Atmospheric Aerosol Species Research Articles

“Seeing” Beneath the Clouds—Machine‐Learning‐Based Reconstruction of North African Dust Plumes

AbstractMineral dust is one of the most abundant atmospheric aerosol species and has various far‐reaching effects on the climate system and adverse impacts on air quality. Satellite observations can provide spatio‐temporal information on dust emission and transport pathways. However, satellite observations of dust plumes are frequently obscured by clouds. We use a method based on established, machine‐learning‐based image in‐painting techniques to restore the spatial extent of dust plumes for the first time. We train an artificial neural net (ANN) on modern reanalysis data paired with satellite‐derived cloud masks. The trained ANN is applied to cloud‐masked, gray‐scaled images, which were derived from false color images indicating elevated dust plumes in bright magenta. The images were obtained from the Spinning Enhanced Visible and Infrared Imager instrument onboard the Meteosat Second Generation satellite. We find up to 15% of summertime observations in West Africa and 10% of summertime observations in Nubia by satellite images miss dust plumes due to cloud cover. We use the new dust‐plume data to demonstrate a novel approach for validating spatial patterns of the operational forecasts provided by the World Meteorological Organization Dust Regional Center in Barcelona. The comparison elucidates often similar dust plume patterns in the forecasts and the satellite‐based reconstruction, but once trained, the reconstruction is computationally inexpensive. Our proposed reconstruction provides a new opportunity for validating dust aerosol transport in numerical weather models and Earth system models. It can be adapted to other aerosol species and trace gases.

Assessment of Secondary Sulfate Aqueous-Phase Formation Pathways in the Tropical Island City of Haikou: A Chemical Kinetic Perspective.

Sulfate (SO42-) is an essential chemical species in atmospheric aerosols and plays an influential role in their physical-chemical characteristics. The mechanisms of secondary SO42- aerosol have been intensively studied in air-polluted cities. However, few studies have focused on cities with good air quality. One-year PM2.5 samples were collected in the tropical island city of Haikou, and water-soluble inorganic ions, as well as water-soluble Fe and Mn, were analyzed. The results showed that non-sea-salt SO42- (nss-SO42-) was the dominant species of water-soluble inorganic ions, accounting for 40-57% of the total water-soluble inorganic ions in PM2.5 in Haikou. The S(IV)+H2O2 pathway was the main formation pathway for secondary SO42- in wintertime in Haikou, contributing to 57% of secondary SO42- formation. By contrast, 54% of secondary SO42- was produced by the S(IV)+Fe×Mn pathway in summer. In spring and autumn, the S(IV)+H2O2, S(IV)+Fe×Mn, and S(IV)+NO2 pathways contributed equally to secondary SO42- formation. The ionic strength was the controlling parameter for the S(IV)+NO2 pathway, while pH was identified as a key factor that mediates the S(IV)+H2O2 and S(IV)+Fe×Mn pathways to produce secondary SO42-. This study contributes to our understanding of secondary SO42- production under low PM2.5 concentrations but high SO42- percentages.

Field evidence for enhanced generation of reactive oxygen species in atmospheric aerosol containing quinoline components

Organic constituents of atmospheric particular matter (PM) contribute significantly to prompt generation of reactive oxygen species (ROS) in particle phase, which is often quantified in terms of its oxidative potential (OP). In this study, we used complementary methods of the advanced molecular characterization and the OP quantitation to explore potential of different organic species to enhance ROS generation in ambient aerosol samples. We used seven PM2.5 samples collected in the Midwest US, and extracted them sequentially into a set of solvents with different polarity: first non-polar hexane (HEX), then moderately polar dichloromethane (DCM) and finally polar deionized (DI) water. The DI extracts were further separated using solid phase extraction to isolate water-soluble organic carbon (WSOC) from inorganic ions. The OP of obtained extracts was analyzed using dithiothreitol (DTT) assay and reported here in terms of the DTT consumption rate (called DTT activity). The molecular composition of the same extracts was analyzed using a tandem platform of high-performance liquid chromatography (HPLC) coupled with a photodiode array detector (PDA) and a high-resolution mass spectrometer (HRMS). Highest DTT activities were observed in WSOC fractions (>1.1 μM min−1) followed by DCM (0.75–1.1 μM min−1) and HEX (<0.75 μM min−1) fractions, respectively. These results were complemented by the HPLC-PDA-HRMS molecular characterization data indicating numerous redox-active polar organics detected in the WSOC fractions. In particular, chemical component with elemental formula of C11H11N - attributed to dimethyl quinoline (DMQ) - was found systematically across all DTT-active fractions. The unprotonated nitrogen atom in the pyridine ring of quinolines facilitates electron transfer in the redox reactions, catalyzing generation of ROS in the quinoline containing samples. This is the first study that unambiguously identifies quinoline as a promoter of ROS generation determined within complex mixtures of ambient organic aerosols.

Hygroscopicity of organic compounds as a function of organic functionality, water solubility, molecular weight, and oxidation level

Abstract. Aerosol hygroscopicity strongly influences the number size distribution, phase state, optical properties, and multiphase chemistry of aerosol particles. Due to the large number of organic species in atmospheric aerosols, the determination of the hygroscopicity of ambient aerosols remains challenging. In this study, we measured the hygroscopic properties of 23 organics, including carboxylic acids, amino acids, sugars, and alcohols, using a hygroscopicity tandem differential mobility analyzer (HTDMA). Earlier studies have characterized the hygroscopicity either for a limited number of organic compounds using similar techniques or for particles at sizes beyond the microscale range or even bulk samples using other methodologies. Here, we validate these studies and extend the data by measuring the hygroscopicity of a broader suite of organics for particles with sizes under the submicrometer range that are more atmospherically relevant. Moreover, we systematically evaluate the roles of that related physicochemical properties play in organic hygroscopicity. We show that the hygroscopicity of organics varies widely with functional groups and organics with the same carbon number but that more functional groups show higher hygroscopicity. However, some isomers that are very similar in molecular structure show quite different hygroscopicity, demonstrating that other physicochemical properties, such as water solubility, may contribute to their hygroscopicity as well. If the organics are fully dissolved in water (solubility &gt;7×10-1 g mL−1), we found that their hygroscopicity is mainly controlled by their molecular weight. For the organics that are not fully dissolved in water (slightly soluble: 5×10-4 g mL−1 &lt; solubility &lt; 7×10-1 g mL−1), we observed that some of them show no obvious water uptake, which is probably due to the fact that they may not deliquesce under our studied conditions up to 90 % relative humidity (RH). The other type of slightly soluble organic material is moderately hygroscopic, and the larger its solubility is, the higher its hygroscopicity will be. Moreover, the hygroscopicity of organics generally increased with O:C ratios, although this relationship is not linear.

Roles of Sulfur Oxidation Pathways in the Variability in Stable Sulfur Isotopic Composition of Sulfate Aerosols at an Urban Site in Beijing, China

Sulfate (SO42–) is an important chemical species in atmospheric aerosols, which strongly impacts atmospheric chemistry processes and climate change. Stable sulfur isotopes (δ34S) of sulfate aerosol...

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.

Simultaneous determination of nine atmospheric amines and six inorganic ions by non-suppressed ion chromatography using acetonitrile and 18-crown-6 as eluent additive

Atmospheric amines contribute to the nucleation and initial growth of new particles as well as secondary organic aerosol formation, influencing the radiative balance of the Earth's atmosphere. In this study, we develop an ion chromatography (IC) method for separating and quantifying the nine most abundant amines (methylaminium (MMAH+), dimethylaminium (DMAH+), trimethylaminium (TMAH+), ethylaminium (MEAH+), diethylaminium (DEAH+), propylaminium (MPAH+), butylaminium (MBAH+), ethanolaminium (MEOH+), and triethanolaminium (TEOH+)) from six common inorganic species in atmospheric aerosols. The retention times of the amines were altered by the addition of acetonitrile to the eluent because acetonitrile can reduce the adsorption of hydrophobic amines on the stationary phase. The developed method achieved the successful separation of DEAH+ and TMAH+ from inorganic cations, which often coelute with each other in established IC methods. The interference of K+ on the determination of MEAH+ was eliminated by the complexation of K+ with 18-crown-6, which prolonged the retention time of K+. Finally, 9 target amines and 6 common inorganic cations were separated, with a resolution Rs ≥ 1.2 for DEAH+ and MPAH+ and Rs > 1.5 for other species. The detection limits varied in the range of 0.34-1.48 ng for the 9 amines and 0.19-0.56 ng for the inorganic cations. The developed method was successfully applied for the determination of low molecular weight amines and inorganic cations in PM2.5 collected from an urban site in Shanghai and an isolated coast of Chongming Island. Eight amines were detected in the urban samples, in which MMAH+ and DMAH+ dominated. The average amine concentration in the urban aerosols was 76.3 ± 38.4 ng m−3, which is approximately 4-fold higher than those in the marine samples collected from the coast.

Size-resolved characteristics of inorganic ionic species in atmospheric aerosols at a regional background site on the South African Highveld

Aerosols consist of organic and inorganic species, and the composition and concentration of these species depends on their sources, chemical transformation and sinks. In this study an assessment of major inorganic ions determined in three aerosol particle size ranges collected for 1 year at Welgegund in South Africa was conducted. SO42− and ammonium (NH4+) dominated the PM1 size fraction, while SO42− and nitrate (NO3) dominated the PM1–2.5 and PM2.5–10 size fractions. SO42− had the highest contribution in the two smaller size fractions, while NO3− had the highest contribution in the PM2.5–10 size fraction. SO42− and NO3− levels were attributed to the impacts of aged air masses passing over major anthropogenic source regions. Comparison of inorganic ion concentrations to levels thereof within a source region influencing Welgegund, indicated higher levels of most species within the source region. However, the comparative ratio of SO42− was significantly lower due to SO42− being formed distant from SO2 emissions and submicron SO42− having longer atmospheric residencies. The PM at Welgegund was determined to be acidic, mainly due to high concentrations of SO42−. PM1 and PM1–2.5 fractions revealed a seasonal pattern, with higher inorganic ion concentrations measured from May to September. Higher concentrations were attributed to decreased wet removal, more pronounced inversion layers trapping pollutants, and increases in household combustion and wild fires during winter. Back trajectory analysis also revealed higher concentrations of inorganic ionic species corresponding to air mass movements over anthropogenic source regions.

Constrained simulation of aerosol species and sources during pre-monsoon season over the Indian subcontinent

This study was designed to deliver a better concurrence between model estimates and observations, of atmospheric aerosol species, and predict their spatial distribution as consistently as possible. A free running aerosol simulation (freesimu) in a general circulation model (GCM) was performed, and further the simulated aerosol optical depth (AOD) was constrained with the observed AOD. The present study was carried out during the pre-monsoon season and for the Tigerz experiment which was conducted at stations over the Indo-Gangetic plain (IGP) and the Himalayan foot-hills in northern India. Our formulation of the constrained aerosol simulation (constrsimu) was based upon an identification of the freesimu with the most consistent estimates of aerosol characteristic among the three freesimu. The three freesimu (differing in source of emissions and model horizontal resolution) were carried out with the general circulation model (GCM) of Laboratoire de Météorologie Dynamique (LMD-ZT GCM). Black carbon (BC), organic carbon (OC), and sulfate-other water soluble (Sul-ows) estimated from constrsimu amounted to 70%–100% compared to that from freesimu being 20%–50% of their measured counterparts. Among the aerosol species, the pre-monsoon mean concentration of dust was considerably high over most part of the Indian subcontinent; the anthropogenic aerosol species were, however, specifically predominant over the IGP (mostly 8–12 μg m−3 for Sul-ows, OC). The constrsimu estimated total submicron aerosol mass concentration revealed its alarmingly high value over the northern and north-western India (> 100 μg m−3 and as high as 300 μg m−3). While the high value of observed AOD was found being mainly due to dust (AOD due to dust greater than 0.3) over the northern–northwestern IGP, it was due to Sul-ows (AOD due to Sul-ows as high as 0.4) over the eastern IGP, eastern coastline, and the Bay of Bengal. Temporal trend of fine (FM) and coarse mode (CM) AOD from constrsimu estimates and that derived from Tigerz experiment were in phase with each other for most of the days and exhibited a strong positive correlation coefficient. Source of Tigerz aerosols was mainly due to a predominant influence of dust from Africa/west Asia followed by that from northwest India, and of anthropogenic emissions originating in the IGP. A 200% increase was inferred for potential black carbon emissions (using India emission inventory implemented in a GCM) to obtain a concurrence between observed and freesimu BC concentration.

Size-resolved characteristics of inorganic ionic species in atmospheric aerosols at a regional background site on the South African Highveld North-West University's research published in Journal of Atmospheric Chemistry

Size-resolved characteristics of inorganic ionic species in atmospheric aerosols at a regional background site on the South African Highveld North-West University's research published in Journal of Atmospheric Chemistry

Optimization of an ultrasound-assisted derivatization for GC/MS analysis of oxygenated organic species in atmospheric aerosol.

A novel ultrasound-assisted derivatization followed by GC/MS analysis was developed for the quantification of oxygenated organic species in ambient aerosol. Derivatization parameters mostly influencing the analytical response were investigated, i.e., solvent type, reagent concentration, and reaction duration. Response surface methodology was used to design experiments and a quadratic model was utilized to predict the variables and establish the optimal conditions. The study was performed on standard solutions of 30 compounds representing the major classes of oxygenated compounds typically found in ambient aerosol, i.e., low molecular weight carboxylic acids, sugars, and phenols. In comparison with conventional methods, the optimized procedure uses mild reaction temperature (room temperature instead of 70°C), reduces the amount of silyl reagent (24 vs. 40μL), and shortens derivatization times (45 vs. 70min), participating in the current trend of analytical chemistry towards clean, green methods that reduce costs and decrease pollution. Once optimized, the ultrasound procedure was validated by assessing for repeatability, linearity, detection limits, and derivative stability. For all oxygenated organic species, the proposed method showed a good reproducibility-as the relative standard deviations (RSDs%, n=5) of intra-day analysis were ≤7% - a good linearity with the correlation coefficients of calibration curves R 2≥99.8, and low detection limits, ranging from 0.34 to 6.50ngμL-1; thus it is suitable for its applicability in air quality monitoring. Finally, this method was successfully applied to determine 30 oxygenated organic species in three ambient PM2.5 samples collected at an urban site in Northern Italy in three different seasons. Graphical abstract Ultrasound-assisted derivatization is a green alternative method for GC/MS analysis of oxygenated organic species in atmospheric aerosol towards reduction of energy and reactive consumption.

Water Soluble Ionic Species in Atmospheric Aerosols: Concentrations and Sources at Agra in the Indo-Gangetic Plain (IGP)

This study presents a comprehensive set of 2 years of data (January 2009–December 2010) on the chemical composition of ambient aerosols collected at a university campus in Agra, which lies on the Indo-Gangetic Plain (IGP). The average concentration of total suspended particles (TSP) was 213.2 ± 91.4 μg/m 3 . The most abundant ions in TSP were Ca 2+ , NO3 – and SO4 2– , which contributed about 3.2%, 3.1% and 2.7%, respectively. TSP and most of the ions, such as F – , Cl – , NO3 – , SO4 2– , NH4 + and K + , had the highest mass concentrations in winter, while higher mass concentrations of Ca 2+ and Mg 2+ were found in summer. Higher ionic concentrations during the winter season may be attributed to a combined effect of biomass burning and meteorological conditions (low temperature, wind speed and mixing height). The [NO3 – ]/[SO4 2– ] ratio at the present sampling site was 1.1 ± 0.4, which indicates that there were equal contributions from both stationary sources and vehicles. In winter, high [NO3 – ]/[SO4 2– ] ratios (1.7 ± 0.4) could be due to the extensive use of fuelwood and cowdung cakes to combat the cold. The acidity in aerosols is neutralized by the alkaline species, as indicated by the correlation between NO3 – and SO4 2– and sum of (Ca 2+ , Mg 2+ and NH4 + ). Ca 2+ is the major acid neutralizing cation in the aerosols, followed by Mg 2+ and NH4 + . The crustal source contribution was observed based on the ratios of various ions with respect to Ca in soil and aerosol. On the basis of backward trajectories and the associated concentrations of the ions, the aerosol samples were classified into sectors in relation to their origin to determine the related sources. The major sources of water soluble ions identified at Agra are biomass combustion and local soil.

ChemInform Abstract: Ice Nucleation by Particles Immersed in Supercooled Cloud Droplets

AbstractReview: 341 refs.

A practical method for the calculation of liquid–liquid equilibria in multicomponent organic–water–electrolyte systems using physicochemical constraints

Liquid mixtures containing a variety of organic compounds, water, and dissolved electrolytes are prone to liquid–liquid phase separation, owing to non-ideal interactions between water, ions, and organic compounds. Such systems are of practical importance in the design of chemical separation processes as well as the partitioning of semivolatile species in atmospheric aerosols. In this study, a practical phase separation calculation method based on a system of nonlinear equations is presented, applicable to multicomponent systems containing inorganic ions. Expressions are derived that allow consistent use of activity coefficients defined on molality basis for ionic species in combination with mole fraction-based activity coefficients for nonelectrolyte components. Physicochemical considerations are applied together with preliminary evaluation of generated trial compositions to automatically obtain a set of feasible initial guesses. A successive substitution procedure with component-specific step length damping is then employed, followed by a rapid convergence part using a globally convergent solver for systems of nonlinear equations. We discuss several examples that demonstrate the method's remarkable level of reliability even in the case of systems showing highly non-ideal mixing behavior, and we highlight the importance of providing a good initial guess.

Surface tension depression by low-solubility organic material in aqueous aerosol mimics

Surface-active material, including long-chain fatty acids (LCFAs), comprises a significant fraction of organic aerosol mass. Surface-active species are thought to form a film at the gas–aerosol interface, with implications for aerosol heterogeneous chemistry and cloud formation. However, LCFA phase behavior and surface-bulk partitioning has not been characterized under most conditions typical of tropospheric aerosol water (i.e. acidic, high ionic content), making it challenging to predict surface film formation in aerosols. In this study, we present measurements of the surface tension of aqueous solutions containing the slightly soluble LCFAs oleic and stearic acid. The effect of varying pH, organic concentration, and inorganic salt content was tested for each system. We observe surface tension depression compared to water of up to ∼30 and 45% for aqueous solutions containing stearic or oleic acid at pH 0–8 and high inorganic salt concentrations (NaCl and (NH4)2SO4). This suggests that surface film formation is favorable for these species in atmospheric aerosols.

Evidence for 13‐carbon enrichment in oxalic acid via iron catalyzed photolysis in aqueous phase

To investigate the effect of photochemical aging on the stable carbon isotopic ratio (δ13C) of oxalic acid (OxA), a dominant organic species in atmospheric aerosols, we conducted a laboratory photolysis of OxA under H2O2‐Fe3+(Fe2+)‐UV system in aqueous phase and measuredδ13C of remaining OxA. Our results showed that a significant photolysis of OxA occurred with OH radical but the isotopic fractionation of OxA was insignificant. In contrast, in the presence of Fe3+ (Fe2+), we found a significant enrichment of 13C in remaining OxA. We also found that kinetic isotope effect (KIE) of OxA largely depends on photochemical age (irradiation time) and concentration ratios of OxA to iron; 3.20 ± 0.49‰ (2.18 ± 1.18‰) and 21.62 ± 5.41‰ in 90 min and 180 min irradiation, in which OxA and Fe3+ (Fe2+) ratios were 50:1 and 200:1, respectively. The enrichment of 13C in remaining OxA was more significant during the photolysis catalyzed by Fe3+ (7‰) than by Fe2+ (3‰) in 90 min irradiation when OxA and iron ratios are the same (50:1). This study provides a laboratory evidence for the isotopic enrichment of 13C in OxA with photochemical aging. This approach is useful for better interpretation of atmospheric isotopic measurements in terms of the extent of atmospheric processing of aerosols.

Ice nucleation by particles immersed in supercooled cloud droplets

The formation of ice particles in the Earth's atmosphere strongly affects the properties of clouds and their impact on climate. Despite the importance of ice formation in determining the properties of clouds, the Intergovernmental Panel on Climate Change (IPCC, 2007) was unable to assess the impact of atmospheric ice formation in their most recent report because our basic knowledge is insufficient. Part of the problem is the paucity of quantitative information on the ability of various atmospheric aerosol species to initiate ice formation. Here we review and assess the existing quantitative knowledge of ice nucleation by particles immersed within supercooled water droplets. We introduce aerosol species which have been identified in the past as potentially important ice nuclei and address their ice-nucleating ability when immersed in a supercooled droplet. We focus on mineral dusts, biological species (pollen, bacteria, fungal spores and plankton), carbonaceous combustion products and volcanic ash. In order to make a quantitative comparison we first introduce several ways of describing ice nucleation and then summarise the existing information according to the time-independent (singular) approximation. Using this approximation in combination with typical atmospheric loadings, we estimate the importance of ice nucleation by different aerosol types. According to these estimates we find that ice nucleation below about -15 °C is dominated by soot and mineral dusts. Above this temperature the only materials known to nucleate ice are biological, with quantitative data for other materials absent from the literature. We conclude with a summary of the challenges our community faces.

Intercomparison of the measurements of oxalic acid in aerosols by gas chromatography and ion chromatography

Oxalate, the anion of oxalic acid, is one of the most abundant measurable organic species in atmospheric aerosols. Traditionally, this bifunctional species has been measured by gas chromatography (GC) after derivatization to butyl ester and by ion chromatography (IC) without derivatization. However, there are few published comparisons of the two techniques. Here, we report the results of an intercomparison study for the measurement of oxalic acid in Arctic aerosols (< 2.5 µm, n=82) collected in 1992 using GC and IC. The concentrations of oxalic acid by GC ranged from 6.5-59.1 ng m -3 (av. 26.0 ng m -3 , median 26.2 ng m -3 ) whereas those by IC ranged from 6.6-52.1 ng m -3 (av. 26.6 ng m -3 , median 25.4 ng m -3 ). They showed a good correlation (r=0.84) with a slope of 0.96. Thus, observations of oxalate obtained by GC employing dibutyl esters are almost equal to those by IC. Because the accuracy of oxalic acid by GC method largely depends on the method used, it is important to strictly examine the recovery in each study.

Extraction and Determination of Total Bromine, Iodine and Species in Atmospheric Aerosol

Extraction and Determination of Total Bromine, Iodine and Species in Atmospheric Aerosol

Extraction and Determination of Total Bromine, Iodine, and Their Species in Atmospheric Aerosol

The bromine and iodine species in aerosol samples were extracted using ultrapure water ultrasonic method with different extraction time and using pressurizing decomposition with dilute ammonia. The efficiency of the extraction and the stability of bromine and iodine species were compared under different extraction conditions. The results showed that (1) the efficiency of extraction using pressurizing decomposition, which might destroy some unknown form of organic iodine, was relatively higher than those using ultrasonic method; (2) I− was unstable in added standard cellular blank filter during ultrasonic-assisted extraction for long time; and (3) the optimum condition was ultrapure water ultrasonic-assisted extraction for 5 min. Moreover, the suitability of glass microfiber filter (GF) and cellular filter (CF) during extraction for bromine and iodine species in aerosol was also compared, which indicated that GF is favorable for species analysis compared with CF under different kinds of extraction conditions. Based on the extraction results, HPLC-ICPMS approach was developed to analyze bromine and iodine species in atmospheric aerosol. The total iodine, bromine, and their species in the aerosol samples collected from Hefei were then determined accordingly. The levels of total bromine and iodine in Hefei aerosols were 883 and 231 pmol m−3, respectively. Br−was found to be dominant species with 68%, while BrO3− was undetectable. 70% of total iodine occurred as unidentified forms including soluble organic iodine and insoluble iodine.