Secondary Sulfate Research Articles

Source apportionment of PM2.5 using online and offline measurements of chemical components in Tianjin, China

PM2.5 and chemical species of water-soluble inorganic ions, carbon components as well as elements were simultaneously measured by online and offline methods in Tianjin, China. Online measured PM2.5, total carbon, and major ions showed good agreement with offline results (r > 0.7), while obvious differences were found for most elements with correlation coefficients lower than 0.6. Online measured ions and most elements (except As, Ca, Ni) showed higher or comparable estimated annual average concentrations than offline results. Sources of PM2.5 were identified by using Positive Matrix Factorization (PMF) model respectively with online and offline data. Higher contributions of secondary source (38%) and secondary sulfate (11%) for online method could be partly caused by higher concentrations of SO42− and NO3− compared to offline method (30%, 10%). Lower source contribution of dust for online (4%) method might partly relate to lower concentration of Ca compared to offline measurement (7%). Different source contribution estimates of vehicle emission and coal combustion between online (18%, 24%) and offline (21%, 25%) may be partly linked to variation of concentrations of OC and EC resulted from different analytical methods. Industrial source, and sea salt & biomass burning showed lower source contributions both online (4%, 1%) and offline (5%, 2%).

In Situ Observations of Light‐Absorbing Carbonaceous Aerosols at Himalaya: Analysis of the South Asian Sources and Trans‐Himalayan Valleys Transport Pathways

AbstractThe mountain‐valleys along the south margin of the Himalaya‐Tibetan Plateau (HTP), referred to as trans‐Himalayan valleys, are transport pathways of atmospheric pollutants from the South Asia lifting to the HTP based on atmospheric models and satellite detections. However, few field studies can be conducted to confirm the aerosol transport along these valleys due to the harsh environment and limited power supply. Individual particle collection instruments offer the unique advantage of collecting samples and tracing particle sources in remote areas due to their portability and efficiency. In this study, transmission electron microscopy was used to study individual particles collected in two trans‐Himalayan valleys. We found that 49–70% of thousands of particles were light‐absorbing carbonaceous aerosols including soot‐bearing and tarball‐bearing particles in December of 2017. The dominant sizes of soot‐bearing and tarball‐bearing particles were 151–370 and 198–255 nm, respectively. The WRF‐Chem model and wind field analyses show that the intense regional air pollution with high mass concentrations of light‐absorbing carbonaceous aerosol occurred in the South Asia and southwest wind normally prevailed along the trans‐Himalayan valleys in the afternoon of each day during wintertime. Backward trajectory and CALIPSO data further confirm that these light‐absorbing carbonaceous aerosols from the South Asia were transported to the southern HTP. These carbonaceous aerosols exhibited significantly internally mixing with secondary sulfates. Here individual particle analysis coupled with the WRF‐Chem model, the meteorological observation data, and satellite data confirm the trans‐Himalayan valleys as the direct channels for abundant carbonaceous aerosols lifting from the South Asia to the HTP.

Insights into chemical composition, abatement mechanisms and regional transport of atmospheric pollutants in the Yangtze River Delta region, China during the COVID-19 outbreak control period

To investigate chemical characteristics, abatement mechanisms and regional transport of atmospheric pollutants during the COVID-19 outbreak control period in the Yangtze River Delta (YRD) region, China, the measurements of air pollutants including fine particulate matter (PM2.5) and volatile organic compounds (VOCs) on non-control period (NCP, 24 December 2019–23 January 2020) and control period (CP, 24 January–23 February 2020) were analyzed at the urban Pudong Supersite (PD) and the regional Dianshan Lake Supersite (DSL). Due to the stricter outbreak control, the levels of PM2.5 and VOCs, and the occurrence frequencies of haze-fog episodes decreased substantially from NCP to CP, with average reduction rates of 31.6%, 38.9% and 35.1% at PD, and 34.5%, 50.7% and 37.9% at DSL, respectively. The major source for PM2.5 was secondary sulfate & nitrate in both periods, and the emission control of primary sources such as coal burning and vehicle exhaust decreased the levels of precursors gas sulfur dioxide and nitrogen oxide, which highly contributed to the abatement of PM2.5 from NCP to CP. The higher levels of ozone at both PD and DSL on CP might be due to the weak nitrogen monoxide titration, low relative humidity and high visibility compared with NCP. Vehicle exhaust and fugitive emission from petrochemical industry were the major contributors of ambient VOCs and their decreasing activities mainly accounted for VOCs abatement. Moreover, the high frequency of haze-fog events was closely impacted by medium-scale regional transport within Anhui and Jiangsu provinces. Therefore, the decreasing regional transported air pollutants coincided with the emission control of local sources to cause the abatement of haze-fog events in YRD region on CP. This study could improve the understanding of the change of atmospheric pollutants during the outbreak control period, and provide scientific base for haze-fog pollution control in YRD region, China.

Vertical distribution of particle-phase dicarboxylic acids, oxoacids and <i>α</i>-dicarbonyls in the urban boundary layer based on the 325 m tower in Beijing

Abstract. Vertical distributions of dicarboxylic acids, oxoacids, α-dicarbonyls and other organic tracer compounds in fine aerosols (PM2.5) were investigated at three heights (8, 120 and 260 m) based on a 325 m meteorological tower in urban Beijing in the summer of 2015. Results showed that the concentrations of oxalic acid (C2), the predominant diacid, were more abundant at 120 m (210±154 ng m−3) and 260 m (220±140 ng m−3) than those at the ground surface (160±90 ng m−3). Concentrations of phthalic acid (Ph) decreased with the increase in height, indicating that local vehicular exhausts were the main contributor. Positive correlations were noteworthy for C2 ∕ total diacids with mass ratios of C2 to main oxoacids (Pyr and ωC2) and α-dicarbonyls (Gly and MeGly) in polluted days (0.42≤r2≤0.65), especially at the ground level. In clean days, the ratios of carbon content in oxalic acid to water-soluble organic carbon (C2−C ∕ WSOC) showed larger values at 120 and 260 m than those at the ground surface. However, in polluted days, the C2−C ∕ WSOC ratio mainly reached its maximum at ground level. These phenomena may indicate the enhanced contribution of aqueous-phase oxidation to oxalic acid in polluted days. Combined with the influence of wind field, total diacids, oxoacids and α-dicarbonyls decreased by 22 %–58 % under the control on anthropogenic activities during the 2015 Victory Parade period. Furthermore, the positive matrix factorisation (PMF) results showed that the secondary formation routes (secondary sulfate formation and secondary nitrate formation) were the dominant contributors (37 %–44 %) to organic acids, followed by biomass burning (25 %–30 %) and motor vehicles (18 %–24 %). In this study, the organic acids at ground level were largely associated with local traffic emissions, while the long-range atmospheric transport followed by photochemical ageing contributed more to diacids and related compounds in the urban boundary layer than the ground surface in Beijing.

Source apportionment of PM2.5 and its optical properties during a regional haze episode over north China plain

Based on the data of air pollutants in a typical regional haze pollution episode over North China Plain (NCP) in November 2018, Positive matrix factorization (PMF), potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) models were used to analyze the sources and affecting areas of PM2.5 under different development stages. The whole observation period was divided into 6 segments (clean days, fog process, haze process including three stages of I: accumulation, II: growth, III: explosion, and dry haze process) according to PM2.5 concentration, visibility and relative humidity (RH). The dominant source in clean days was soil dust, with contribution percentage of 30.0%. The contributions of coal combustion and secondary nitrate increased with the development of haze pollution, while those of photochemical product, soil dust and secondary sulfate decreased. Coal combustion contributed the most in stage III (35.8%), indicating that the local coal combustion emission was the main reason for the rapid explosion of pollutants. The contribution of vehicular emission was 16.7%, 30.1% and 12.8% in stage I, II, and III, respectively, which was 2.1, 3.8, and 1.6 times that on clean days, presenting significant regional distribution characteristics. The significant local contribution and short-range transport were the major sources of haze pollution episodes in NCP, and Xianghe will bring pollutants to its northeast and southwest directions in the future. (NH4)2SO4, NH4NO3, and organic matter (OM) were the major components of aerosol extinction coefficient (bext) under all development stages, together accounting for 59.5%–78.6%. With the development of haze process, the contribution of (NH4)2SO4 to bext decreased, while that of NH4NO3 increased.

Stable Isotopes of Nitrate, Sulfate, and Carbonate in Soils From the Transantarctic Mountains, Antarctica: A Record of Atmospheric Deposition and Chemical Weathering

Soils in ice-free areas in Antarctica are recognized for their high salt concentrations and persistent arid conditions. While previous studies have investigated the distribution of salts and potential sources in the McMurdo Dry Valleys, logistical constraints have limited our investigation and understanding of salt dynamics within the Transantarctic Mountains. We focused on the Shackleton Glacier (85° S, 176° W), a major outlet glacier of the East Antarctic Ice Sheet located in the Central Transantarctic Mountains (CTAM), and collected surface soil samples from 10 ice-free areas. Concentrations of water-soluble nitrate (NO3¬-) and sulfate (SO42-) ranged from <0.2 to ~150 µmol g-1 and <0.02 to ~450 µmol g-1, respectively. In general, salt concentrations increased with distance inland and with elevation. However, concentrations also increased with distance from current glacial ice position. To understand the source and formation of these salts, we measured the stable isotopes of dissolved NO3- and SO42-, and soil carbonate (HCO3- + CO32-). δ15N-NO3 values ranged from -47.8 to 20.4‰ and, while all δ17O-NO3 values are positive, they ranged from 15.7 to 45.9‰. δ34S-SO4 and δ18O-SO4 values ranged from 12.5 and 17.9‰ and -14.5 to -7.1‰, respectively. Total inorganic carbon isotopes in total bulk soil samples ranged from 0.2 to 8.5‰ for δ13C and -38.8 to -9.6‰ for δ18O. A simple mixing model indicates that NO3- is primarily derived from the troposphere (0-70%) and stratosphere (30-100%). SO42- is primarily derived from secondary atmospheric sulfate (SAS) by the oxidation of reduced sulfur gases and compounds in the atmosphere by H2O2, carbonyl sulfide (COS), and ozone. Calcite and perhaps nahcolite (NaHCO3) are formed through both slow and rapid freezing and/or the evaporation/sublimation of HCO3 + CO3-rich fluids. Our results indicate that origins of salts from ice-free areas within the CTAM represent a complex interplay of atmospheric deposition, chemical weathering, and post-depositional processes related to glacial history and persistent arid conditions. These findings have important implications for the use of these salts in deciphering past climate and atmospheric conditions, biological habitat suitability, glacial history, and can possibly aid in our future collective understanding of salt dynamics on Mars.

Vanadium in slags from smelting of African Pb-Zn vanadate ores: Mineralogy, extractability and potential recovery

Slags originating from the metallurgical processing of Pb-Zn vanadate ores at Berg Aukas (Namibia) and Kabwe (Zambia) contain interestingly high concentrations of V (3750–6140 mg/kg) and can be considered potential sources of this metal. We focused on the mineralogical determination of the major V-bearing phases in these slags using a combination of mineralogical methods (XRD, SEM/EDS, EPMA) and found that V is mainly bound in clinopyroxene (Berg Aukas) and glass/vanadates (Kabwe). The abiotic extraction tests, simulating a hydrometallurgical recovery via agitation leaching, were carried out in 0.5 mol/l sulfuric acid (25 °C and 70 °C, pulp density of 1%) to determine the release of V (and other metals: Pb, Zn) from these slags. The leaching of the metals attained a steady state after 24 h and was systematically higher for the high-temperature trials. There was an incomplete dissolution of V-bearing clinopyroxene from the Berg Aukas slags, as opposed to the much higher extractabilities of V (>80%) observed for the Kabwe slags. Compared to the relatively high Zn extractabilities (>72%), lower yields were observed for Pb due to massive formation of secondary Pb sulfate (anglesite) as confirmed by the PHREEQC-3 calculations and the mineralogical investigation of the slag residues. Due to the high expenses related to the mechanical sample treatment and chemical extraction and low prices of V and Zn, the recovery of these metals from the studied slags is currently non-economical. However, the Kabwe slags have a much higher potential for secondary metal recovery in the future, because they are relatively fine-grained and the extraction could potentially be carried out on the as-is materials without expensive comminution processes (crushing/milling).

Assessment of the PM2.5 oxidative potential in a coastal industrial city in Northern France: Relationships with chemical composition, local emissions and long range sources

The objective of this work was to relate PM2.5 Oxidative Potential (OP) data to PM composition and PM local and distant source contributions. PM2.5 collected in Dunkerque, a coastal industrial city in North of France, was extensively characterized for major and minor chemical species. PM2.5 filters were extracted using a synthetic pulmonary fluid to achieve OP estimation based on Ascorbic Acid (AA) and dithiothreitol (DTT) depletion assays. In order to evidence relationships between OP values, chemical composition and local and distant source contributions, correlation coefficient, Principal Component Analysis (PCA), concentration roses, polar plots and concentration weighted trajectories were used. Heterogeneous conclusions were drawn using the three first methods as the bivariate polar plots lead to dismiss some of the correlations evidenced using correlation coefficient and PCA. Both AA and DTT tests appeared complementary as they were not sensitive to the same species/source contribution. The bivariate polar plot representation of OP values versus wind direction and wind speed revealed that PM2.5 concentration and combustion sources were linked to OP-AA, whereas emissions from integrated steelworks, electric steelworks, heavy fuel oil combustion and traffic non-exhaust significantly contribute to OP-DTT. Sea-salts, aged sea-salts, crustal, secondary sulfates and secondary nitrates sources were not found to contribute to OP values. Constant weighted trajectories evidenced several source regions responsible for high OP values with Belgium, Germany, Netherlands and France at the leader position. Contribution of inland regions appeared possibly related to the biomass and traffic related combustion while heavy fuel oil combustion could also be involved in the contribution of marine and coastal areas.

Roles of RH, aerosol pH and sources in concentrations of secondary inorganic aerosols, during different pollution periods

Abstract Secondary inorganic aerosols (SIA, including sulfate, nitrate, and ammonium) were found to be the most dominant aerosol components during haze period. Elucidating the driving factors during liquid-phase reaction formation process of SIA is a key step for understanding the origin of airborne particulate pollution. In this work, we used online instruments and collected hourly concentrations of ions, gases, meteorological parameters in a northern city of China. Source emissions were estimated by receptor model PMF/ME2 pulling run solution (Partial Target Transformation-PMF: PTT-PMF), and six sources were identified (dust, coal combustion, vehicle exhaust, secondary sulfate, secondary nitrate and biomass burning & SOC). pH values were calculated by ISORROPIA-II, with an average value of 4.68. The relationships between RH, pH, source behaviors and concentrations of SIA during different pollution episodes were discussed. Source emissions were found to influence pH and subsequently the SIA; high RH could result in high SIA because aerosol water content in atmosphere increases with RH, which is favorable for liquid-phase reactions. Finally, we employed statistical and machine learning (Random forest classification: RFC) methods to analysis importance of driving factors on SIA formation during different pollution episodes. Results showed precursors, wet conditions, atmospheric oxidation capacity and acidity favor formation of sulfate and nitrate at different pollution levels; changes of gaseous precursors, RH and temperature are more important to determine PM2.5 pollution classification (clean, slightly polluted, moderately polluted, heavily polluted episodes). The findings of this work can provide useful information for better understanding formation mechanism of SIA, mitigating air pollution and improving human health.

Characterization of PM2.5 sources in a Belgrade suburban area: a multi-scale receptor-oriented approach.

Designated as the most harmful for health, PM2.5 aerosol fraction was a subject of our study. It was collected for all four seasons during 2014/15 in the suburban area of Belgrade (Serbia) and analysed for Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Br, As, Ba and Pb elements and for NH4+, NO3- and SO42- ions by particle-induced X-ray emission and ion chromatography techniques, respectively. Obtained concentrations have been treated by a combination of several receptor-oriented models to reveal source contributions to the suburban PM2.5 at different spatial scales. Applied positive matrix factorization analysis indicated five main groups of emission sources: biomass burning (14.5%), traffic (3.9%), regional combustion/secondary sulphates (28.8%), local combustion/secondary nitrates (29.7%) and soil (5.4%). Local heating units had been pointed out as dominant contributors by long-range transport and ground-wind circulation analyses. Air masses circulating over the Balkan Peninsula denoted regional emissions as responsible for the high concentrations of secondary sulphates. Local and long-range transport analyses combined suggested that the BB and the LC/NO3 originated from the wider urban area. Several Saharan dust episodes were detected as well. Presented results might be a basis for the development of air pollution mitigation strategies in the continental Balkan area, considered one of the most polluted and under-investigated European regions.

Ambient particulate matter source apportionment using receptor modelling in European and Central Asia urban areas

This work presents the results of a PM2.5 source apportionment study conducted in urban background sites from 16 European and Asian countries. For some Eastern Europe and Central Asia cities this was the first time that quantitative information on pollution source contributions to ambient particulate matter (PM) has been performed. More than 2200 filters were sampled and analyzed by X-Ray Fluorescence (XRF), Particle-Induced X-Ray Emission (PIXE), and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to measure the concentrations of chemical elements in fine particles. Samples were also analyzed for the contents of black carbon, elemental carbon, organic carbon, and water-soluble ions. The Positive Matrix Factorization receptor model (EPA PMF 5.0) was used to characterize similarities and heterogeneities in PM2.5 sources and respective contributions in the cities that the number of collected samples exceeded 75. At the end source apportionment was performed in 11 out of the 16 participating cities. Nine major sources were identified to have contributed to PM2.5: biomass burning, secondary sulfates, traffic, fuel oil combustion, industry, coal combustion, soil, salt and “other sources”. From the averages of sources contributions, considering 11 cities 16% of PM2.5 was attributed to biomass burning, 15% to secondary sulfates, 13% to traffic, 12% to soil, 8.0% to fuel oil combustion, 5.5% to coal combustion, 1.9% to salt, 0.8% to industry emissions, 5.1% to “other sources” and 23% to unaccounted mass. Characteristic seasonal patterns were identified for each PM2.5 source. Biomass burning in all cities, coal combustion in Krakow/POL, and oil combustion in Belgrade/SRB and Banja Luka/BIH increased in Winter due to the impact of domestic heating, whereas in most cities secondary sulfates reached higher levels in Summer as a consequence of the enhanced photochemical activity. During high pollution days the largest sources of fine particles were biomass burning, traffic and secondary sulfates.

Evaluation of the Reduction in PM2.5 Concentration During the National Traditional Games of Ethnic Minorities in Zhengzhou

To evaluate the effect of the implementation of emission reduction measures and the improvement in air quality during the National Traditional Games of Ethnic Minorities in Zhengzhou, a series of online instruments were used to continuously observe air pollutants and components of PM2.5 from August 5 to September 30, 2019. Three cases, including before emission reduction (August 5-24), during emission reduction (August 25 to September 18), and after emission reduction (September 19-30), were classified by the implementation of control measures. The results show that the growing concentration of PM2.5 after the cancellation of emission abatement measures (11.7 μg·m-3) was greater than that during the emission reduction (2.3 μg·m-3) compared to the PM2.5 concentration before emission reduction. This thus indicates that the control measures have a significant effect on reducing particulate matter. The main components of PM2.5 were organic matter, nitrate, ammonium, sulfate, and crustal elements. Compared to the proportion of components in PM2.5 before and during the control periods, organic matter and nitrate increased by 3.9% and 0.9%, respectively, while sulfate, ammonium, and crustal elements decreased by 1.1%, 1.9%, and 2.2%, respectively. The results of source appointment by positive matrix factorization show that secondary sulfate, secondary nitrate, secondary organic aerosols, vehicular emissions, industrial emissions, dust, and coal combustion are the main sources of PM2.5. Emission abatement measures reduced the contributions of primary sources such as dust, coal combustion, and industry by 8.3%, 8.2%, and 8.1%, respectively. In contrast, the contributions of secondary organic and nitrate aerosols increased during the control periods, which suggested that the control measures implemented in Zhengzhou had a weaker emission reduction effect on nitrogen oxide and volatile organic compounds than on primary sources of PM2.5.

Characteristics of PM2.5 pollution in Beijing after the improvement of air quality

Following the implementation of the strictest clean air policies to date in Beijing, the physicochemical characteristics and sources of PM2.5 have changed over the past few years. To improve pollution reduction policies and subsequent air quality further, it is necessary to explore the changes in PM2.5 over time. In this study, over one year (2017–2018) field study based on filter sampling (TH-150C; Wuhan Tianhong, China) was conducted in Fengtai District, Beijing, revealed that the annual average PM2.5 concentration (64.8 ± 43.1 μg/m3) was significantly lower than in previous years and the highest PM2.5 concentration occurred in spring (84.4 ± 59.9 μg/m3). Secondary nitrate was the largest source and accounted for 25.7% of the measured PM2.5. Vehicular emission, the second largest source (17.6%), deserves more attention when considering the increase in the number of motor vehicles and its contribution to gaseous pollutants. In addition, the contribution from coal combustion to PM2.5 decreased significantly. During weekends, the contribution from EC and NO3− increased whereas the contributions from SO42−, OM, and trace elements decreased, compared with weekdays. During the period of residential heating, PM2.5 mass decreased by 23.1%, compared with non-heating period, while the contributions from coal combustion and vehicular emission, and related species increased. With the aggravation of pollution, the contribution of vehicular emission and secondary sulfate increased and then decreased, while the contribution of NO3− and secondary nitrate continued to increase, and accounted for 34.0% and 57.5% of the PM2.5 during the heavily polluted days, respectively.

Characterization and Source Apportionment of Fine Particles during a Heavy Pollution Episode over the Yangtze River Delta, China

Regional-scale field observations of fine particles (PM2.5) were carried out at urban, suburban and regional background sites across the Yangtze River Delta (YRD) from 15–30 January 2015. The coefficients of divergence (CD) values reveal the similarity of dataset at the three sites. The PM2.5 concentrations and meteorological data exhibit temporal synchronization. From January 15 to 26, the YRD experienced severe PM2.5 pollution resulting from a cold front moving through and high-pressure control. Then, a 4-day intermittent rain event from 27–30 January significantly scavenged PM2.5. For the chemical components in PM2.5, secondary inorganic ions were dominant, and they accounted for larger proportions at the urban and suburban sites than at the regional background site. The OC/EC ratios were higher in daytime than at night, and were lower on polluted days than on clean (rainy) days. The principal sources of PM2.5 were secondary nitrate (38%) and sulfate (23%) formation, biomass burning (14%), and marine source (8%). Marine (16%) and sulfate (30%) sources were enhanced on clean (rainy) days, indicating the notable effect of marine air masses on PM2.5 chemical components. The open burning source contribution at the regional site was the largest during the polluted period because more air masses arrived from combustion zones.

The Evolution of Pollutant Concentrations in a River Severely Affected by Acid Mine Drainage: Río Tinto (SW Spain)

The Río Tinto, located in the Iberian Pyrite Belt (SW Spain), constitutes an extreme case of pollution by acid mine drainage. Mining in the area dates back to the Copper Age, although large-scale mining of massive sulfide deposits did not start until the second half of the 19th century. Due to acidic mining discharges, the Río Tinto usually maintains a pH close to 2.5 and high concentrations of pollutants along its course. From a detailed sampling during the hydrological year 2017/18, it was observed that most pollutants followed a similar seasonal pattern, with maximum concentrations during autumn due to the washout of secondary soluble sulfate salts and minimum values during large flood events. Nevertheless, As and Pb showed different behavior, with delayed concentration peaks. The dissolved pollutant load throughout the monitored year reached 5000 tons of Fe, 2600 tons of Al, 680 tons of Zn, and so on. While most elements were transported almost exclusively in the dissolved phase, Fe, Pb, Cr, and, above all, As showed high values associated with particulate matter. River water quality data from 1969 to 2019 showed a sharp worsening in 2000, immediately after the mine closure. From 2001 on, an improvement was observed.

Characterization and Source Identification of Elements and Water-Soluble Ions in Submicrometre Aerosols in Brno and Šlapanice (Czech Republic)

Submicrometre aerosol particles (particulate matter, PM1) were collected in two Czech cities (Brno and Šlapanice) during week campaigns in winter and summer of 2009 and 2010. The aerosols were analysed for 14 elements and 12 water-soluble ions using inductively coupled plasma–mass spectrometry and ion chromatography techniques. The average PM1 mass concentration was 14.4 and 20.4 µg m−3 in Brno and Šlapanice, respectively. Most of the analysed elements and ions exhibit distinct seasonal variability with higher concentrations in winter in comparison to summer. The determined elements and ions together accounted for about 29% of total PM1 mass, ranging between 16% and 44%. Ion species were the most abundant components in collected aerosols, accounting for 27.2% of mass of PM1 aerosols, and elements accounted for 1.8% of mass of PM1 aerosols. One-day backward trajectories were calculated using the Hysplit model to analyse air masses transported towards the sampling sites. The Pearson correlation coefficients between individual PM1 components and PM1 mass and air temperature were calculated. To identify the main aerosol sources, factor analysis was applied. Six factors were identified for each locality. The following sources of PM1 particles were identified in Brno: a municipal incinerator, vehicle exhausts, secondary sulphate, a cement factory, industry and biomass burning. The identified sources in Šlapanice were as follows: a combustion source, coal combustion, a cement factory, a municipal incinerator, vehicle exhausts and industry.

Seasonal characterization of aerosol composition and sources in a polluted city in Central China

We characterized the aerosol composition and sources of particulate matter (PM) in Sanmenxia, a polluted city located in the Fen-Wei Plain region of Central China. The PM2.5 concentration decreased by 18% from 72 μg m−3 in 2014 to 59 μg m−3 in 2019. All chemical species presented pronounced seasonal variations, with their highest concentrations in winter due to enhanced emissions and the frequent stagnant meteorological conditions. Nitrate was the major fraction of PM2.5 during all seasons (35–41%) except summer (25%), while sulfate was a dominant species in summer (29%) compared to other seasons (16–18%) from July 2018 to June 2019. The detailed analysis of a wintertime severe haze episode that lasted for approximately half a month demonstrated that secondary aerosols, including secondary organic aerosol, sulfate, nitrate, and ammonium, contributed 89% to non-refractory PM1 (NR-PM1), indicating the remarkable role of secondary aerosol formation in air pollution in Sanmenxia. Positive matrix factorization analysis further showed considerably enhanced low-volatility oxygenated organic aerosol (OA) and hydrocarbon-like OA during severe haze episodes, while significant contributions in semi-volatile oxygenated OA and coal combustion OA during clean periods. Severe pollution events in the city were generally associated with air masses from the southwest, and we also found that aerosol species, especially secondary aerosol species, showed distinct forenoon increases that were caused by the subsidence of air pollutants aloft. Our results highlight that future air quality improvement would benefit substantially from a more efficient control of gaseous precursors, particularly the NOx emissions from industry and vehicle emissions.

Pit Lake and Drinking Water Intake: Example of Coexistence (Middle Urals, Russia)

The dewatering system of the Lipovsky nickel mining pit (Middle Urals, Russia) has performed a dual role. From 1961 to 1991, while nickel was being mined there, it protected the pit from flooding with groundwater; since 1989, it has been the principal source of drinking water for the town of Rezh (≈ 50,000 residents). After mining ceased, water withdrawal from the drainage wells decreased 2.5 times (to 100 L/s), resulting in a 120 m deep pit lake. A mass balance analysis has shown that water from the pit lake has become the leading source of water intake. However, the concentrations of the water’s basic constituents at the eastern edge of the pit are several times higher than at the western edge. The reason for the significant increase in the water withdrawn by the wells of the western intake is the fact, that during the working of the main ore body, the eastern part of the pit was filled with overburden rock and substandard ore with dispersed sulfide mineralization. Flooding of the pit created a single aquifer between the pit lake and the eastern water intake facility, including an artificial aquifer within the refilled part of the pit. The rise of the groundwater level in the artificial aquifer to an elevation above 150 m (after 1994) led to active chemical weathering of sulfide-containing minerals and dissolution of secondary sulfates, which accounts for the increasing levels of constituents in the eastern part of the pit. The artificial aquifer has become a generator of salts. The dumping of sulfidic wastes and subsequent recovery of the water table have led to the release of sulfate, calcium, and metals into the local groundwater. To prevent the formation of an artificial aquifer, it is necessary to either completely remediate the unflooded portion using non-acid generating material or completely inundate the pit. Partial remediation would be the worst scenario as it could destabilize the hydrogeochemical processes and render long-term coexistence of the drinking water intake and the flooded pit problematic.

Source Apportionment of PM2.5 in Florence (Italy) by PMF Analysis of Aerosol Composition Records

An extensive field campaign was carried out in Florence (Tuscany) to investigate the PM2.5 composition and to identify its sources. The scientific objective of this study is providing a reliable source apportionment, which is mandatory for the application of effective mitigation actions. Particulate matter (PM) was collected for one year, simultaneously in a traffic site, in an urban background, and in a regional background site. While the use of two filter types (quartz and Teflon) allowed obtaining a comprehensive chemical characterization (elemental and organic carbon, ions, elements) by the application of different analytical techniques, the location of the three sampling sites allowed getting a better separation among local, urban, regional and transboundary sources. During shorter periods, the aerosol was also collected by means of a streaker sampler and PIXE (Particle Induced X-ray Emission) analysis of these samples allowed the assessment of hourly resolution elemental time trends. Positive matrix factorisation (PMF) identified seven main sources: traffic, biomass burning, secondary sulphate, secondary nitrates, urban dust, Saharan dust and marine aerosol. Traffic mass concentration contributions were found to be strong only at the traffic site (~8 μg·m−3, 33% of PM2.5). Biomass burning turned out to be an important PM2.5 source in Florence (~4 μg·m−3), with very similar weights in both city sites while at the regional background site its weight was negligible. Secondary sulphate is an important PM2.5 source on a regional scale, with comparable values in all three sites (~3.5 μg·m−3). On average, the contribution of the “natural” components (e.g., mineral dust and marine aerosols) to PM2.5 is moderate (~1 μg·m−3) except during Saharan dust intrusions where this contribution is higher (detected simultaneously in all three sites). High-time resolution data confirmed and reinforced these results.

Comparison of Three Receptor Models for Source Apportionment of PM2.5 in Shanghai: Using Hourly Resolved PM2.5 Chemical Composition Data

Continuous measurements of PM2.5 and its chemical composition, including inorganic ions, carbon components, and inorganic elements, were conducted in the urban area of Shanghai from November 2 to 24, 2014. The chemical characteristics and sources of PM2.5 were discussed. The average mass concentration of PM2.5 was (64±33) μg·m-3 (ranging from 12 to 181 μg·m-3). Organic matter contributed the most to the PM2.5 chemical components, accounting for about 28.1% of total PM2.5, followed by NO3-, SO42-, and NH4+, which accounted for 17.4%, 12.4%, and 10.7%, respectively. Meanwhile, three receptor models, including positive matrix factorization (PMF), chemical mass balance (CMB), and multilinear engine 2 (ME2), were applied to apportion the PM2.5 sources based on these online data. The results showed that eight sources were identified, including secondary nitrate, secondary sulfate, secondary organic carbon, heavy fuel oil burning, industry, mobile vehicle exhaust, dust, and power plants. The secondary sources (44.9%-64.8%), including secondary nitrate, secondary sulfate, and secondary organic carbon, were found to be the important contributors to PM2.5. The other two main sources were mobile vehicle exhaust (16.8%-24.8%) and power plants (5.6%-14.9%), whereas other sources were slightly lower contributors. To better verify the accuracy of the PMF, CMB, and ME2 models, the profiles, temporal patterns, and concentrations of different sources obtained by the three models were discussed. Similar source profiles and contributions of secondary nitrate, secondary sulfate, secondary organic carbon, and mobile vehicle exhaust were derived from the PMF, CMB, and ME2, indicating that the results of the three models were reasonable. The ME2 and PMF models simulate better results for power plants and dust sources than CMB, whereas CMB obtained better results for industrial sources.