Temperature dependence of the rain-gas and snow-gas partition coefficients for nearly a thousand chemicals.

Compared to the particle-gas partition coefficients (KPG), the rain-gas (KRG) and snow-gas (KSG) partition coefficients are also essential in studying the environmental behavior and fate of chemicals in the atmosphere. While the temperature dependence for the KPG have been extensively studied, the study for KRG and KSG are still lacking. Adsorption coefficients between water surface-air (KIA) and snow surface-air (KJA), as well as partition coefficients between water-air (KWA) and octanol-air (KOA) are vital in calculating KRG and KSG. These four basic adsorption and partition coefficients are also temperature-dependent, given by the well-known two-parameters Antoine equation logKXY = AXY+BXY/T, where KXY is the adsorption or partition coefficients, AXY and BXY are Antoine parameters (XY stand for IA, JA, WA, and OA), and T is the temperature in Kelvin. In this study, the parameters AXY and BXY are calculated for 943 chemicals, and logKXY can be estimated at any ambient temperature for these chemicals using these Antoine parameters. The results are evaluated by comparing these data with published experimental and modeled data, and the results show reasonable accuracy. Based on these coefficients, temperature-dependence of logKRG and logKSG is studied. It is found that both logKRG and logKSG are linearly related to 1/T, and Antoine parameters for logKRG and logKSG are also estimated. Distributions of the 943 chemicals in the atmospheric phases (gas, particle, and rain/snow), are illustrated in a Chemical Space Map. The findings reveal that, at environmental temperatures and precipitation days, the dominant state for the majority of chemicals is the gaseous phase. All the AXY and BXY values for logKSG, logKRG, and basic adsorption and partition coefficients, both modeled by this study and collected from published work, are systematically organized into an accessible dataset for public utilization.

Seasonal variations and sources of atmospheric EPFRs in a megacity in severe cold region: Implications for the influence of strong coal and biomass combustion.

Environmentally persistent free radicals (EPFRs) can pose exposure risks by inducing the generation of reactive oxygen species. As a new class of pollutants, EPFRs have been frequently detected in atmospheric particulate matters. In this study, the seasonal variations and sources of EPFRs in a severe cold region in Northeastern China were comprehensively investigated, especially for the high pollution events. The geomean concentration of EPFRs in the total suspended particle was 6.58 × 1013 spins/m3 and the mean level in winter was one order of magnitude higher than summer and autumn. The correlation network analysis showed that EPFRs had significantly positive correlation with carbon component, K+ and PAHs, indicating that EPFRs were primarily emitted from combustion and pyrolysis process. The source appointment by the Positive Matrix Factorization (PMF) model indicated that the dominant sources in the heating season were coal combustion (48.4%), vehicle emission (23.1%) and biomass burning (19.4%), while the top three sources in the non-heating season were others (41.4%), coal combustion (23.7%) and vehicle emissions (21.2%). It was found that the high EPFRs in cold season can be ascribed to the extensive use of fossil fuel for heating demand; while the high EPFRs occurred in early spring were caused by the large-scale opening combustion of biomass. In summary, this study provided important basic information for better understanding the pollution characteristics of EPFRs, which suggested that the implementation of energy transformation and straw utilization was benefit for the control of EPFRs in severe cold region.

Health Risk Assessment of Organophosphate Flame Retardants in Soil Across China Based on Monte Carlo Simulation.

Health risks from exposure to contaminants are generally estimated by evaluating concentrations of the contaminants in environmental matrixes. However, accurate health risk assessment is difficult because of uncertainties regarding exposures. This study aims to utilize data on the concentrations of organophosphate flame retardants (OPFRs) in surface soil across China coupled with Monte Carlo simulations to compensate for uncertainties in exposure to evaluate the health risks associated with contamination of soil with this class of flame retardants. Results revealed that concentrations of ∑OPFRs were 0.793-406 ng/g dry weight (dw) with an average of 23.2 ng/g dw. In terms of spatial distribution, higher OPFRs concentrations were found in economically developed regions. Although the values of health risk of OPFRs in soil across China were below the threshold, the high concentrations of OPFRs in soil in some regions should attract more attentions in future. Sensitivity analysis revealed that concentrations of OPFRs in soil, skin adherence factor, and exposure duration were the most sensitive parameters in health risk assessment. In summary, the study indicated that the national scale soil measurement could provide unique information on OPFRs exposure and health risk assessment, which was useful for the management of soil in China and for better understanding of the environmental fate of OPFRs in the global perspective.

Modeling historical budget for ß-Hexachlorocyclohexane (HCH) in the Arctic Ocean: A contrast to α-HCH.

The historical annual loading to, removal from, and cumulative burden in the Arctic Ocean for ß-hexachlorocyclohexane (ß-HCH), an isomer comprising 5-12% of technical HCH, is investigated using a mass balance box model from 1945 to 2020. Over the 76 years, loading occurred predominantly through ocean currents and river inflow (83%) and only a small portion via atmospheric transport (16%). ß-HCH started to accumulate in the Arctic Ocean in the late 1940s, reached a peak of 810 t in 1986, and decreased to 87 t in 2020, when its concentrations in the Arctic water and air were ∼30 ng m-3 and ∼0.02 pg m-3, respectively. Even though ß-HCH and α-HCH (60-70% of technical HCH) are both the isomers of HCHs with almost identical temporal and spatial emission patterns, these two chemicals have shown different major pathways entering the Arctic. Different from α-HCH with the long-range atmospheric transport (LRAT) as its major transport pathway, ß-HCH reached the Arctic mainly through long-range oceanic transport (LROT). The much higher tendency of ß-HCH to partition into the water, mainly due to its much lower Henry's Law Constant than α-HCH, produced an exceptionally strong pathway divergence with ß-HCH favoring slow transport in water and α-HCH favoring rapid transport in air. The concentration and burden of ß-HCH in the Arctic Ocean are also predicted for the year 2050 when only 4.4-5.3 t will remain in the Arctic Ocean under the influence of climate change.

Steady-State Based Model of Airborne Particle/Gas and Settled Dust/Gas Partitioning for Semivolatile Organic Compounds in the Indoor Environment.

Indoor semivolatile organic compounds (SVOCs), present in the air, airborne particles, settled dust, and other indoor surfaces, can enter the human body through several pathways. Knowing the partitioning between gaseous and particulate phases is important in identifying specific pathway contributions and thereby accurately assessing human exposure. Numerous studies have developed equilibrium equations to predict airborne particle/gas (P/G) partitioning in air (KP) and dust/gas (D/G) partitioning in settled dust (KD). The assumption that P/G and D/G equilibria are instantaneous for airborne and settled dust phases, commonly adopted by current indoor fate models, is not likely valid for compounds with high octanol-air partition coefficients (KOA). Here, we develop steady-state based equations to predict KP and KD in the indoor environment. Results show that these equations perform well and are verified by worldwide monitoring data. It is suggested that instantaneous steady state could work for P/G and D/G partitioning of SVOCs in indoor environments, and the equilibrium is just a special case of the steady state when log KOA < 11.38 for P/G partitioning and log KOA < 10.38 for D/G partitioning. These newly developed equations and methods provide a tool for more accurate assessment for human exposure to SVOCs in the indoor environment.

Pesticides in the atmosphere and seawater in a transect study from the Western Pacific to the Southern Ocean: The importance of continental discharges and air-seawater exchange.

The global oceans are known as terminal sink or secondary source for diffusive emission of organochlorine pesticides (OCPs) and selected current used pesticides (CUPs) into the overlaying atmosphere. Many pesticides have been widely produced worldwide, subsequently applied, and released into the environment. However, information on the occurrence patterns, spatial variability, and air-seawater exchange of pesticides is limited to easily accessible regions and, hence, only few studies are reported from the remote Southern Ocean. To fill this information gap, a large-scale ship-based sampling campaign was conducted. In the samples from this campaign, we measured concentrations of 221 pesticides. Both gaseous and aqueous samples were collected along a sampling transect from the western Pacific to the Southern Ocean (19.75° N-76.16° S) from November 2018 to March 2019. Twenty-seven individual pesticides were frequently (≥ 50%) detected in gaseous and aqueous samples. Tebuconazole, diphenylamine, myclobutanil, and hexachlorobenzene (HCB) dominated the composition profile in both phases. Spatial trends analysis in atmospheric and seawater concentrations showed a substantial level reduction from the western Pacific towards the Southern Ocean. Back-trajectory analysis showed that atmospheric pesticide concentrations were strongly influenced by air masses origins. Continental and riverine inputs are important sources of pesticides in the western Pacific and Indian Oceans. Atmospheric and seawater concentrations for the target pesticide residues in the Southern Ocean are low and evenly distributed due to the large distance from potential pollution sources as well as the effective isolation by the Antarctic Convergence (AC). Air-seawater fugacity ratios and fluxes indicated that the western Pacific and Indian Oceans were secondary sources for most pesticides emitted to the atmosphere, while the Southern Ocean was still considered to be a sink.

Prediction of the gas/particle partitioning quotient of PAHs based on ambient temperature.

Gas/particle (G/P) partitioning is an important influencing factor for the environmental fate of semi-volatile organic compounds (SVOCs). The G/P partitioning of polycyclic aromatic hydrocarbons (PAHs) is an integrated complex process due to its formation and growth concurrently with particles. Based on the large dataset of gaseous and particulate samples in a wide ambient temperature range of 50 °C, the simple empirical equations based on ambient temperature were established to predict the G/P partitioning quotient (KP) of PAHs at the temperature range from 252 K to 307 K (-21 °C to 34 °C). The performance of the empirical equations was validated by comparison with the monitoring KP of PAHs worldwide. The empirical equations exhibited good performance for the prediction of KP of PAHs based on ambient temperature. Two deviations with the prediction lines of the previous G/P partitioning models from the monitoring data of KP were observed. It was found that the deviations might be attributed to some non-considered influencing factors with the previous G/P partitioning prediction models. Therefore, further research should be conducted to study the mechanism of the G/P partitioning of PAHs, and more influencing factors should be introduced into the establishment of G/P partitioning models of PAHs. In summary, the result of the present study provided a convenient method for the prediction of KP of PAHs, which should be useful for the study of environmental fate of PAHs in atmosphere.

Dissolved polycyclic aromatic hydrocarbons from the Northwestern Pacific to the Southern Ocean: Surface seawater distribution, source apportionment, and air-seawater exchange.

Polycyclic aromatic hydrocarbons (PAHs) as a group of toxic and carcinogenic compounds are large scale globally emitted anthropogenic pollutants mainly emitted into the atmosphere. However, atmospheric transport cannot fully explain the spatial variability of PAHs in the marine atmosphere and seawater. It is hypothesized that PAHs accumulated in seawater and ocean circulation can also influence PAHs observed in air above the ocean. In order to investigate PAHs in seawater as a potential secondary source to air, we collected paired air and seawater samples during a research cruise from China to the Antarctic in 2018-2019, covering the Pacific Ocean, the Indian Ocean, and the Southern Ocean. Summed concentrations of 28 analyzed PAHs in seawater were highest in the Pacific Ocean (4000 ± 1400 pg/L), followed by the Indian Ocean (2700 ± 1000 pg/L), and the Southern Ocean (2300 ± 520 pg/L). Three-ringed PAHs dominated the composition profile. We found that PAH levels in the Pacific and Indian Oceans were strong inversely correlated with salinity and distance to the coastline. This suggests that riverine inputs and continental discharges are important sources of PAHs to the marine environment. Derived air-seawater fugacity ratios suggest that net fluxes of PAHs were from seawater to the air in the Pacific and Indian Oceans at 9.0-8100 (median: 1600) ng/m2/d and 290-2000 (median: 1300) ng/m2/d, respectively. In the Southern Ocean, the net flow of PAHs was from air to seawater with a flux of -1000-450 (median: -82) ng/m2/d. Source apportionment from two different models suggested that the largest contribution to total PAHs was from petrogenic sources (44-57%), followed by coal/wood combustion (30-31%), fossil fuel combustion (15%), and engine combustion emissions (2.8-9.5%). Higher contributions from petrogenic sources were found at sites close to coastal regions. Both coal/wood combustion and petrogenic sources are responsible for the PAH concentrations detected in the Indian and Southern Oceans.

Particle/gas partitioning for semi-volatile organic compounds (SVOCs) in Level III multimedia fugacity models: Gaseous emissions.

Atmospheric transport is a global-scale process that moves semi-volatile organic compounds (SVOCs) rapidly from source regions to remote locations, where these chemicals have never been produced or used. Particle/gas (P/G) partitioning of SVOCs during atmospheric transport governs wet and dry deposition, and thereby controls the efficiency and scope of long-range atmospheric transport and fate for these sorts of compounds. Previous work has shown that the assumption of steady state between particulate and gaseous phases in the atmosphere leads to model results that more closely match observations especially for compounds that strongly favor the particulate phase. Here, the practical application of steady-state P/G partitioning in the atmosphere in multimedia fugacity models is presented in greater detail. A method is developed whereby the fugacity of a chemical in the particle-phase is set equal to that in the gaseous phase (a pseudo equilibrium) but still maintains steady state of the chemical between air and aerosols in the atmosphere. This procedure greatly simplifies the application of multimedia fugacity models. Using this approach, a condition of steady state between air and aerosols is developed and applied in a Level III six-compartment six-fugacity model, which becomes a much simpler Level III six-compartment four-fugacity model. This newly-developed model is then applied to data observed during a monitoring program.

Particle/gas partitioning for semi-volatile organic compounds (SVOCs) in level III multimedia fugacity models: Both gaseous and particulate emissions.

Multimedia fugacity models have long been used to address the fate of toxic organic chemical emissions by providing a quantitative account of the sources, transport processes, and sinks. Recently, we have examined three level-III fugacity models (E4F (equilibrium six-compartment four-fugacity), S6F (steady-state six-compartment six-fugacity) and S4F (steady-state six-compartment four-fugacity) Models), in the context of their performance set against real-world data, and their practicality of application. Here, we discuss how the balance between gaseous and aerosol phases of emissions assumed for initial conditions affects the different model outcomes. Our results show that the S6F Model predictions closely match those of the S4F Model when chemical emissions are entirely in the gas-phase. As the particulate proportion of the emission increases, the S6F Model predictions diverge from those of the S4F Model and approach those of the E4F Model. Once the particulate portion reaches 100%, the S6F and E4F Models produce identical results: an internally inconsistent system where chemicals are not in a steady state between air and aerosols, and mass balance for both air and aerosols is not achieved. Thus, in terms of practicality, internal consistency, chemical mass balance and agreement with observations, the S4F Model is clearly the best choice.

Treatment of particle/gas partitioning using level III fugacity models in a six-compartment system.

In this paper, two level III fugacity models are developed and applied using an environmental system containing six compartments, including air, aerosols, soil, water, suspended particulate matters (SPMs), and sediments, as a "unit world". The first model, assumes equilibrium between air and aerosols and between water and SPMs. These assumptions lead to a four-fugacity model. The second model removes these two assumptions leading to a six-fugacity model. The two models, compared using four PBDE congeners, BDE-28, -99, -153, and -209, with a steady flux of gaseous congeners entering the air, lead to the following conclusions. 1. When the octanol-air partition coefficient (KOA) is less than 1011.4, the two models produce similar results; when KOA > 1011.4, and especially when KOA > 1012.5, the model results diverge significantly. 2. Chemicals are in an imposed equilibrium in the four-fugacity model, but in a steady state and not necessary an equilibrium in the six-fugacity model, between air and aerosols. 3. The results from the six-fugacity model indicate an internally consistent system with chemicals in steady state in all six compartments, whereas the four-fugacity model presents an internally inconsistent system where chemicals are in equilibrium but not a steady state between air and aerosols. 4. Chemicals are mass balanced in air and aerosols predicted by the six-fugacity model but not by the four-fugacity model. If the mass balance in air and aerosols is achieved in the four-fugacity model, the condition of equilibrium between air and aerosols will be no longer valid.