Nitrated and oxygenated polycyclic aromatic hydrocarbons (NPAHs and OPAHs) are receiving attention because of their high toxicity compared with parent PAHs. However, the experimental data of their physicochemical properties has been limited. This study proposed the gas chromatographic retention time (GC-RT) technique as an effective alternative one to determine octanol-air partition coefficients (KOA) and sub-cooled liquid vapor pressures (PL) for 11 NPAHs, 10 OPAHs, and 19 parent PAHs. The slopes and intercepts of the linear regressions between temperature versus KOA and PL were provided and can be used to estimate KOA and PL for the 40 targeted compounds at any temperature. The internal energies of phase transfer (ΔUOA) and enthalpies of vaporization (ΔHL) for all targeted compounds were also calculated using the GC-RT technique. High-molecular-weight compounds may release or absorb higher heat energy to transform between different phases. NPAHs and OPAHs had a non-ideal solution behavior with activity in octanol (γₒcₜ) in the range of 19–53 and 18–1,078, respectively, which is larger than the unity threshold. A comparison among four groups of PAH derivatives showed that a functional group (nitro-, oxygen-, chloro-, and bromo-) in PAH derivatives increased γₒcₜ for corresponding parent PAHs by tens (mono-group) to hundreds of times (di-group). This study suggests that the GC-RT method is applicable for indirectly measuring the physicochemical properties of various groups of organic compounds.

Organophosphate esters (OPEs) are ubiquitous contaminants in the environment, whereas their atmospheric processes and fate are poorly understood. The present study revealed the spatial heterogeneity and seasonal variations of traditional and novel OPEs in PM₂.₅ (particulate matter with diameters < 2.5 μm) across a megacity (including residential areas and potential source sites) in South China. Potential influencing factors on the contamination levels of OPEs were addressed. The total concentrations of 11 traditional OPEs ranging from 262 to 42,194 pg/m³ (median = 1872 pg/m³) were substantially higher than those of 10 novel OPEs (33.5–3835 pg/m³, median = 318 pg/m³). Significant spatial and temporal variations in the concentrations of most OPEs were observed. The overall district-specific contamination levels in this city showed dependence on the secondary industry sector for non-predominant OPEs and on the tertiary industry for predominant OPEs. The seasonal variations of the OPE concentrations suggest difference in their sources or influence of meteorological conditions. The correlations between the individual OPEs in PM₂.₅ are determined largely by either their applications or physicochemical properties (in particular vapor pressure). The correlations between OPE concentrations and each meteorological factor (temperature, relative humidity, wind speed, and surface solar radiation) were inconsistent (positive and negative). Wind speed had the greatest effect on the OPE levels; While most OPEs bound to PM₂.₅ were not efficiently scavenged by below-cloud rainfall. The results suggest that atmospheric half-life and Henry’s Law Constant of OPEs are also determining factors for the wind speed and rainfall influence, respectively. However, mechanisms underlying the influence of meteorological conditions on atmospheric OPEs still need further research.

Polybrominated diphenyl ether (PBDE) pollution in E-waste recycling areas has garnered great concern by scientists, the government and the public. In the current study, two typical kinds of E-wastes (printed wiring boards and plastic casings of household or office appliances) were selected to investigate the emission behaviors of individual PBDEs during the pyrolysis process. Emission factors (EFs), compositional profile, particle size distribution and gas-particle partitioning of PBDEs were explored. The mean EF values of the total PBDEs were determined at 8.1 ± 4.6 μg/g and 10.4 ± 11.3 μg/g for printed wiring boards and plastic casings, respectively. Significantly positive correlations were observed between EFs and original addition contents of PBDEs. BDE209 was the most abundant in the E-waste materials, while lowly brominated and highly brominated components (excluding BDE209) were predominant in the exhaust fumes. The distribution of total PBDEs on different particle sizes was characterized by a concentration of finer particles with an aerodynamic diameter between 0.4 μm and 2.1 μm and followed by less than 0.4 μm. Similarly, the distribution of individual species was dominated by finer particles. Most of the freshly emitted PBDEs (via pyrolysis) were liable to exist in the particulate phase with respect to the gaseous phase, particularly for finer particles. In addition, a linear relationship between the partitioning coefficient (KP) and the subcooled liquid vapor pressure (PL⁰) of the different components indicated non-equilibrium gas-particle partitioning during the pyrolysis process and suggested that absorption by particulate organic carbon, rather than surface adsorption, governed gas-particle partitioning.

Polychlorinated dibenzo-p-dioxins (PCDDs) are of global concern due to their persistence, bioaccumulation and toxicity. Although the fate of PCDDs in the environment is determined by their physical-chemical properties, such as aqueous solubility, vapor pressure, octanol/water-, air/water-, and octanol/water-partition coefficients, experimental property data on the entire set of 75 PCDD congeners are limited. The quantitative structure-property relationship (QSPR) approach is applied to predict the properties of all PCDD congeners. Experimental property data available from the literature are correlated against 16 molecular descriptors of five types. Reported and newly developed QSPR models for PCDDs are presented and reviewed. The values calculated by the best QSPRs are further adjusted to satisfy fundamental thermodynamic relationships. Although the single-descriptor models with chlorine number, molar volume, solvent accessible surface area and polarizability are based on good statistical results, these models cannot distinguish among PCDDs having the same chlorine number. The QSPR model based on the hyper-Wiener index of quantum-chemical descriptor gives useful statistical results and is able to distinguish among congeners with the same chlorine number, as well as satisfying thermodynamic relationships. The resulting consistent properties of the 75 PCDD congeners can be used for environmental modeling.

Physicochemical properties of PBDE congeners are important for modeling their transport, but data are often missing. The quantitative structure–property relationship (QSPR) approach is utilized to fill this gap. Individual research groups often report piecemeal properties through experimental measurements or estimation techniques, but these data seldom satisfy fundamental thermodynamic relationships because of errors. The data then lack internal consistency and cannot be used directly in environmental modeling. This paper critically reviews published experimental data to select the best QSPR models, which are then extended to all 209 PBDE congeners. Properties include aqueous solubility, vapor pressure, Henry's law constant, octanol–water partition coefficient and octanol–air partition coefficient. Their values are next adjusted to satisfy fundamental thermodynamic equations. The resulting values then take advantage of all measurements and provide quick references for modeling and PBDE-contaminated site assessment and remediation. PCBs are also compared with respect to their properties and estimation methods.

Two mesotrophic grassland species, Ranunculus acris and Dactylis glomerata were exposed to a range of ozone treatments (16.2–89.5 ppb 24 h mean) and two watering regimes under naturally fluctuating photosynthetically active radiation (PAR), vapour pressure deficit (VPD) and temperature. Stomatal conductance was measured throughout the experiments, and the combined data set (>1000 measurements) was analysed for effects of low and high ozone on responses to environmental stimuli. We show that when D. glomerata and R. acris were grown in 72.6–89.5 ppb ozone the stomata consistently lose the ability to respond, or have reduced response, to naturally fluctuating environmental conditions in comparison to their response in low ozone. The maximum stomatal conductance (gmax) was also significantly higher in the high ozone treatment for D. glomerata. We discuss the hypotheses for the reduced sensitivity of stomatal closure to a changing environment and the associated implications for ozone flux modelling.

Transpiration rates of six urban tree species in Beijing evaluated by thermal dissipation method for one year were correlated to environmental variables in heat, water, and pollutant groups. To sort out colinearity of the explanatory variables, their individual and joint contributions to variance of tree transpiration were determined by the variation and hierarchical partitioning methods. Majority of the variance in transpiration rates was associated with joint effects of variables in heat and water groups and variance due to individual effects of explanatory group were in comparison small. Atmospheric pollutants exerted only minor effects on tree transpiration. Daily transpiration rate was most affected by air temperature, soil temperature, total radiation, vapor pressure deficit, and ozone. Relative humidity would replace soil temperature when factors influencing hourly transpiration rate was considered.

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.

Atmospheric dry deposition is a major pathway for removal of polycyclic aromatic hydrocarbons (PAHs) from the atmosphere. Despite its significance in the atmospheric environment, measurements of the dry deposition velocity (VDD) and deposition fluxes (FDD) of PAHs are relatively limited. In this study, a passive dry deposition (PAS-DD) collector was co-deployed with passive air sampler polyurethane foam (PAS-PUF) from November 2015 to November 2016 in two major cities (Kathmandu and Pokhara), Nepal, to investigate the VDD and FDD of PAHs. The VDD of PAHs ranged from 0.25 to 0.5 cm s⁻¹ and the annual average was recorded as 0.37 ± 0.08 cm s⁻¹. On the basis of measured VDD, the FDD of ∑15PAHs in Kathmandu and Pokhara were estimated as 66 and 5 kg yr⁻¹ respectively. According to the measured VDD of Kathmandu and Pokhara in this study, and the previously published VDD data of Toronto, Canada, where the same PAS-DD collector was used, a significant multi-linear correlation (r² = 0.79, p < 0.05) was found between VDD of higher molecular weight (HMW with MW ≥ 228.3 and ≥ 4 rings) PAHs and meteorological parameters (precipitation and wind speed) and vapor pressure of PAHs. To the best of our knowledge, this enabled the development of an empirical model that can exhibit the combined effects of meteorological conditions on the VDD of HMW PAHs. The model was used to estimate the VDD values for major cities in the Indo-Gangetic Plain (IGP) region and the maximum estimated proportion of HMW PAHs deposited by dry deposition reached up to 60% of total emissions. Although PAH emissions in the IGP region pose global risks, the results of this study highlight the considerable risk for local IGP residents, due to the large dry deposition proportion of HMW PAHs.