Gas-particle Partition Coefficient Research Articles

Characterization and health risks of short- and medium-chain chlorinated paraffins in the gas and size-fractionated particulate phases in ambient air

Short-chain and medium-chain chlorinated paraffins (SCCPs and MCCPs) have garnered significant attention because they have persistence and potential toxicity, and can undergo long-distance transport. Chlorinated paraffins (CPs) inhaled in the size-fractionated particulate phase and gas phase can carry different risks to human health due to their ability to accumulate in different regions of the respiratory tract and exhibit varying deposition efficiencies. In our study, large-volume ambient air samples in both the size-fractionated particulate phase (Dp < 1.0 μm, 1.0–2.5 μm, 2.5–10 μm, and Dp ≥ 10 μm) and gas phase were collected simultaneously in Beijing using an active sampler. The overall levels of SCCPs and MCCPs were relatively high, the ranges being 57–881 and 30–385 ng/m3, respectively. SCCPs tended to be partitioned in the gas phase (on average 75% of the ΣSCCP concentration), while MCCPs tended to be partitioned in the particulate phase (on average 62% of the ΣMCCP concentration). Significant correlations were discovered between the logarithm-transformed gas–particle partition coefficients (KP) and predicted subcooled vapor pressures (PL0) (p < 0.01 for SCCPs and MCCPs) and between the logarithm-transformed KP values and octanol–air partition coefficients (KOA) (p < 0.01 for SCCPs and MCCPs). Thus, the slopes indicated that organic matter absorption was the dominant process involved in gas–particle partitioning. We used the ICRP model to calculate deposition concentrations for particulate-associated CPs in head airways region (15.6–71.4 ng/m³), tracheobronchial region (0.8–4.8 ng/m³), and alveolar region (5.1–21.9 ng/m³), then combined these concentrations with the CP concentrations in the gas phase to calculate estimated daily intakes (EDIs) for inhalation. The EDIs for SCCPs and MCCPs through inhalation of ambient air for the all-ages group were 67.5–184.2 ng/kg/day and 19.7–53.7 ng/kg/day, respectively. The results indicated that SCCPs and MCCPs in ambient air do not currently pose strong risks to human health in the study area.

Evidences for the influence from key chemical structures of per- and polyfluoroalkyl substances on their environmental behaviors

This study carried out the atmospheric and precipitation observation in Beijing for nearly one year, and firstly simultaneously observed the pollution characteristics of PFASs and their main isomers, focusing on their gas-particle partitioning mechanism and dry and wet deposition characteristics. After deducting PFASs in the aqueous phase of particulate matter, the gas-particle partitioning coefficients (−7.04 to −5.49) were about 3–4 units smaller than before (−2.77 to −1.51), and all were smaller than 0, which indicated that each PFAS and isomer were more distributed in the gas phase. Dry deposition was dominant in the atmospheric deposition of each PFAS and isomer with relative contribution of 66 ± 17%, but the relative contribution of dry deposition was significantly different. It was found that the gas-particle partitioning coefficient can be influenced by key chemical structures such as carbon chain length, functional group type, and isomer structure. Furthermore, the gas-particle partitioning can influence the dry and wet deposition of PFASs. Specifically, PFASs with longer carbon chains, carboxylic acid functional group (compared to sulfonic acid functional group) or PFOA branched chain structures had larger gas-particle partitioning coefficients and can be more distributed in the hydrophobic phase of particulate matter, and their relative contributions of dry deposition were smaller.

Sources, gas-particle distribution and health risks of atmospheric PAHs in two typical basin cities in China

The sources of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere of various cities are highly intricate. Conducting research on the pollution characteristics of different types of PAHs in cities will help to focus on solving air pollution problems based on urban characteristics. Polycyclic aromatic hydrocarbons (PAHs) in the PM2.5-bound state and gas-phase were analyzed in the winter atmosphere of Yuncheng and Nanyang, China, to determine their pollution and spatial characteristics. The results revealed that in Yuncheng, the average concentrations of these 16 PAHs were 129.83 ± 96.63 ng m−3 in the PM2.5-bound form and 168.05 ± 88.64 ng m−3 in the gas phase, surpassing those observed in Nanyang, where the averages were 66.53 ± 32.49 ng m−3 and 112.80 ± 65.90 ng m−3 for particulate and gas phases, respectively. Gaseous samples primarily contained low molecular weight PAHs, while medium and high molecular weight PAHs were more prevalent in particulate samples. The linear relationship between the gas-particle partition coefficient (logKP) and the gas partition coefficient (PL0) and KOA value of PAHs in both cities suggested that during winter, PAHs in Yuncheng and Nanyang predominantly adsorb onto particles, failing to achieve gas-particle equilibrium. Source analysis using positive matrix factorization (PMF) identified coal combustion (26.4%–41.9%), biomass combustion (26.3%–29.6%), motor vehicle emissions (16.3%–30.4%), and evaporation sources (15.8%–26.9%) as the primary sources of atmospheric PAHs in both cities. Potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) analyses indicated that pollutants originating from the northwest direction and near-earth air masses exerted a substantial influence on both cities. According to health risk assessments, both Yuncheng City and Nanyang City exhibited a certain risk of cancer due to atmospheric PAH exposure. However, the risk of cancer was higher in Yuncheng City compared to Nanyang City. The research results uncover the pollution characteristics and primary sources of polycyclic aromatic hydrocarbons (PAHs) in different types of urban air. It emphasizes the substantial contribution of local pollution sources to atmospheric PAHs and emphasizes the necessity of prioritizing control measures.

Gas–particle partitioning and dry deposition of atmospheric parent, alkylated, nitrated and hydroxyl polycyclic aromatic hydrocarbons over the Bohai sea and northern Yellow sea in autumn

To elucidate the gas–particle partitioning characteristics and dry deposition contributions of polycyclic aromatic hydrocarbons (PAHs) in the marine environment, 23 integrated air samples were collected during a research cruise in the northern Yellow Sea (NYS) and Bohai Sea (BS) in mid-autumn 2020. The atmospheric concentrations of 23 parent PAHs (PPAHs), 18 alkylated PAHs (APAHs), five nitrated PAHs (NPAHs), and seven hydroxyl PAHs (OPAHs) in gaseous and particulate phases were measured simultaneously. The total concentrations of 53 PAHs varied from 8.77 to 348 ng/m3. The 2-ring and 3-ring PPAHs and APAHs had lower particle-bound fractions than those of the NPAHs and OPAHs. For the gas–particle partitioning of the PAHs, the gas–particle partitioning coefficients (Kp) estimated using an octanol–air partition coefficient (KOA)–based model and KOA/soot–air partition coefficient (KSA) dual model (KOA–KSA dual model) were lower than the Kp measured in the field. Underestimation of the Kp commonly occurred with these models, but the KOA–KSA dual model was more suitable than the KOA–based model for gas–particle partitioning of the 53 atmospheric PAHs in the BS and NYS. The estimated atmospheric dry deposition fluxes of the 53 PAHs ranged from 631 to 14,345 ng/m2/day. The BS receives a PAHs load of up to 117 tons/year. The study provides background information on the occurrence and environmental fate of PAHs and could be vitally important for environmental safety management for the Northwest Pacific Ocean.

Comparison of Gas–Particle Partitioning of Glyoxal and Methylglyoxal in the Summertime Atmosphere at the Foot and Top of Mount Hua

Glyoxal and methylglyoxal are important volatile organic compounds in the atmosphere. The gas–particle partitioning of these carbonyl compounds makes significant contributions to O3 formation. In this study, both the gas- and particle-phase glyoxal and methylglyoxal concentrations at the foot and top of Mount Hua were determined simultaneously. The results showed that the gaseous-phase glyoxal and methylglyoxal concentrations at the top were higher than those at the foot of the mountain. However, the concentrations for the particle phase showed the opposite trend. The average theoretical values of the gas–particle partitioning coefficients of the glyoxal and methylglyoxal concentrations (4.57 × 10−10 and 9.63 × 10−10 m3 μg−1, respectively) were lower than the observed values (3.79 × 10−3 and 6.79 × 10−3 m3 μg−1, respectively). The effective Henry’s law constants (eff.KH) of the glyoxal and methylglyoxal were in the order of 108 to 109 mol/kgH2O/atm, and they were lower at the foot than they were at the top. The particle/gas ratios (P/G ratios) of the glyoxal and methylglyoxal were 0.039 and 0.055, respectively, indicating more glyoxal and methylglyoxal existed in the gas phase. The factors influencing the partitioning coefficients of the glyoxal and methylglyoxal were positively correlated with the relative humidity (RH) and negatively correlated with the PM2.5 value. Moreover, the partitioning coefficient of the glyoxal and methylglyoxal was more significant at the top than at the foot of Mount Hua.

The Atmospheric Pollution Characteristics and Health Risk Assessment of Perfluorohexane Sulfonic Acid in Beijing

Perfluorohexane sulfonic acid (PFHxS), one of the substitutes for perfluorooctane sulfonic acid (PFOS), has been widely discussed around the world. In this study, the atmospheric concentrations of PFHxS in Beijing in the summer and autumn of 2021 were monitored, and the gas–particle partitioning and wet and dry deposition characteristics were analyzed. The results show that the average total concentrations of PFHxS in Beijing in the summer and autumn were 1.61 pg/m3 and 1.41 pg/m3, respectively. The particulate fraction φ of PFHxS was about 48% during the research period, and there was a significant positive correlation between φ and air temperatures. The linear fitting relationship between logKp(gas–particle partition coefficient) and logPL (compound vapor pressure) showed that the absorption between the PFHxS molecule and particulate matter dominated the process of gas–particle partitioning. The total deposition flux of PFHxS was the largest in July and the smallest in October, with values of 55.2 and 23.7 ng/m2, respectively. During the study period, PFHxS in the atmosphere had no obvious health impacts on humans. However, with their extensive use, the possible harmful effects on children should be continuously investigated.

Gas-particle partitioning and air-water exchange of polycyclic aromatic hydrocarbons in the Three Gorges Reservoir, southwest China

A 30 m vertical drawdown water level fluctuation zone (WLFZ) was formed annually due to seasonal water impoundment in the Three Gorges Reservoir (TGR) in Southwest China. In this study, a super site in downstream of WLFZ, ∼200 km off the Three Gorges Dam, was used to investigate the seasonally gas-particle partitioning and air-water exchange of USEPA 16 polycyclic aromatic hydrocarbons (16 PAHs). The average concentrations of 16 PAHs in the particle phase were 66.63 ± 9.15 ng/m3 in winter and 8.43 ± 2.95 ng/m3 in summer. In the gas phase, they were 28.47 ± 4.79 ng/m3 in winter and 10.57 ± 1.51 ng/m3 in summer. In the dissolved phase of surface water, they were 38.65 ± 6.37 ng/L in winter and 56.53 ± 8.86 ng/L in summer. The logarithmic gas-particle partitioning coefficient (lgKp) was negatively correlated with the logarithmic subcooled liquid vapor pressure (lgPL0). While the lgKp was positively correlated with logarithmic octanol-air distribution coefficient (lgKOA). These two regressions both indicated un-equilibrium of gas-particle partitioning of PAHs in the atmosphere. Applying “Whitman two-film resistance model” to our datasets shows that 3-ring PAHs had a net volatilization from water to air (2.74–6.43 ng/m2/d), and 4 ∼ 5-ring PAHs favored deposition from air to water (−0.614 to −0.413 ng/m2/d). The water as a potential ‘source’ for 3-ring and a ‘sink’ for 4 ∼ 5-ring PAHs was thereby revealed. The results of this study are crucial for understanding atmospheric gas-particle partitioning of PAHs and for revealing the factors and mechanisms governing their geochemical cycling at air and water interfaces.

Size-resolved gas-particle partitioning characteristics of typical semi-volatile organic compounds in urban atmosphere

Understanding particle size distribution and size-resolved gas-particle partitioning of semi-volatile organic compounds (SVOCs) is important for characterizing their fate in atmosphere. However, the size-resolved gas-particle partitioning characteristics of SVOCs has not been adequately considered. To address this issue, the present study collected gaseous and size-fractioned particulate samples both in and outside of schools, offices, and residences in three districts of different urbanization levels in a megacity, Guangzhou, South China during two seasons. Typical SVOCs, including 15 polycyclic aromatic hydrocarbons (PAHs), six organophosphate esters and seven phthalic acid esters were measured. Emission sources, physicochemical properties, and environmental conditions at the sampling sites considerably impacted the spatiotemporal distribution patterns and particle size distribution of target SVOCs. Not all observed gas-particle partition coefficients (Kp) of target SVOCs were negatively correlated with subcooled liquid-vapor pressures (PL0), probably because certain factors, such as the non-exchangeable part of the particle-bound SVOCs, were not considered in traditional gas-particle partition theories. Particle size was an important factor affecting gas-particle partitioning. Adsorption was the dominant mechanism for PAHs with high molecular weight in different particle modes. A new model was established to predict size-resolved Kp of PAHs with high molecular weight based on PL0 and particle size.

Gas-PM2.5 partitioning, health risks, and sources of atmospheric PAHs in a northern China city: Impact of domestic heating

The diurnal variation, gas-particle partitioning, health risks, and sources of polycyclic aromatic hydrocarbons (PAHs) were investigated in a northern basin city of China in winter, 2020. The mean concentrations of particulate and gaseous PAHs were 87.90 ng m−3 and 69.65 ng m−3, respectively, and their concentrations were considerably enhanced during the domestic heating period. The relationship between the gas-particle partitioning coefficient of PAHs (KP) and subcooled liquid vapor pressure of PAHs (PL0) indicated organic absorption as the mechanism for this partitioning. However, the dual sorption model confirmed adsorption onto elemental carbon (EC). The health risks indicated by several equivalent parameters showed an important health effect of PAHs, especially of particulate PAHs bound onto PM2.5 during the heating period. Environmentally persistent free radicals (EPFRs) were also studied as an auxiliary parameter to evaluate the health impact of PAHs. According to the diagnostic ratios of PAHs and PMF model results, petroleum volatilization and coal combustion were the dominant sources of particulate PAHs during the non-heating and heating periods, respectively. The source apportionment results can help efficiently control PAHs and their health risks.

Formation pathway of secondary inorganic aerosol and its influencing factors in Northern China: Comparison between urban and rural sites

Secondary inorganic aerosol, including sulfate, nitrate, and ammonium (SNA), is a significant source of PM2.5 during haze episodes in Northern China. A series of high-time-resolution instruments were used in collecting PM2.5 chemical components and gaseous pollutants during a regional heavy pollution process from January 12–25, 2018, at urban and rural sites. SNA, accounting for >50% of PM2.5 at both sites, had greater importance on haze formation. Gas-phase and N2O5 hydrolysis reactions were the main formation pathways of nitrate during the daytime and nighttime, respectively. The OH radical was the primary factor for gas-phase reactions. HONO photolysis played a more critical role in OH radical formation when O3 concentration decreased during the haze episode. N2O5 hydrolysis reaction was mainly affected by O3 and aerosol water content. High relative humidity, aerosol water content, and N2O5 concentrations at the urban site enhanced the hydrolysis reactions more than those at the rural site. The aqueous-phase reactions dominated the sulfate formation with the highest rate of transition metal ion catalytic and H2O2 oxidation reactions at the urban and rural sites, respectively. Elevated relative humidity and particle acidity at the urban site resulted in a higher formation rate of aqueous-phase sulfate than at the rural site. The gas-particle partition coefficient of NH3 had a negative correlation with the particle pH, and the presence of NH3 could promote the increase of SNA concentration. Thus, more attention should be paid to the differences in SNA formation between urban and rural regions when formulating air quality policies.

Recognition and Health Impacts of Organic Pollutants with Significantly Different Proportions in the Gas Phase and Size-Fractionated Particulate Phase in Ambient Air.

The distributions of organic pollutants in the gas phase and size-fractionated particle phases can largely affect human health risks posed by them. Gas-particle partitioning and particle-size distributions of some known pollutants have been investigated. However, the pollutants which are more likely to enter the human body and cause strong adverse effects may be neglected. In this study, a nontargeted screening approach combining comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry and chemometrics was developed. Eighty-eight compounds with markedly different proportions in the gas phase and PM1, as well as 50 contaminants with significant differences in PM1 and particles with diameters of 1-2.5 μm, were identified. Of these compounds, 18 were found in the air for the first time. There were obvious discrepancies between the measured and predicted gas-particle partitioning coefficients for some pollutants, suggesting unexpected environmental fates and health risks. The human daily intakes through inhalation and dermal exposure to these pollutants were estimated with the International Commission on Radiological Protection deposition model and transdermal permeability model. A risk-based prioritization was performed. The results indicated that adverse effects posed by 9H-fluoren-9-one, 2-ethylhexyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, p-cumenol, 2,4-diisocyanato-1-methyl-benzene, bis(2-ethylhexyl) phthalate, perylene, (E)-cinnamaldehyde, 4-methyl-2-nitro-phenol, benzoic acid, and bis(2-methylpropyl) ester hexanedioic acid in ambient air may be more severe than those posed by conventionally monitored pollutants. The findings would facilitate raising concerns about these pollutants before they cause further severe and widespread impacts.

Improved atmospheric mercury simulation using updated gas-particle partition and organic aerosol concentrations

The gaseous or particulate forms of divalent mercury (HgII) significantly impact the spatial distribution of atmospheric mercury concentration and deposition flux (FLX). In the new nested-grid GEOS-Chem model, we try to modify the HgII gas-particle partitioning relationship with synchronous and hourly observations at four sites in China. Observations of gaseous oxidized Hg (GOM), particulate-bound Hg (PBM), and PM2.5 were used to derive an empirical gas-particle partitioning coefficient as a function of temperature (T) and organic aerosol (OA) concentrations under different relative humidity (RH). Results showed that with increasing RH, the dominant process of HgII gas-particle partitioning changed from physical adsorption to chemical desorption. And the dominant factor of HgII gas-particle partitioning changed from T to OA concentrations. We thus improved the simulated OA concentration field by introducing intermediate-volatility and semi-volatile organic compounds (I/SVOCs) emission inventory into the model framework and refining the volatile distributions of I/SVOCs according to new filed tests in the recent literatures. Finally, normalized mean biases (NMBs) of monthly gaseous element mercury (GEM), GOM, PBM, WFLX were reduced from −33%–29%, 95%–300%, 64%–261%, 117%–122% to −13%–0%, −20%–80%, −31%–50%, −17%–23%. The improved model explains 69%–98% of the observed atmospheric Hg decrease during 2013–2020 and can serve as a useful tool to evaluate the effectiveness of the Minamata Convention on Mercury.

Release and Gas-Particle Partitioning Behavior of Liquid Crystal Monomers during the Dismantling of Waste Liquid Crystal Display Panels in E-Waste Recycling Facilities.

Liquid crystal monomers (LCMs) are a class of emerging chemical pollutants; however, their release and gas-particle partitioning remain unknown. This study performed the first comprehensive analysis of a wide range of 93 LCMs in the ambient air of liquid crystal display (LCD) dismantling facilities. A total of 53 of the 93 target LCMs were detected in the air samples. The total atmospheric concentrations (gas and particles) of LCMs (∑LCMs) ranged from 68,800 to 385,000 (median of 204,000) pg/m3. Most LCMs were predominant in the gas phase, implying that their atmospheric transport would be mainly governed by gas rather than particle diffusions. Differential distribution patterns of the LCMs were observed due to their different atmospheric partitioning behaviors. Significant linear correlations were found between the gas-particle partitioning coefficients (KP) and the predicted subcooled vapor pressures (PL) and octanol-air partitioning coefficients (Koa) (p < 0.01). Compared with two equilibrium-state models, the experimentally observed particulate fractions (ϕ) fit better with the predicted values based on the Li-Ma-Yang (L-M-Y) steady-state model, and Koa was identified as a key factor determining the atmospheric fate pathways of LCMs. Our study highlights another new class of chemicals significantly contributing to the chemical mixture in the ambient air at e-waste recycling areas.

Predicting gas–particle partitioning coefficients of atmospheric molecules with machine learning

Abstract. The formation, properties, and lifetime of secondary organic aerosols in the atmosphere are largely determined by gas–particle partitioning coefficients of the participating organic vapours. Since these coefficients are often difficult to measure and to compute, we developed a machine learning model to predict them given molecular structure as input. Our data-driven approach is based on the dataset by Wang et al. (2017), who computed the partitioning coefficients and saturation vapour pressures of 3414 atmospheric oxidation products from the Master Chemical Mechanism using the COSMOtherm programme. We trained a kernel ridge regression (KRR) machine learning model on the saturation vapour pressure (Psat) and on two equilibrium partitioning coefficients: between a water-insoluble organic matter phase and the gas phase (KWIOM/G) and between an infinitely dilute solution with pure water and the gas phase (KW/G). For the input representation of the atomic structure of each organic molecule to the machine, we tested different descriptors. We find that the many-body tensor representation (MBTR) works best for our application, but the topological fingerprint (TopFP) approach is almost as good and computationally cheaper to evaluate. Our best machine learning model (KRR with a Gaussian kernel + MBTR) predicts Psat and KWIOM/G to within 0.3 logarithmic units and KW/G to within 0.4 logarithmic units of the original COSMOtherm calculations. This is equal to or better than the typical accuracy of COSMOtherm predictions compared to experimental data (where available). We then applied our machine learning model to a dataset of 35 383 molecules that we generated based on a carbon-10 backbone functionalized with zero to six carboxyl, carbonyl, or hydroxyl groups to evaluate its performance for polyfunctional compounds with potentially low Psat. The resulting saturation vapour pressure and partitioning coefficient distributions were physico-chemically reasonable, for example, in terms of the average effects of the addition of single functional groups. The volatility predictions for the most highly oxidized compounds were in qualitative agreement with experimentally inferred volatilities of, for example, α-pinene oxidation products with as yet unknown structures but similar elemental compositions.

Polycyclic aromatic compounds (PAHs, oxygenated PAHs, nitrated PAHs, and azaarenes) in air from four climate zones of China: Occurrence, gas/particle partitioning, and health risks

Polycyclic aromatic compounds (PACs) such as polycyclic aromatic hydrocarbons (PAHs) and their derivatives [oxygenated PAHs (OPAHs), nitrated PAHs (NPAHs), and azaarenes (AZAs)] are toxic and ubiquitous air pollutants. In this study, the concentrations of these PACs were determined in air obtained in spring and autumn of 2012 from urban and rural areas of the Tibetan Plateau, temperate, subtropical, and tropical climate zones in China. Average concentrations (gaseous + particulate) of ∑29PAHs, ∑15OPAHs, ∑11NPAHs, and ∑4AZAs were 928 ± 658, 54 ± 45, 5.3 ± 4.4, 14 ± 11 ng m−3 and 995 ± 635, 67 ± 38, 8.4 ± 6.1, 24 ± 16 ng m−3 in spring and autumn, respectively. Various C fractions and latitude correlated significantly with the concentrations and ratios of PACs. The slopes of the regression of gas-particle partition coefficients (Kp) of PACs on their sub-cooled liquid vapor pressures (PL0), indicated both adsorption and absorption to total suspended particles (TSP) for PAHs, OPAHs, and NPAHs in the four studied climatic zones. This result was further supported by comparing the fractions of PACs in TSP calculated from field data with those predicted by the Junge-Pankow adsorption and KOA absorption models. The concentration ratios of most OPAHs or NPAHs to their parent PAHs and of benzo[e]pyrene/benzo[a]pyrene were higher in autumn than in spring and increased with remoteness from point sources. This suggests enhanced secondary formation of PAH derivatives due to the elevated photochemical activity in autumn and longer ageing of air and associated transformation of PACs during their long-distance transport from source regions (urban sites) to rural sites. Lifetime lung cancer risk estimated from PACs ranged from 0.8 ± 0.6 to 3.1 ± 1.0 (×10−3), exceeding the value (10−5) recommended by the WHO. Gaseous PACs contributed substantially to the estimated cancer risks and their contributions increased with decreasing latitude in China.

Per- and polyfluoroalkyl substances in surface water, gas and particle in open ocean and coastal environment

A simultaneous sampling of atmospheric and seawater samples was performed in the Taiwan Western Strait, western Arctic Ocean, and the Antarctic Ocean. Analysis of both particle and gas phase PFAS in oceanic air was conducted using cascade impactor particle fractionator, cryogenic air sampler and activated charcoal fiber sorbent for the first time with application in the Taiwan Western Strait. Mean concentration of Σ12PFAS in surface seawater and atmospheric samples were 1178 pg/L and 24 pg/m3 in the Taiwan Western Strait, 430 pg/L and 6 pg/m3 in the western Arctic Ocean, and 456 pg/L and 3 pg/m3 in the Antarctic Ocean. In oceanic air from the Taiwan Western Strait, fluorotelomer alcohol (FTOH) and the ionic PFAS [perfluoroalkyl sulfonic acid (PFSA) and perfluoroalkyl carboxylic acid (PFCA)] were found in 76% and 7% respectively. Regional comparison of air/water exchange (KAW) and gas-particle (Kp) partition coefficients of PFAS in the oceanic environment indicated potential partitioning of ionic PFAS between surface seawater and oceanic air. These findings highlight the advancement in atmospheric PFAS measurements through combined novel technologies, namely size-fractionated particle sampling with cryogenic air trapping and/or activated charcoal sorption. Correlation between Kp and carbon chain length of PFAS was observed using both hyphenated techniques.

Tracing human footprint and the fate of atmospheric polycyclic aromatic hydrocarbons over the Pearl River Estuary, China: Importance of particle size

Few studies have focus on size-segregated particulate polycyclic aromatic hydrocarbons (PAHs) in the oceanic atmosphere. To better understand the impacts of anthropogenic activities on atmospheric PAHs, a heavily human-impacted estuary, the Pearl River Estuary (PRE), was chosen as a case study. We collected gaseous and size-segregated particulate samples of ambient air at two sites in the PRE, as well as from the exhaust emissions of the cruise ship used in the sampling campaign. In addition, surface seawater samples were collected. Size distribution patterns of high molecular-weight (HMW) particulate PAHs were bimodal at one site and unimodal at the other, suggesting PAHs at the former site were derived not only from long-range atmospheric transport but also from local sources. Gas–particle partition coefficients of HMW PAHs in size-segregated particles varied with particle sizes, mostly higher in fine particles (<1.8 μm). Dry deposition flux of Σ23PAHs (defined as the sum of 23 PAHs) was contributed mainly from coarse particles (>1.8 μm), and HMW PAHs with lower dry deposition velocities could be transported farther away. With respect to air–water exchange, lower MW PAHs tended to have net volatilization, whereas higher MW PAHs were likely to have net deposition. This study sheds new lights on the origins and fate of atmospheric PAHs over the PRE, and suggests the emissions of maritime traffics should be regulated. Collected near the metropolitan regions, atmospheric PAHs over the PRE were highly affected by anthropogenic activities, especially for HMW PAHs, which could pose a long-lasting impact to the oceanic atmosphere and marine organisms.

Temperature dependence of the gas-particle partitioning of selected VOCs.

The gas-particle partitioning coefficients for volatile organic compounds (VOCs) are difficult to acquire because discriminating the small mass fraction of the VOCs in the aerosol particle relative to that in the gas phase is challenging. In this paper, we report the temperature dependence of the gas-particle partitioning coefficient (Kp) for n-butanol (n-BuOH) and trichloroethylene (TCE). Using the bench-scale system that we developed, we measured the Kp of surrogate VOCs, n-BuOH, and TCE onto inorganic (ammonium sulfate, Am Sulf) and organic (succinic acid, SA) aerosol particles at a fixed relative humidity (RH) of 35%. At this RH level and temperature range of 278.15-308.15 K, the ln Kp for TCE and n-BuOH partitioning on SA aerosol particles were -27.0 ± 0.70 to -27.9 ± 0.01 and -13.9 ± 0.03 to -17.4 ± 0.17. In contrast, the ln Kp for TCE and n-BuOH partitioning on Am Sulf aerosol particles ranged from -26.4 ± 0.70 to -27.4 ± 0.71 and -14.1 ± 0.03 to -17.1 ± 0.17, respectively. Results showed that TCE fitted well with the classic van't Hoff relationship. The enthalpy of desorption (ΔHdes) for TCE was constant over the temperature range of 278.15 K to 308.15 K, behaving similarly to 1,2-dichlorobenzene. At a similar temperature range, n-BuOH partitioning into both aerosol particles exhibited nonlinear temperature dependence. The minimum ratio of ΔHdes (Am Sulf:SA) for n-BuOH partitioning on each aerosol type was at ∼278.15 K. The magnitude of the entropy ΔSdes for all VOCs was <1 kJ mol-1.

Dependence on Humidity and Aerosol Composition of the Gas-particle Partitioning of Weakly and Moderately Polar VOCs

ABSTRACT Volatile organic compounds (VOCs) dominate the class of pollutants that accumulate in the atmosphere and indoors. Assessing the gas-particle partitioning of VOCs is important to determine their fate, transport, and adverse health impacts. This work is a companion to our earlier study on the temperature dependence of VOC partitioning. Here, we report our measurement of the gas-particle partition coefficient (Kp) for weakly polar (trichloroethylene, TCE) and moderately polar (n-butanol, n-BuOH) VOCs under varying relative humidity (RH) levels onto organic and inorganic aerosols. Kp of TCE was four to five orders of magnitude lower than those of n-BuOH. Results suggest preferential sorption of the VOCs onto inorganic aerosol particles than onto organic aerosol particles. Kp values for both TCE and n-BuOH decreased as RH levels increased; the Kp for both VOCs declined sharply at an RH > 35% onto inorganic aerosol particles, whereas the Kp declined slowly onto organic aerosol particles. Partitioning of the VOCs onto organic aerosol particles was less dependent on RH levels while partitioning onto inorganic aerosol particles was important only at low RH levels. At lower RH, partitioning proceeded by adsorbing onto the aerosol particles. In contrast, at higher RH, the extremely low mass fraction of the VOCs, absorbed onto the aerosol particle’s bulk by dissolving into the aqueous phase. For organic aerosol particles, partitioning may be dominated by adsorption at all RH levels. At increasing RH levels, both VOCs partitioning onto in/organic aerosol particles exhibited similar behavior (exponential) consistent to those observed for 1,2-dichlorobenzene, therefore, insensitive to the polarity. However, at a similar RH level, polarity affects the mass fraction of the VOCs that sorbed onto the aerosol particles.

Atmospheric phthalate pollution in plastic agricultural greenhouses in Shaanxi Province, China.

Phthalate pollution in soil and vegetables in plastic agricultural greenhouses has attracted wide concern. Investigating airborne phthalates in this environment can improve understanding of air-soil or air-vegetable phthalate migration. However, studies of phthalates in plastic agricultural greenhouse air are rare. To fill this gap, 25 gas-phase and 23 particle-phase samples were collected from 12 typical plastic greenhouses in Shaanxi. 16 types of phthalates were measured by a gas chromatography-mass spectrometry system (GC-MS) to analyse their pollution features and variations. Results showed that in the air of the plastic greenhouses, the median concentration of the sum of sixteen type phthalates (∑16 phthalates) was 5305ngm-3, with 5th-95th value of 1214-9616ngm-3. Phthalates in gas-phase samples were over 100 times higher than the levels in particle-phase samples. Air phthalate concentrations in the plastic greenhouses were higher than those in the control groups (P<0.05). Air bis (2-ethylhexyl) phthalate (DEHP) and di-n-butyl phthalate (DnBP) accounted for 66.9% and 29.3% of total ∑16 phthalate concentrations, respectively. Air phthalate concentrations in the plastic greenhouses in winter were 1.1-5.3 times higher than the levels in summer respectively (P<0.05). Gas-particle partition coefficients (KP) values of DEHP in summer (median of 1.52×10-4m3μg-1) were higher than KP values of DnBP in summer (0.60×10-4m3μg-1). Log-transformed KP values of DnBP and DEHP were linear correlated to the reciprocal of air temperatures, respectively (P<0.05).