Organic tracers in fine and coarse aerosols at an urban Mediterranean site: contribution of biomass burning and biogenic emissions

The concentrations of anhydrosugars (levoglucosan, mannosan, and galactosan), polyols (inositol, xylitol, sorbitol, and mannitol), and glucose were measured in PM1 and PM10 samples collected during 1 year at a traffic site in the city of Elche (southeastern Spain). Levoglucosan, mannosan, and galactosan were mainly found in the PM1 fraction since they are mainly emitted from biomass burning (BB). Likewise, inositol, xylitol, and sorbitol were primarily distributed in the fine mode, suggesting a non-negligible contribution from anthropogenic sources (specifically BB) to the levels of these compounds. This was supported by their seasonal variations, with higher concentrations during winter, and their correlations with levoglucosan concentrations. The average contributions of biomass burning and biogenic sources to OC and PM levels were calculated using levoglucosan and mannitol, respectively, as tracers. On average, BB accounted for 12% and 16% of the OC in PM1 and PM10, while the estimated contribution of fungal spores to OC and PM10 levels was 1.2 and 0.8%, respectively. The results of the present study suggest that, at least in the study area, most sugar alcohols are not appropriate tracers of biogenic emissions.

Potential toxic components in size-resolved particles and gas from residential combustion: Emission factor and health risk

Particulate matter (PM) from residential combustion is an existential threat to human health. Emission factors (EFs) of multiple potential toxic components (PTCs) in size-resolved PM and gas from eight residential fuel combustion were measured, and size distribution, gas/particle partitioning and health risks of the PTCs were investigated. Average EFs from clean coal and anthracite coal were PTEs (sum of EFs of 11 Potential Toxic Elements, 6.62 mg/kg fuels) > PAHs (sum of 22 Polycyclic Aromatic Hydrocarbons, 1.12 mg/kg) > OPAHs (sum of 5 Oxygenated Polycyclic Aromatic Hydrocarbons, 0.45 mg/kg) > PAEs (sum of 6 Phthalate Esters, 0.11 mg/kg) > NPAHs (sum of 14 Nitropolycyclic Aromatic Hydrocarbons, 16.84 μg/kg) > OPEs (sum of 7 Organophosphate Esters, 7.57 μg/kg) > PCBs (sum of 6 Polychorinated Biphenyls, 0.07 μg/kg), which were 2-3 and 1-2 orders of magnitude lower than the EFs of PTCs (except PTEs) from bituminous coal and biomass. Most PAHs, OPAHs and NPAHs, which may mainly originate from chemical reactions, showed similar size distributions and averagely 85 % concentrated in PM1. PTEs, PAEs, OPEs and PCBs generated from the release from raw fuels may have a higher proportion, so their size distributions were more complex and varied with combustion temperature, volatility of compounds, binding mode of the raw fuels, and so on. In addition, clean coal and high-quality anthracite coal could reduce the health risks from the potential organic toxic components, but also reveal the stumbling block of PTEs in risk control.

Size-resolved environmentally persistent free radicals in urban road dust and association with transition metals

Environmental persistent free radicals (EPFRs) are receiving growing concerns owing to their potentially adverse impacts on human health. Road dust is one important source of air pollution in most cities and may pose significant health risks. Characteristics of EPFRs in urban road dusts and its formation mechanism(s) are still rarely studied. Here, we evaluated occurrence and size distributions of EPFRs in road dusts from different functional areas of an urban city, and assessed relationship between EPFRs and some transition metals. Strong electron paramagnetic resonance signals of 6.01 × 1016 - 1.3 × 1019 spins/g with the mean g value of 2.0029 ± 0.0019 were observed, indicating that EPFRs consisted of a mixture of C-centered radicals, and C-centered radicals with an adjacent oxygen atom in the urban road dust. Much more EPFRs enriched in finer dust particles. EPFRs significantly correlated with the total Fe, but not water-soluble Fe, suggesting different impacts of water-soluble and insoluble metals in the formation of EFPRs. Health risk assessment results indicated high risk potentials via the ingestion and dermal exposure to EPFRs in road dusts. Future studies are calling to look into formation mechanisms of EPFRs in urban road dusts and to quantitatively evaluate its potential risks on human health.

Measurement of atmospheric nanoparticles: Bridging the gap between gas-phase molecules and larger particles

Atmospheric nanoparticles are crucial components contributing to fine particulate matter (PM_2.5), and therefore have significant effects on visibility, climate, and human health. Due to the unique role of atmospheric nanoparticles during the evolution process from gas-phase molecules to larger particles, a number of sophisticated experimental techniques have been developed and employed for online monitoring and characterization of the physical and chemical properties of atmospheric nanoparticles, helping us to better understand the formation and growth of new particles. In this paper, we firstly review these state-of-the-art techniques for investigating the formation and growth of atmospheric nanoparticles (e.g., the gas-phase precursor species, molecular clusters, physicochemical properties, and chemical composition). Secondly, we present findings from recent field studies on the formation and growth of atmospheric nanoparticles, utilizing several advanced techniques. Furthermore, perspectives are proposed for technique development and improvements in measuring atmospheric nanoparticles.

Fluorescence fingerprinting characteristics of water-soluble organic carbon from size-resolved particles during pollution event

A typical haze pollution process in northern China has necessitated this study which focuses on the fluorescence characteristics of water-soluble organic carbon (WSOC) in size-resolved particles. High concentrations of WSOC were found in both fine (38 μg/m³) and coarse particles (36 μg/m³) during the pollution period, which may be related to the secondary formation of organic aerosols and stable meteorological conditions. Five fluorescent components in WSOC were extracted by parallel factor analysis. Our results showed that the fluorophores in fine and coarse particles were mainly humic-like substances (humic-like, terrestrial humic-like, and high oxidation humic-like substances) and protein-like substances (protein-like and tyrosine-like substances), respectively. Moreover, the aging degree analysis, pollution source tracing, and concentration prediction of WSOC were carried out by fluorescence index. An innovative technique called self-organizing map was proposed for an in-depth investigation of the contamination mechanism of the atmospheric organic aerosol. Furthermore, the difference in the fluorescence characteristics of WSOC in fine particles was higher than that in coarse particles. The atmospheric pollution process increased the degree of difference in fluorescence characteristics. Additionally, an effective method for predicting the size of atmospheric particles was established by combining excitation-emission matrix fluorescence spectroscopy with classification and regression tree analysis.

Inhalable particle-bound marine biotoxins in a coastal atmosphere: Concentration levels, influencing factors and health risks

Characterizing marine biotoxins (MBs) composition in coastal aerosol particles has become essential to tracking sources of atmospheric contaminants and assessing human inhalable exposure risks to air particles. Here, coastal aerosol particles were collected over an almost 3-year period for the analysis of eight representative MBs, including brevetoxin (BTX), okadaic acid (OA), pectenotoxin-2 (PTX-2), domoic acid (DA), tetrodotoxin (TTX), saxitoxin (STX), ciguatoxin (CTX) and ω-Conotoxin. Our data showed that the levels of inhalable airborne marine biotoxins (AMBs) varied greatly among the subcategories and over time. Both in daytime and nighttime, a predominance of coarse-mode AMB particles was found for all the target AMBs. Based on the experimental data, we speculate that an ambient AMB might have multiple sources/production pathways, which include air-sea aerosol production and direct generation and release from toxigenic microalgae/bacteria suspended in surface seawater or air, and different sources may make different contribution. Regardless of the subcategory, the highest deposition efficiency of an individual AMB was found in the head airway region, followed by the alveolar and tracheobronchial regions. This study provides new information about inhalable MBs in the coastal atmosphere. The coexistence of various particle-bound MBs raises concerns about potential health risks from exposure to coastal air particles.

Human health-risk assessment based on chronic exposure to the carbonyl compounds and metals emitted by burning incense at temples

Health effects resulting from the smoke of carbonyl compounds (aldehydes and ketones) and metal-containing incense particles at temples during incense burning periods were evaluated at temple A (without incense reduction activities) and B (with incense reduction activities), Nantou County, in 2018. The predominant size fractions of particles were PM₁, PM_1-2.5, and PM_2.5-10 at both temples. The total particle mass at temple A was approximately 1.1 times that of temple B due to incense reduction at temple B. The most abundant metal elements in all particle size fractions at both temples were Fe, Al, and Zn. Metal species of incense smoke are divided into three groups by hierarchical cluster analysis and heatmaps, showing higher metal contents in groups PM₁, PM_18-10, and PM_18-2.5 at temple A. In contrast, higher metal contents were observed in PM_18-10 and PM_2.5-1 at temple B. Most of the carbonyl species were formaldehyde and acetaldehyde, released during incense burning periods, with concentrations ranging from 6.20 to 13.05 μg/m³ at both temples. The total deposited fluxes of particle-bound metals at temples A and B were determined to be 83.00% and 84.82% using the International Commission on Radiological Protection (ICRP) model. Health-risk assessments revealed that the risk values of metals and carbonyls were above recommended guidelines (10^-6) at temple A. Since worshippers and staff are exposed to incense burning environments with poor ventilation over a long period, these toxic organic compounds and metals increase health risks in the respiratory tract. Therefore, incense reduction is important to achieve healthy temple environments.

Size distributions of source-specific risks of atmospheric heavy metals: An advanced method to quantify source contributions to size-segregated respiratory exposure

Heavy metals in size-segregated particulate matter (PM) were investigated in a Chinese megacity, and an advanced model was developed to quantify source-specific risks focusing on size-segregated respiratory exposure. Incremental lifetime cancer risk (ILCR) and non-cancer risk (hazard quotient: HQ) based on deposition concentrations of heavy metals displayed a peak at 4.7-5.8 µm. The percentage contributions to cancer risk were as follows: industrial emission (IE, 34%) > secondary and transport (ST, 29%) > resuspended dust (RD, 21%) > coal combustion (CC, 11%) > traffic emission (TE, 4%) during spring and summer (SS), and CC (31%) > ST (26%) > IE (21%) > RD (11%) ≈ TE (11%) during autumn and winter (AW). RD (41% of HQ during SS, 28% during AW) and IE (45% of HQ during SS, 35% during AW) dominated non-cancer risk. ILCR and HQ of CC were high at sizes 1.1-2.1 µm and 0.43-0.65 µm; those of RD were high at sizes > 3.3 µm; and those of IE were bimodal at fine (<2.1 µm) and coarse (>2.1 µm) sizes, respectively. Cancer risk was more susceptible to small particles than non-cancer risk, partly because higher ILCR was from CC, but higher HQ was attributed by RD.

Evolution of aerosol chemistry in Xi'an during the spring dust storm periods: Implications for heterogeneous formation of secondary organic aerosols on the dust surface

TSP and 9-stage size-segregated samples were simultaneously collected in Xi'an during the spring of 2013 and analyzed for organic aerosols (OA) on a molecular level. n-Alkanes were the dominant compound class during the whole campaign, followed by fatty acids. High molecular weight (HMW) n-alkanes and fatty acids dominated in the coarse mode particles (>1.1 μm) during the dust event, indicating they were mostly originated from surface soil and plants in the upwind regions. Low-volatile anthropogenic compounds such as benzo(e)pyrene (BeP) and bisphenol A (BPA) dominated in the fine mode particles during the whole campaign. In contrast, semi-volatile anthropogenic compounds such as phenanthrene (Phe) and di-n-butyl phthalates (DBP) showed a bimodal size distribution with a significant increase in the coarse mode during the dust event due to their vaporization from the fine mode particles and the subsequent adsorption on the dust surface. Secondary organic aerosols (SOA) in Xi'an during the dust storm period were predominantly enriched on the coarse particles, which can be ascribed to the adsorption and subsequent oxidation of gas-phase hydrophilic organics on the aqueous-phase of hygroscopic dust surface (e.g., mirabilite). Our work suggested an important role of multiphase reaction in evolution of aerosol chemistry during the dust long-range transport process.

Chemical characteristics of airborne particles in Xi'an, inland China during dust storm episodes: Implications for heterogeneous formation of ammonium nitrate and enhancement of N-deposition

To identify the sources and heterogeneous reactions of sulfate and nitrate with dust in the atmosphere, airborne particles in Xi'an, inland China during the spring of 2017 were collected and measured for chemical compositions, along with a laboratory simulation of the heterogeneous formation of ammonium nitrate on the dust surface. Our results showed that concentrations of Ca²⁺, Na⁺ and Cl^- in the TSP samples were enhanced in the dust events, with the values of 41.8, 5.4 and 4.0 μg m^-3, respectively, while NO₃^- (7.1 μg m^-3) and NH₄⁺ (2.4 μg m^-3) remarkably decreased, compared to those in the non-dust periods. During the dust events, NH₄⁺ correlated only with NO₃^- (R² = 0.52) and abundantly occurred in the coarse mode (>2.1 μm), in contrast to that in the non-dust periods, which well correlated with sulfate and nitrate and enriched in the fine mode (<2.1 μm). SO₄^2- in Xi'an during the dust events existed mostly as gypsum (CaSO₄·2H₂O) and mirabilite (Na₂SO₄·10H₂O) and dominated in the coarse mode, suggesting that they were directly transported from the upwind Gobi Desert region. Our laboratory simulation results showed that during the long-range transport hygroscopic salts in the Gobi dust such as mirabilite can absorb water vapor and form a liquid phase on the particle surface, then gaseous NH₃ and HNO₃ partition into the aqueous phase and form NH₄NO₃, resulting in the strong correlation of NH₄⁺ with NO₃^- and their accumulation on dust particles. The dry deposition flux of total inorganic nitrogen (NH₄⁺ + NO₃^-) in Xi'an during the dust events was 0.97 mg-N m^-2 d^-1 and 37% higher than that in the non-dust periods. Such a significant enhanced N-deposition is ascribed to the heterogeneous formation of NH₄NO₃ on the dust particle surface, which has been ignored and should be included in future model simulations.

Dicarboxylic acids, ω-oxocarboxylic acids, α-dicarbonyls, WSOC, OC, EC, and inorganic ions in wintertime size-segregated aerosols from central India: Sources and formation processes

The size distributions of aerosols can provide evidences for their sources and formation processes in the atmosphere. Size-segregated aerosols (9-sizes) were collected in urban site (Raipur: 21.2°N and 82.3°E) in central India during winter of 2012-2013. The samples were analyzed for dicarboxylic acids (C2-C12), ω-oxocarboxylic acids (ωC2-ωC9), pyruvic acid and α-dicarbonyls (C2-C3) as well as elemental carbon (EC), organic carbon (OC), water-soluble OC (WSOC) and inorganic ions. Diacids showed a predominance of oxalic acid (C2) followed by succinic and azelaic acid whereas ω-oxoacids exhibited a predominance of glyoxylic acid and glyoxal was more abundant than methylglyoxal in all the sizes. Diacids, ω-oxoacids and α-dicarbonyls showed bimodal size distribution with peaks in fine and coarse modes. High correlations of fine mode diacids and related compounds with potassium and levoglucosan suggest that they were presumably due to a substantial contribution of primary emission from biomass burning and secondary production from biomass burning derived precursors. High correlations of C2 with higher carbon number diacids (C3-C9) suggest that they have similar sources and C2 may be produced via the decay of its higher homologous diacids in fine mode. Considerable portions of diacids and related compounds in coarse mode suggest that they were associated with mineral dust particles by their adsorption and photooxidation of anthropogenic and biogenic precursors via heterogeneous reaction on dust surface. This study demonstrates that biomass burning and dust particles are two major factors to control the size distribution of diacids and related compounds in the urban aerosols from central India.

Source apportionment of wide range particle size spectra and black carbon collected at the airport of Venice (Italy)

Atmospheric particles are of high concern due to their toxic properties and effects on climate, and large airports are known as significant sources of particles. This study investigates the contribution of the Airport of Venice (Italy) to black carbon (BC), total particle number concentrations (PNC) and particle number size distributions (PNSD) over a large range (14 nm-20 μm). Continuous measurements were conducted between April and June 2014 at a site located 110 m from the main taxiway and 300 m from the runway. Results revealed no significantly elevated levels of BC and PNC, but exhibited characteristic diurnal profiles. PNSD were then analysed using both k-means cluster analysis and positive matrix factorization. Five clusters were extracted and identified as midday nucleation events, road traffic, aircraft, airport and nighttime pollution. Six factors were apportioned and identified as probable sources according to the size profiles, directional association, diurnal variation, road and airport traffic volumes and their relationships to micrometeorology and common air pollutants. Photochemical nucleation accounted for ∼44% of total number, followed by road + shipping traffic (26%). Airport-related emissions accounted for ∼20% of total PNC and showed a main mode at 80 nm and a second mode beyond the lower limit of the SMPS (<14 nm). The remaining factors accounted for less than 10% of number counts, but were relevant for total volume concentrations: nighttime nitrate, regional pollution and local resuspension. An analysis of BC levels over different wind sectors revealed no especially significant contributions from specific directions associated with the main local sources, but a potentially significant role of diurnal dynamics of the mixing layer on BC levels. The approaches adopted in this study have identified and apportioned the main sources of particles and BC at an international airport located in area affected by a complex emission scenario. The results may underpin measures for improving local and regional air quality, and health impact assessment studies.

Mass distributions and morphological and chemical characterization of urban aerosols in the continental Balkan area (Belgrade)

This work presents characteristics of atmospheric aerosols of urban central Balkans area, using a size-segregated aerosol sampling method, calculation of mass distributions, SEM/EDX characterization, and ICP/MS analysis. Three types of mass distributions were observed: distribution with a pronounced domination of coarse mode, bimodal distribution, and distribution with minimum at 1 μm describing the urban aerosol. SEM/EDX analyses have shown morphological difference and variation in the content of elements in samples. EDX spectra demonstrate that particles generally contain the following elements: Al, Ca, K, Fe, Mg, Ni, K, Si, S. Additionally, the presence of As, Br, Sn, and Zn found in air masses from southeast segment points out the anthropogenic activities most probably from mining activities in southeastern part of Serbia. The ratio Al/Si equivalent to the ratio of desert dust was associated with air masses coming from southeastern and southwestern segments, pointing to influences from North Africa and Middle East desert areas whereas the Al/Si ratio in other samples is significantly lower. In several samples, we found high values of aluminum in the nucleation mode. Samples with low share of crustal elements in the coarse mode are collected when Mediterranean air masses prevailed, while high share in the coarse mode was associated with continental air masses that could be one of the approaches for identification of the aerosol origin. Graphical abstract ᅟ.

Size-resolved aerosol chemical analysis of extreme haze pollution events during early 2013 in urban Beijing, China

Using size-resolved filter sampling and chemical characterization, high concentrations of water-soluble ions, carbonaceous species and heavy metals were found in both fine (PM2.1) and coarse (PM2.1-9) particles in Beijing during haze events in early 2013. Even on clear days, average mass concentration of submicron particles (PM1.1) was several times higher than that previously measured in most of abroad urban areas. A high concentration of particulate matter on haze days weakens the incident solar radiation, which reduces the generation rate of secondary organic carbon in PM1.1. We show that the peak mass concentration of particles shifted from 0.43-0.65μm on clear days to 0.65-1.1μm on lightly polluted days and to 1.1-2.1μm on heavily polluted days. The peak shifts were also found for the following species: organic carbon, elemental carbon, NH4(+), SO4(2-), NO3(-), K, Cu, Zn, Cd and Pb. Our findings demonstrate that secondary inorganic aerosols (36%) and organic matter (26%) dominated the fine particle mass on heavily polluted days, while their contribution reduced to 29% and 18%, respectively, on clear days. Besides fine particles, anthropogenic chemical species also substantially accumulated in the coarse mode, which suggests that particles with aerodynamic diameter larger than 2.1μm cannot be neglected during severe haze events.

Source apportionment of size-segregated atmospheric particles based on the major water-soluble components in Lecce (Italy)

Atmospheric aerosols have potential effects on human health, on the radiation balance, on climate, and on visibility. The understanding of these effects requires detailed knowledge of aerosol composition and size distributions and of how the different sources contribute to particles of different sizes. In this work, aerosol samples were collected using a 10-stage Micro-Orifice Uniform Deposit Impactor (MOUDI). Measurements were taken between February and October 2011 in an urban background site near Lecce (Apulia region, southeast of Italy). Samples were analysed to evaluate the concentrations of water-soluble ions (SO4(2-), NO3(-), NH4(+), Cl(-), Na(+), K(+), Mg(2+) and Ca(2+)) and of water-soluble organic and inorganic carbon. The aerosols were characterised by two modes, an accumulation mode having a mass median diameter (MMD) of 0.35 ± 0.02 μm, representing 51 ± 4% of the aerosols and a coarse mode (MMD=4.5 ± 0.4 μm), representing 49 ± 4% of the aerosols. The data were used to estimate the losses in the impactor by comparison with a low-volume sampler. The average loss in the MOUDI-collected aerosol was 19 ± 2%, and the largest loss was observed for NO3(-) (35 ± 10%). Significant losses were observed for Ca(2+) (16 ± 5%), SO4(2-) (19 ± 5%) and K(+) (10 ± 4%), whereas the losses for Na(+) and Mg(2+) were negligible. Size-segregated source apportionment was performed using Positive Matrix Factorization (PMF), which was applied separately to the coarse (size interval 1-18 μm) and accumulation (size interval 0.056-1 μm) modes. The PMF model was able to reasonably reconstruct the concentration in each size-range. The uncertainties in the source apportionment due to impactor losses were evaluated. In the accumulation mode, it was not possible to distinguish the traffic contribution from other combustion sources. In the coarse mode, it was not possible to efficiently separate nitrate from the contribution of crustal/resuspension origin.