Water-soluble Ionic Species Research Articles

Long-range transport and source apportionment of marine fine particles in the Taiwan Strait and South China Sea Intersection: Spatiotemporal variations and chemical fingerprints

This study aims to investigate the spatiotemporal variation, chemical characteristics and source apportionment of marine fine particles (PM2.5), and to analyze the transport route towards the intersectional region of the Taiwan Strait and South China Sea. Sampling of PM2.5 was conducted simultaneously at Penghu and Dongsha Islands for 14 consecutive days each quarter from summer 2019 to spring 2020. PM2.5 samples were then returned for conditioning, weighting, and chemical analysis. The chemical mass balance (CMB) receptor model was used to identify the potential PM2.5 sources. It results show that the lowest PM2.5 concentrations were observed in summer, with a gradual increase starting fall, influenced by Asia Northeastern Monsoons (ANMs) transporting particles from the north to Penghu and Dongsha Islands. The most abundant water-soluble ionic species in PM2.5 were SO42−, NO3− and NH4+, catalogued as the secondary inorganic aerosols (SIAs). Meanwhile, the most abundant metals in PM2.5 were crustal elements (Mg, K, Ca, Fe, and Al), while the concentrations of trace metals (V, Cr, Mn, Ni, As, Cd, and Pb), mainly from anthropogenic sources, also increased from fall onwards. Organic carbon (OC) was the main species of carbonaceous content of PM2.5 in all seasons, and OC/EC ratios increased during the seasons with prevailing northeastern winds. Anhydrosugar, concentrations in winter and spring were generally higher than those in summer and fall, indicating significant biomass burning occurring in winter and spring. Correlation analysis showed a high correlation between PM2.5 concentrations and chemical composition between two subtropical islands. The correlation of chemical composition for different transportation routes revealed that northern routes had a higher correction than southern routes. Overall, the cross-boundary PM, accounted for 28.4–61.0% and 36.4–76.8% at Penghu and Dongsha Islands, respectively, significantly impacted local air quality, particularly at Dongsha Islands.

Temporal profile of ionic species and n-alkanes composition of PM10 in a rural environment of Western Himalaya

The temporal profile of PM10 and its composition comprising water-soluble ionic species and n-alkanes studied over the 14 months was segregated into three seasons: winter, summer, and monsoon. The average PM10 concentration exceeds the prescribed National PM10 limits in summer and winter. The PM10 concentration was highest in summer, followed by winter, and lowest in monsoon. Water-soluble inorganic ionic species— major cations (Ca2+, Mg2+, Na+, K+, and NH4+) and anions (F−, Cl−, NO3− and SO42−) contributed an average 30.7% to PM10. The ionic species displayed significant variation, with the highest concentration in winter and the lowest in the monsoon. The secondary inorganic ions, SO42−, NO3−, and NH4+, contributed 84% to the total ionic mass. The ion balance study revealed a strong correlation between anion and cation charge equivalents, suggesting their main contribution to PM10. The neutralization of NO3− + SO42− with NH4+ suggested, NH4+ being the main neutralizing species. n-alkanes concentration in PM10 was significant and showed seasonal variation, highest in the winters and lowest in monsoon. The source profiling of PM10 components, using statistical correlation, regression, and principal component analysis (PCA), revealed solid-fuel biomass, soil dust, and brick kilns and transported materials as major sources.

PM2.5 pollution exceeding Indian standard over a semi-urban region at eastern IGP: Chemistry, meteorological impact, and long-range transport

A year-long study (January–December 2019) on the chemical characterization and meteorological impact on PM2.5 was conducted over a semi-urban station, Shyamnagar, in the easternmost part of the Indo-Gangetic Plains (IGP). PM2.5 concentrations (Mean = 81.69 ± 66.27 μgm−3; 7.10–272.74 μgm−3), the total carbonaceous aerosols (TCA) (Mean = 22.85 ± 24.95 μgm−3; 0.77–102.97 μgm−3) along with differential carbonaceous components like organic carbon (OC) (Mean = 11.28 ± 12.48 μgm−3; 0.48–53.01 μgm−3) and elemental carbon (EC) (Mean = 4.83 ± 5.28 μgm−3; 0.1–22.13 μgm−3) exhibited prominent seasonal variability with the highest concentrations during winter, followed by post-monsoon, pre-monsoon and lowest during monsoon. A similar seasonal variation was observed for the total water-soluble ionic species (Mean = 31.91 ± 20.12 μgm−3; 0.1–126.73 μgm−3). We observed that under the least favorable conditions (low ventilation coefficient), high PM2.5 pollution (exceeding Indian standard) was associated with a high increase in secondary components of PM2.5. Eastern, central and western parts of IGP, as well as Nepal, were the major long-distant source regions whereas the northern part of West Bengal and parts of Bangladesh were the major regional source region for high PM2.5 pollution over Shyamnagar. The ratios like char-EC/soot-EC, non-sea-K+/EC and non-sea-SO42−/EC strongly indicated the dominance of fossil fuel burning over biomass burning. Compared with other studies, we observed that the PM2.5 pollution over this semi-urban region was comparable (and even higher in some cases) with other parts of IGP. The high exceedance of PM2.5 over the Indian standard in Shyamnagar strongly demands an immediate initiation of systematic and regular based air pollution monitoring over semi-urban/non-urban regions in India, especially IGP, in addition to the polluted cities.

Fine aerosol sources at an urban background site in the Eastern Mediterranean (Nicosia; Cyprus): Insights from offline versus online source apportionment comparison for carbonaceous aerosols

A total of 348 daily PM2.5 samples were collected at an urban background site of Nicosia, capital of Cyprus, for one-year period (October 2018–October 2019) to assess the origin and sources of fine PM at the Eastern Mediterranean, a poorly characterized area of the world.The samples were analysed for water soluble ionic species, elemental and organic carbon, carbohydrates and trace metals, the combination of which were utilized to identify pollution sources by applying Positive Matrix Factorization (PMF). Six PM2.5 sources, namely long-range transport (LRT; 38 %), traffic (20 %), biomass burning (16 %), dust (10 %), sea salt (9 %) and heavy oil combustion (7 %), were identified.Despite sampling in an urban agglomeration, the chemical fingerprint of the aerosol is largely dictated by air mass origin rather than local sources. Springtime is characterized by the most elevated particulate levels due to the southerly air masses carrying particles from the Sahara Desert. Northerlies are observed throughout the year but are predominant during summer allowing the LRT source to peak (54 % during summer). Only during winter, due to extensive use of biomass combustion for domestic heating (36.6 % during winter), local sources dominate.A co-located online PMF source apportionment of submicron carbonaceous aerosols (Organic Aerosols, OA; Black Carbon) was performed by the means of an Aerosol Chemical Speciation Monitor (for OA) and an Aethalometer (for BC) for a four-month period. The comparison between the two methodologies allowed to better assess the robustness and limitations of the two methodologies. More specifically, LRT OA and biomass burning BC apportioned by the offline PMF showed a strong consistency with the online apportioned more oxidized oxygenated OA and BCwb, respectively; cross validating these sources. On the other hand, our traffic factor may contain additional hydrocarbon-like OA and BC from fossil fuel sources other than just vehicular emissions. Finally, the offline biomass burning OA source is likely to contain both primary and secondary OA.

Indoor particulate matter (PM2.5) in Malaysian academic building: Elemental characterization and source apportionment

This study aims to determine the elemental compositions of indoor particulate matter (PM2.5) in two selected academic buildings, with emphasis on source apportionment using a multivariate receptor model. PM2.5 samples were collected from lecture halls, laboratories and lecturer offices at the Ministry of Health Training Institute of Sungai Buloh (S1) and the Ministry of Health Training Institute of Sultan Azlan Shah (S2). Sampling took place over 8 h using a low volume sampler (LVS). In this study, various scientific methods such as standard methods for air quality analysis as well as Principal Component Analysis (PCA) and Multiple Linear Regression (MLR) were applied in order to investigate the elemental characterizations and source apportionment of PM2.5, respectively. The PM2.5 compositions for water-soluble ionic species (WSIS) and trace metals were analysed using ion chromatography (IC) and inductively coupled plasma-mass spectrometry (ICP-MS), respectively. Results showed that the mean PM2.5 concentration at S1 (108 ± 39.5 µg m−3) was higher than S2 (91.1 ± 36.6 µg m−3). PCA-MLR analysis revealed that biomass burning (48%) and building material/crustal origin (81%) were the major sources of indoor PM2.5 for S1 and S2, respectively. Modifications and improvements to ventilation systems could be implemented in order to maintain a good health of the building occupants as outside sources may contribute to the presence of pollutants in these buildings.

Variations in the concentration, source activity, and atmospheric processing of PM2.5-associated water-soluble ionic species over Jammu, India.

Concentrations, sources, and atmospheric processing of water-soluble ionic species associated with PM2.5 collected from 2015 to 2017 were studied in Jammu, an urban location in the North-Western Himalayan Region (NWHR).Being ecologically sensitive and sparsely studied for dynamics in PM2.5 and associated WSIS, the present study is important for developing robust air pollution abatement strategies for the air-shed of NWHR. Twenty-four hourly PM2.5 samples were collected on weekly basis at a receptor site and analyzed for WSIS using ion chromatography system. On annual basis, total sum of WSIS (ΣWSIS) contributed about 28.5% of PM2.5, where the contribution of sulfate-nitrate-ammonium, a proxy for secondary inorganic aerosols (SIA), was found to be 18.7% of PM2.5. The ΣWSIS and PM2.5 concentration showed a seasonal cycle with the maximum concentration during winters and the minimum in summers. Mass fraction of ΣWSIS in PM2.5 showed an anti-phase seasonal pattern indicating more source activity during summers. Season-wise, dominant WSIS constituting PM2.5 were NO3-, SO42-, NH4+, and K+ during winters; whereas summer was marked with dominant contributions from SO42-, NH4+, Ca2+, and K+. Seasonal variability exhibited among SIA constituents underscored the crucial role of air temperature and relative humidity regime. It was observed that nss-K+ + NH4+ were sufficient to neutralize most of the acidic species arising from precursor gases (NOx and SOx). Using principal component analysis, five major sources and processes, viz. (a) biomass burning activities, (b) secondary inorganic aerosol formation, (c) input from re-suspended dust, (d) transported dust, and (e) fertilizer residue, were identified for the emissions of PM2.5-associated WSIS over Jammu. In future studies, impacts of dry and/or wet deposition of aerosol-associated WSIS on the crop productivity in the region should be studied.

An Application of Artificial Neural Network to Evaluate the Influence of Weather Conditions on the Variation of PM2.5-Bound Carbonaceous Compositions and Water-Soluble Ionic Species

Previous studies have determined biomass burning as a major source of air pollutants in the ambient air in Thailand. To analyse the impacts of meteorological parameters on the variation of carbonaceous aerosols and water-soluble ionic species (WSIS), numerous statistical models, including a source apportionment analysis with the assistance of principal component analysis (PCA), hierarchical cluster analysis (HCA), and artificial neural networks (ANNs), were employed in this study. A total of 191 sets of PM2.5 samples were collected from the three monitoring stations in Chiang-Mai, Bangkok, and Phuket from July 2020 to June 2021. Hotspot numbers and other meteorological parameters were obtained using NOAA-20 weather satellites coupled with the Global Land Data Assimilation System. Although PCA revealed that crop residue burning and wildfires are the two main sources of PM2.5, ANNs highlighted the importance of wet deposition as the main depletion mechanism of particulate WSIS and carbonaceous aerosols. Additionally, Mg2+ and Ca2+ were deeply connected with albedo, plausibly owing to their strong hygroscopicity as the CCNs responsible for cloud formation.

Emission factors of PM2.5-Bounded selected metals, organic carbon, elemental carbon, and water-soluble ionic species emitted from combustions of biomass materials for source Apportionment—A new database for 17 plant species

Over the past few years, burning agricultural or crop residues has resulted in serious air pollution, particularly in northern Thailand. In this study, constant endeavours were made to achieve the first-hand emission factors (EFs) of water-soluble ionic species (WSIS), organic carbon, elemental carbon, and selected metals emitted from the combustion of 17 plant species. The average EF values of organic carbon (OC) and elemental carbon (EC) ranged from 280 g kg−1 to 1441 g kg−1 and from 32 g kg−1 to 142 g kg−1, respectively. Sugarcane burning shows the highest EFs of toxic metals, such as V, Cr, Co, Ni, and Pb, which is concerning because Thailand is the world's second largest sugar exporter. The comparatively high percentage contribution of Cl− coupled with extremely low levels of K+ resulted in questions on its reliability as a chemical tracer for maritime aerosols and biomass burning particles, respectively. OC/EC ratios varied from 4.68 (Leucaena leucocephala) to 11.4 (Terminalia catappa) with the average value of 8.88 ± 1.72. Further attempts to investigate the most suitable diagnostic binary ratios of metals representing biomass burning were conducted using 2D plots of Zn/Mn, Fe/Zn, Fe/Cu, Ni/Co, Mn/Cr, Ni/V, Al/Si, and Pb/As. In this study, Mn/Cr versus Ni/V and Pb/As versus Al/Si can be used as diagnostic binary ratios to classify biomass-burning-related aerosols.

Understanding the Sources of Ambient Fine Particulate Matter (PM2.5) in Jeddah, Saudi Arabia

Urban air pollution is rapidly becoming a major environmental problem of public concern in several developing countries of the world. Jeddah, the second-largest city in Saudi Arabia, is subject to high air pollution that has severe implications for the health of the exposed population. Fine particulate matter (PM2.5) samples were collected for 24 h daily, during a 1-year campaign from 2013 to 2014. This study presents a detailed investigation of PM2.5 mass, chemical composition, and sources covering all four seasons of the year. Samples were analyzed for black carbon (BC), trace elements (TEs), and water-soluble ionic species (IS). The chemical compositions were statistically examined, and the temporal and seasonal patterns were characterized using descriptive analysis, correlation matrices, and elemental enrichment factor (EF). Source apportionment and source locations were performed on PM2.5 samples using the positive matrix factorization (PMF) model, elemental enrichment factor, and air-mass back trajectory analysis. The 24-h mean PM2.5 and BC concentrations ranged from 33.9 ± 9.1–58.8 ± 25 µg/m3 and 1.8 ± 0.4–2.4 ± 0.6 µg/m3, respectively. Atmospheric PM2.5 concentrations were well above the 24-h WHO guideline of 15 µg/m3, with overall results showing significant temporal and seasonal variability. EF defined two broad categories of TEs: anthropogenic (Ni, V, Cu, Zn, Cl, Pb, S, Lu, and Br), and earth-crust derived (Al, Si, Mg, K, Ca, Ti, Cr, Mn, Fe, and Sr). The five identified factors resulting from PMF were (1) fossil-fuels/oil combustion (45.3%), (2) vehicular emissions (19.1%), (3) soil/dust resuspension (15.6%), (4) industrial mixed dust (13.5%), and (5) sea-spray (6.5%). This study highlights the importance of focusing control strategies, not only on reducing PM concentration but also on the reduction of components of the PM as well, to effectively protect human health and the environment.

Particulate Matter Ionic and Elemental Composition during the Winter Season: A Comparative Study among Rural, Urban and Remote Sites in Southern Italy

We present an overview of the concentrations and distributions of water-soluble ion species and elemental components in ambient particulate matter for five measurement sites in southern Italy with the aim of investigating the influence of the different site characteristics on PM levels. The sites encompass different characteristics, ranging from urban to coastal and high-altitude remote areas. PM10 and PM2.5 fractions were collected simultaneously using dual channel samplers during the winter period from November 2015 to January 2016 and analyzed for water-soluble ion species, using ion chromatography, and elemental composition, using inductively coupled plasma mass spectrometry (ICP-MS). In all sites, PM2.5 represented the higher contribution to particulate mass, usually more than two times that of the coarse fraction (PM2.5−10). At the coastal site in Capo Granitola (Western Sicily), sea salts constituted about 30% of total PM10 mass. On average, ion species accounted for 30% to 60% of total PM10 mass and 15% to 50% of PM2.5 mass. We found that secondary ion species, i.e., SO42−, NO3− and NH4+ dominated the identifiable components within both PM2.5 and PM10 fractions. The chlorine–sodium ratio was usually lower than that expected from the natural level in sea salt, evidencing aged air masses. At the monitoring site in Naples, a highly urbanized area affected by high levels of anthropogenic source emissions, an increased contribution of ammonium was found, which was imputed to the increased ammonia emissions from industrial combustion sources and road traffic. The concentrations of the investigated elements showed noteworthy differences from one site to another. The PM10 fraction was highly enriched by sources of anthropogenic origin in the samples from the most urbanized areas. In general, the enrichment factors of the elements were similar between the PM10 and PM2.5 fractions, confirming common sources for all elements.

Chemical properties of emissions from solid residential fuels used for energy in the rural sector of the southern region of India.

In the present study, we have estimated the emission factors (EFs) of particulate matter (PM), organic and elemental carbon (OC and EC), oxide of sulfur and nitrogen, and water-soluble ionic species emitted from residential fuels (fuelwood, crop residue, dung cake) used in the rural sector of five states (Kerala, Karnataka, Andhra Pradesh, Telangana, Tamil Nadu) of the southern region of India. Average EFs of PM, OC, and EC from fuelwood (FW), crop residues (CR), and dung cakes (DC) from southern region of India are estimated as follows: PM: 6.35 ± 5.64g/kg (FW), 6.99 ± 5.46g/kg (CR), 9.69 ± 3.73g/kg (DC); OC: 1.60 ± 1.72g/kg (FW), 1.50 ± 1.52g/kg (CR), 3.54 ± 0.75g/kg (DC); and EC: 0.46 ± 0.53g/kg (FW), 0.29 ± 0.17g/kg (CR), 0.21 ± 0.11g/kg (DC), respectively. Similarly, the average EFs of SO2, NOx from FW, CR, and DC are determined to be as follows: SO2: 0.40 ± 0.37g/kg (FW), 1.17 ± 0.25g/kg (CR), and 0.18 ± 0.10g/kg (DC); NOx: 1.11 ± 1.22g/kg (FW), 0.69 ± 0.37g/kg (CR), and 0.91 ± 0.54g/kg (DC), respectively. PO43- shows the highest EF from FW (646.02 ± 576.35mg/kg), CR (531.06 ± 678.29mg/kg) among all anions followed by Cl- (FW: 512.91 ± 700.35mg/kg, CR: 661.61 ± 865.46mg/kg and DC: 104.16 ± 54.01mg/kg); whereas, Na+ shows highest EF from FW (254.05 ± 298.50mg/kg) and CR (249.36 ± 294.85mg/kg) among all cations. The total emissions of trace gases, PM, and their chemical composition from FW, CR, and DC have been calculated using laboratory-generated EFs over the southern region of India. CR (1595.58 ± 14.24 Gg) contributes to higher emission of PM as compared to FW (218.78 ± 53.93 Gg), whereas the contribution from DC is negligible.

Effect of forest floor fuel moisture content on chemical components of PM2.5 emitted during combustion

The moisture content of forest floor fuels changes continuously with the influence of environmental factors; thus it has an important impact on the concentration and chemical composition of particulate matter emitted during forest fire. However, most previous studies quantify emissions of particulate matter and constituents using dry samples. In this study, we use a self-designed semi closed combustion simulator to quantify emission of total carbon (TC), organic carbon (OC), elemental carbon (EC) and water-soluble ions in fine particulate matter (PM2.5) using fuels of four tree species that differ in moisture content (0, 10, 20 and 30%). The results showed that the emissions of TC, OC and EC and total water-soluble inorganic ions increased significantly (<0.05) with increasing moisture content of fuels, and fuels of coniferous species emitted significantly more pollutants than fuels of broadleaved species. Similarly combustion of leaf samples emitted more carbonaceous components and water-soluble ions than combustion of branches. K+, NH4+ and Cl− were the main components of water-soluble ionic species, and emissions of K+, Ca2+, Na+, Mg2+, NH4+, Cl−, Br−, NO3−, NO2−, SO42− increased with increasing moisture content of fuels. Fuel moisture content had a great impact on the inorganic salt composition in the particulate matter emitted during combustion. The findings have an important implication on the use of prescribed early fire as management tools as the moisture content of the fuels early during the dry season is still high.

An application of aromatic compounds as alternative tracers of tsunami backwash deposits

This manuscript provides some comprehensive technical insights regarding the application of polycyclic aromatic hydrocarbons (PAHs) characterized by using Gas-Chromatography Mass Spectrometry. Although numerous chemical species such as water soluble ionic species (e.g. Na+, K+, Cl−, Ca2+, Mg2+) and acid leachable heavy metal fractions (e.g. Fe, Cd, Al, Mo, Sb, As, Cu, Zn, Pb, and Mn) can be used to characterize tsunami deposits, the knowledge of PAH congeners as alternative chemical species for identifying tsunami backwash deposits is strictly limited. This manuscript is exclusive because it aims to find some alternative chemical proxies in order to distinguish tsunami backwash deposits from typical marine sediments. A wide range of diagnostic binary ratios of PAH congeners have been selected in order to characterize Typical Marine Sediments (TMS), Tsunami backwash deposits (TBD), Onshore Tsunami Deposits (OTD) and Coastal Zone Soils (CZS). The state of the art and future perspectives coupled with both advantages and disadvantages of above mentioned chemical tracers will be critically reviewed and further discussed.

Impact assessment of continental and marine air-mass on size-resolved aerosol chemical composition over coastal atmosphere: Significant organic contribution in coarse mode fraction

Size-segregated aerosols (five stages from <1.1 to >7 μm in diameter) collected from a coastal location in south-west peninsular India were analysed for water-soluble ionic species, carbonaceous aerosols and metallic species on a seasonal basis for two years (2017–19). The annual mean concentration of the components Na+, Ca2+, Mg2+, Cl−, NO3−, Al, Fe exhibited coarse mode (> 2 μm) enhancement; while NH4+, K+, SO42−, MSA−, oxalate, Organic carbon (OC), Elemental carbon (EC) peaked in fine mode (< 2 μm). The contribution of fine mode aerosols dominated under the influence of continental air-mass and a relative shift towards coarse mode size regime with respect to marine air-mass was observed. The relative contribution of analysed species showed the dominance of sea-salt fraction in coarse mode during monsoon, anthropogenic ions in fine mode during post-monsoon, crustal species in coarse mode during pre-monsoon and carbonaceous species in fine mode during winter. While nss-SO42− was found to be a major component of fine mode aerosol fraction, OC contributed significantly for both coarse and fine mode. Distinct seasonal variation in OC size-distribution was observed. Fine mode OC dominated during post-monsoon and winter while coarse mode OC peaked during pre-monsoon and monsoon, indicating its multiple sources and formation pathways. The water-soluble fraction of OC predominantly existed in fine mode and was modulated by changing synoptic air-masses. The water insoluble OC fraction was found to be modified by sea-land breeze activities and exhibited coarse mode nature. The significant contribution of OC in coarse mode size regime over this coastal atmosphere has been attributed to; the condensation of gaseous precursors on pre-existing coarse particles leading to the formation of coarse mode WSOC and the primary emission from natural terrestrial and marine organic matter resulting in the emission of coarse mode WIOC.

Water-soluble ionic species in atmospheric aerosols over Dhauladhar region of North-Western Himalaya.

Water-soluble ionic species (WSIS) have been used as potential markers for different source(s) and underlining process(es) emitting and transforming atmospheric aerosols. PM10 aerosol sampling was performed once in a week for a complete one year, at a mid-altitude urban and a low-altitude rural location simultaneously in the Dhauladhar region of the North-Western Himalaya. Aerosol samples were analysed for major WSIS (anions: F-, Cl-, NO3-, PO43- and SO42-; cations: Na+, NH4+, K+, Ca2+ and Mg2+) using the ion chromatography system. Results showed that WSIS constitutes around 15% of PM10 aerosol load in the region. SO42- contributes the maximum (~ 50%) followed by NO3- (~ 12.5%) and NH4+ (~ 12.5%) to the total concentration of WSIS analysed. During all the seasons, average concentrations of PM10 and associated WSIS were observed to be higher over the rural location in comparison to the urban location. The total concentration of WSIS was found to be maximum during the winter season. Principal component analysis performed on the WSIS concentration dataset revealed four major sources of PM10-associated WSIS viz. re-suspension of soil or local sediments; conversion of pollutant gases (SOx, NOx and NH3) to particles, i.e., secondary inorganic aerosol formation; evaporative loss or re-suspension of inorganic (NPK) fertilizers' residues and biomass/crop-residue burning emissions in the Dhauladhar region of the North-Western Himalaya.

Impacts of PM2.5 sources on variations in particulate chemical compounds in ambient air of Bangkok, Thailand

In this study, PM2.5-bound carbonaceous compounds, including organic carbon (OC), elemental carbon (EC), water-soluble ionic species (WSIS), and polycyclic aromatic hydrocarbons (PAHs) in the ambient air of Bangkok were analysed. The mean PM2.5 concentration was 77.0 ± 21.2 μg m−3, while the average concentrations of OC, and EC were 8.03 ± 4.02, and 2.62 ± 1.49 μg m−3, respectively. The relatively high OC/EC ratio (3.52 ± 1.41) coupled with a strong positive correlation between K+ and carbonaceous compounds (K+vs. OC (r = 0.86), K+vs. EC (r = 0.87), K+vs. Char-EC (r = 0.82)) suggest that biomass burning are one of the major contributors to PM2.5 in the sampling area. A comparatively high abundance of both B[g,h,i]P and Ind guides that vehicular exhausts, industrial combustion, and burning of waste might reflect the sources of these PAHs in Bangkok's atmosphere. Interestingly, hierarchical cluster analysis (HCA) indicated that the main source of PM2.5 was a mixture of various combustion activities (e.g. biomass burning, vehicular exhaust, fossil fuel, coal, and industrial emissions). Principal Component Analysis (PCA) successfully classified five principal sources of PM2.5, including vehicular exhaust, biomass burning, sea salt aerosol, power plant, and industrial emissions, which accounted for 43.7%, 24.0%, 10.5%, 6.48%, and 4.46%, respectively. These results indicated that the effects of vehicular exhausts and biomass burning played an important role in governing the PM2.5 level in ambient air of Bangkok. The findings of this study aid policymakers in launching effective air quality control strategies based on the source apportionment analysis.

Source apportionment and health risk assessment of airborne particulates over central Indo-Gangetic Plain

Sources of airborne particulates (PM10) were investigated in two contrasting sites over central Indo-Gangetic Plain (IGP), one representing a rural background (Mirzapur) and another as an urban pollution hotspot (Varanasi). Very high PM10 concentration was noted both in Varanasi (178 ± 105 μgm−3; N:435) and Mirzapur (131 ± 56 μgm−3; N:169) with 72% and 62% of monitoring days exceeded the national air quality standard, respectively. Particulate-bound elements contribute significant proportion of PM10 mass (15%–18%), with highest contribution from Ca (7%–10%) and Fe (2%–3%). Besides, presence of Zn (1%–3%), K (1%–2%) and Na (1%–2%) was also noted. Water-soluble ionic species contributed 15%–19% of particulate mass, primarily by the secondary inorganic aerosols (SIA). Among the SIA, sulphate (5%–7%) and nitrate (4%) were prominent, contributing 59%–62% of the total ionic load, especially in winter. Particulate-bound metallic species and ions were selectively used as signatory molecules and source apportionment of PM10 was done by multivariate factor analysis. UNMIX was able to extract particulate sources in both the locations and crustal resuspensions (dust/-soil) were identified as the dominant source contributing 57%–63% of PM10 mass. Secondary aerosols were the second important source (17%–23%), followed by emissions from biomass/-refuse burning (10–19%). Transport of airborne particulates from upper IGP by prevailing westerly were identified as the important contributor of particulates, especially during high particulate loading days. Health risks associated to particulate-bound toxic metal exposure were also assessed. Non-carcinogenic health risk was within the permissible limit while there is possibility of elevated risk for PM10-bound Cr and Cd, if adequate control measures are not in place.

Seasonal variation and secondary formation of size-segregated aerosol water-soluble inorganic ions in a coast megacity of North China Plain

The aerosol samples of water-soluble inorganic ions (WSIs), including SO42-, NO3-, NH4+, Cl-, K+, Na+, Ca2+, and Mg2+ in size-segregated particulate matter (PM), were collected by an Anderson sampler (with 8 nominal cut-sizes ranged from 0.43 to 9.0 μm) in urban Tianjin during 2013-2014. The results showed that particulate matters in the fine mode (PM2.1, Dp < 2.1 μm) comprised large part of mass concentrations of aerosols, and the water-soluble ionic species in the fine mode were 47.07 ± 14.29 μg m-3 (spring), 67.87 ± 28.74 μg m-3 (summer), 86.60 ± 48.53 μg m-3 (autumn), and 104.16 ± 51.76 μg m-3 (winter), respectively, which accounted for 59.5%, 63.3%, 71.9%, and 71.4% of the PM2.1 mass concentrations. Secondary pollutants of SO42-, NO3-, and NH4+ (SNA) were the dominant contributors of WSIs, which showed a bimodal size distribution in each season, with the larger peak appeared in the size fraction of 0.65-1.1 μm and the smaller one in 3.3-5.8 μm fraction. SNA concentrations in lightly polluted days (LPD) and heavily polluted days (HPD) were observably higher than non-polluted days (NPD), especially in the fine mode, with the peak diameter moving from 0.43-0.65 μm on NPD to 0.65-1.1 μm on LPD and HPD. The correlation analysis between NH4+, NO3-, and SO42- suggested that almost all SO42- and NO3- for fine particles had been completely neutralized by NH4+, and primarily existed in the forms of (NH4)2SO4 and NH4NO3. The sulfur oxidation ratio (SOR) and nitrogen oxidation ratio (NOR) on LPD and HPD in fine mode were observably higher than those on NPD, especially in the range of 0.65-1.1 μm and 1.1-2.1 μm. Furthermore, SOR and NOR values in the size fraction of 0.43-3.3 μm increase as the RH elevated, especially in 0.43-2.1 μm, where RH was significantly positive correlated with SOR and NOR, indicating the significant contributions of heterogeneous processes to the secondary formation of SO42- and NO3-. These results suggested an enhanced formation ability of secondary pollutants under high RH in the coast city. Therefore, controlling the precursors of SNA, such as SO2 and NOx, would be more effective to reduce the fine particulate pollution in the coast megacity of Tianjin.

Assessing atmospheric dry deposition via water-soluble ionic composition of roadside leaves

This study focuses on the water-soluble ion concentrations in the washing solution of leaves of different roadside tree species at three sites in Iran to estimate the ionic composition of the dry deposition of ambient air particulates. All considered water-soluble ion concentrations were significantly higher next to the roads with high traffic density compared to the reference site with low traffic density. The PCA results showed that Ca2+, Mg2+, and originated mainly from traffic activities and geological sources, and Na+, Cl−, K+ and F− from sea salts. In addition to sea salt, K+ and F− were also originated from anthropogenic sources i.e. industrial activities, biomass burning and fluorite mining. Moreover, the concentration of the water-soluble ions depended on species and site. C. lawsoniana had significantly higher ion concentrations in its leaf washing solution compared to L. japonicum and P. brutia which indicates C. lawsoniana is the most suitable species for accumulating of atmospheric dry deposition. From our results, it can be concluded that sites with similar traffic density can have different particle loads and water-soluble ion species, and that concentrations in leaf-washing solutions depend on site conditions and species-specific leaf surface characteristics.

Effects of Agricultural Waste Burning on PM2.5-Bound Polycyclic Aromatic Hydrocarbons, Carbonaceous Compositions, and Water-Soluble Ionic Species in the Ambient Air of Chiang-Mai, Thailand

PM2.5 is widely regarded as a major air pollutant due to its adverse health impacts and intimate relationship with the climate system. This study aims to characterize the chemical components (e.g., organic carbon (OC), elemental carbon (EC), water soluble ionic species (WSIS) and polycyclic aromatic hydrocarbons (PAHs) in PM2.5 collected at Doi–Inthanon in Chiang-Mai, Thailand, the highest mountain in Thailand. All samples (n = 50) were collected by MiniVolTM portable air samplers from March 2017 to March 2018. In this study we found the average PM2.5 concentration was 100 ± 48.6 μg m−3. The OC/EC ratio was 6.8 ± 3.0, and the decreasing order of the WSIS concentrations was SO4 2->Na+>Ca2+>NH4 +>NO3 ->K+>Cl−>NO2 ->Mg2+> F-. The total concentrations of nineteen PAHs were defined as the sum of Ace, Fl, Phe, Ant, Fluo, Pyr, B[a]A, Chry, B[b]F, B[k]F, B[a]F, B[e]P, B[a]P, Per, Ind, B[g,h,i]P, D[a,h]A, Cor, and D[a,e]P. The concentration of total PAHs was 2.361 ± 2.154 µg m−3. Principal component analysis (PCA) highlights the importance of vehicular exhaust, biomass burning, diesel emissions, sea-salt aerosols and volatilization from fertilizers as the five dominant potential sources that accounted for 51.6%, 16.2%, 10.6%, 5.20% and 3.70% of the total variance, respectively. The rest of the 12.7% variance probably is associated with unidentified local and regional sources such as incinerators, joss paper/incense burning, and domestic cooking. Interestingly, the results from the source estimations from the PCA underlined the importance of vehicular exhaust as the major contributor to the PM2.5 concentrations in the ambient air of Don-Inthanon, Chiang-Mai province. However, it is crucial to emphasize that the impacts of agricultural waste burning, fossil fuel combustion, coal combustion and forest fires on the variations of OC, EC and WSIS contents were not negligible.