composition of PM2.5 in Guangzhou. In April 2007, 28 PM2.5 samples were collected daily at the monitoring station of the South China Institute of Environmental Sciences （SCIES）, in urban Guangzhou. Water-soluble ionic species （CI^-, NO3^-, SO4^2-, NH4^＋, K^＋, Na^＋, Ca^2＋, and Mg^2＋） and carbonaceous contents （OC and EC） of the PM2.5 samples were determined to characterize their impact on visibility impairment. The results showed that sulfate was the dominant species that affected both light scattering and visibility. The average percentage contributions of the visibility-degrading species to light scattering coefficient were 40% for sulfate, 16% for nitrate, 22% for organics, and 22% for elemental carbon. Because of its foremost effect on visibility, sulfate reduction in PM2.5 would effectively improve the visibility of Guangzhou.     

Elemental compositions of PM2.5 and TSP in Lijiang,southeastern edge of Tibetan Plateau during pre-monsoon period

PM_2.5 and total suspended particulate (TSP) samples were collected at Lijiang, southeastern Tibetan Plateau, China. Sixteen elements (Al, Si, S, K, Ca, Cr, Mn, Ti, Fe, Ni, Zn, As, Br, Sb, Pb and Cu) were analyzed to investigate their elemental compositions during the pre-monsoon period. The results showed that Ca was the most abundant element in both PM_2.5 and TSP samples. The enrichment factors (EFs) of Si, Ti, Ca, Fe, K and Mn were all below 10 for both PM_2.5 and TSP, and these elements also had lower PM_2.5/TSP ratios (0.32–0.34), suggesting that they were mainly derived from crustal sources. Elements Cu, Zn, S, Br and Sb showed strong enrichment in PM_2.5 and TSP samples, with their PM_2.5/TSP ratios ranging from 0.66 to 0.97, indicating that they were enriched in the fine fractions and influenced by anthropogenic sources. Analysis of the wind field at 500 hPa and calculations of back trajectories indicated that Al, Si, Ca, Ti, Cr, Mn and Fe can be influenced by transport from northwestern China during the dust-storm season, and that S, K, Ni, Br and Pb reached high concentrations during westerly transport from south Asia. Combined with the principle component analysis and correlation analysis, elements of PM_2.5 samples were mainly from crustal sources, biomass burning emissions and regional traffic-related sources.     

Characterization of summer PM2.5 aerosols from four forest areas in Sichuan,SW China

Aerosol samples were collected over 24 and 12 h to represent day/night aerosol characteristics in forest areas at Ya’an Baima Spring Scenic Area (BM), Panzhihua Cycas National Nature Reserve (PZ), Gongga Mountain National Nature Reserve (GG), and Wolong National Nature Reserve (WL), during the summers of 2010–2012. Mass and chemical component concentrations, including organic carbon, elemental carbon, and inorganic ions (F⁻, Cl⁻, NO₂⁻, NO₃⁻, SO₄²⁻, C₂O₄²⁻, PO₄³⁻, K⁺, Na⁺, Ca²⁺, Mg²⁺, and NH₄⁺), of PM_2.5 aerosols were measured. The average PM_2.5 concentrations for 24 h were 72.42, 104.89, 20.55, and 29.19 μg/m³ at BM, PZ, GG, and WL, respectively. Organic matter accounted for 38.0–49.3%, while elemental carbon accounted for 2.0–5.7% of PM_2.5 mass. The sum concentrations of SO₄²⁻, NH₄⁺, and NO₃⁻ accounted for 23.0%, 17.4%, 22.1%, and 30.5% of PM_2.5 mass at BM, PZ, GG, and WL, respectively. Soil dust was also an important source of PM_2.5, accounting for 6.3%, 17.0%, 10.4%, and 19.1% of PM_2.5 mass at BM, PZ, GG, and WL, respectively. These reconstructed masses accounted for 75.9–102.0% of PM_2.5 mass from the four forest areas of SW China.     

Analysis of the causes of heavy aerosol pollution in Beijing,China: A case study with the WRF-Chem model

The causes and variability of a heavy haze episode in the Beijing region was analyzed. During the episode, the PM_2.5 concentration reached a peak value of 450 μg/kg on January 18, 2013 and rapidly decreased to 100 μg/kg on January 19, 2013, characterizing a large variability in a very short period. This strong variability provides a good opportunity to study the causes of the haze formation. The in situ measurements (including surface meteorological data and vertical structures of the winds, temperature, humidity, and planetary boundary layer (PBL)) together with a chemical/dynamical regional model (WRF-Chem) were used for the analysis. In order to understand the rapid variability of the PM_2.5 concentration in the episode, the correlation between the measured meteorological data (including wind speed, PBL height, relative humidity, etc.) and the measured particle concentration (PM_2.5 concentration) was studied. In addition, two sensitive model experiments were performed to study the effect of individual contribution from local emissions and regional surrounding emissions to the heavy haze formation. The results suggest that there were two major meteorological factors in controlling the variability of the PM_2.5 concentration, namely, surface wind speed and PBL height. During high wind periods, the horizontal transport of aerosol particles played an important role, and the heavy haze was formed when the wind speeds were very weak (less than 1 m/s). Under weak wind conditions, the horizontal transport of aerosol particles was also weak, and the vertical mixing of aerosol particles played an important role. As a result, the PBL height was a major factor in controlling the variability of the PM_2.5 concentration. Under the shallow PBL height, aerosol particles were strongly confined near the surface, producing a high surface PM_2.5 concentration. The sensitivity model study suggests that the local emissions (emissions from the Beijing region only) were the major cause for the heavy haze events. With only local emissions, the calculated peak value of the PM_2.5 concentration was 350 μg/kg, which accounted for 78% of the measured peak value (450 μg/kg). In contrast, without the local emissions, the calculated peak value of the PM_2.5 concentration was only 100 μg/kg, which accounted for 22% of the measured peak value.     

Variations of aminiums in fine particles at a suburban site in Guangzhou,China: Importance of anthropogenic and natural emissions

Amines are important nitrogen-containing compounds in fine particles (PM_2.5) in the atmosphere. Observations are necessary for in-depth understanding on the characteristics, sources and atmospheric processes of aminiums. In this study, the observation of ten C₁–C₄ aminiums in PM_2.5 was conducted in January and March of 2021 in suburban Guangzhou. The concentration and composition of aminiums showed significant differences between the pollution episodes and non-episode periods. Seasonal difference was also observed between winter and spring. The influence of meteorological factors (i.e., wind speed, atmospheric pressure, temperature and relative humidity) was investigated. The variations of aminiums were also affected by different sources. Anthropogenic sources were suggested to be major contributor to aminiums in the pollution episodes, while biological sources were important sources to aminiums in the non-episode periods, especially in spring. Positive matrix factorization receptor model was applied to investigate the source contributions, and four major sources were identified. The results show that vehicular emission, industrial production, biological emission and soil/dust were the major sources of aminiums. This study emphasizes the importance of source contribution and meteorological conditions on the variations of aminiums, which provides further understanding of organic nitrogen in the atmosphere.