Emission factors of environmentally persistent free radicals in PM2.5 from rural residential solid fuels combusted in a traditional stove

Generation and persistency of combustion-derived environmentally persistent free radicals from phenolic compounds over a Fe2O3/SiO2 surface

Combustion of organic solid wastes releases phenolic compounds which can act as precursors in the formation of environmentally persistent free radicals (EPFRs) in the post-flame, cooling zone of waste combustion. The study investigated the generation mechanism of EPFRs from phenolic compounds catalyzed by transition metals in air atmosphere under simulated combustion conditions. Representative combustion-derived phenolic compounds were used, and SiO2 particulates containing different mass ratio of Fe2O3 were synthesized as carriers. EPFRs formed had g-factors between 1.9998 and 2.0066, indicating phenoxyl-, cyclopentadienyl-, and semiquinone-type radicals, along with paramagnetic F-centers. The promotion effect of phenolic compounds on EPFR formation during heating decreased as catechol > hydroquinone > phenol > p-cresol. This trend is related to hydroxyl groups and activation energy. In particular, catechol chemically adsorbed on Fe2O3 at 600 K led to the formation of EPFRs with relatively high spin concentrations (up to 1.28 × 1017 spin/g). Higher Fe2O3 concentrations promoted the transformation of phenoxyl-type radicals into cyclopentadienyl-type and paramagnetic F-centers. However, as the Fe2O3 loading increased from 1.25% to 5%, the density of EPFRs decreased. The findings related to the influence of various precursors and Fe2O3 concentration on EPFR formation provide valuable insights for estimating EPFR generation and associated risk during combustion processes.

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.

Airborne environmentally persistent free radicals (EPFRs) in PM2.5 from combustion sources: Abundance, cytotoxicity and potential exposure risks

As an emerging atmospheric pollutant, airborne environmentally persistent free radicals (EPFRs) are formed during many combustion processes and pose various adverse health effects. In health-oriented air pollution control, it is vital to evaluate the health effects of atmospheric fine particulate matter (PM2.5) from different emission sources. In this study, various types of combustion-derived PM2.5 were collected on filters in a partial-flow dilution tunnel sampling system from three typical emission sources: coal combustion, biomass burning, and automobile exhaust. Substantial concentrations of EPFRs were determined in PM2.5 samples and associated with significant potential exposure risks. Results from in vitro cytotoxicity and oxidative potential assays suggest that EPFRs may cause substantial generation of reactive oxygen species (ROS) upon inhalation exposure to PM2.5 from anthropogenic combustion sources, especially from automobile exhaust. This study provides important evidence for the source- and concentration-dependent health effects of EPFRs in PM2.5 and motivates further assessments to advance public health-oriented PM2.5 emission control.

Household characteristics associated with environmentally persistent free radicals in house dust in two Australian locations

The association between air pollution and adverse health outcomes has been extensively studied, and while oxidative stress in likely to be involved, the underlying mechanism(s) remain unclear. Recent studies propose environmentally persistent free radicals (EPFRs) as the missing connection between air pollution and detrimental health impacts. However, the indoor environment is rarely considered in EPFR research. We measured EPFRs in household dust from two locations in Australia and investigated household characteristics associated with EPFRs. Random forest models were built to identify important household characteristics through variable importance plots and the associations were analysed using Spearman's rho test. We found that age of house, type of garage, house outer wall material, heating method used in home, frequency of extractor fan use when cooking, traffic related air pollution, frequency of cleaning and major house renovation were important household characteristics associated with EPFRs in Australian homes. The direction of association between household characteristics and EPFRs differ between the locations. Hence, further research is warranted to determine the generalisability of our results.

Formation of Environmentally Persistent Free Radicals from the Irradiation of Polycyclic Aromatic Hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) provide a complex matrix for environmentally persistent free radicals (EPFRs) to stabilize in particulate matter, allowing them to be transported over long distances in the atmosphere while participating in light-driven reactions and causing various cardiopulmonary diseases. In this study, four PAHs ranging from three to five rings (anthracene, phenanthrene, pyrene, and benzo[e]pyrene) were investigated for EPFR formation upon photochemical and aqueous-phase aging. Through electron paramagnetic resonance (EPR) spectroscopy, it was found that approximately 10¹⁵ to 10¹⁶ spins g^-1 of EPFRs were formed from the PAH upon aging. EPR analysis also revealed that carbon-centered and monooxygen-centered radicals were predominantly formed by irradiation. However, oxidation and fused-ring matrices have added complexity to the chemical environment of these carbon-centered radicals, as observed by their g-values. This study showed that atmospheric aging results not only in the transformation of PAH-derived EPFR but also in an increase in EPFR concentrations of up to 10¹⁷ spins g^-1. Therefore, because of their stability and photosensitivity, PAH-derived EPFRs have a major impact on the environment.

Impact of Particulate Pollution on Aquatic Invertebrates

A serious global problem, air pollution poses a risk to both human and environmental health. It contains hazardous material like heavy metals, nanoparticles, and others that can create an impact on both land and marine environments. Particulate pollutants, which can enter water systems through a variety of ways, including precipitation and industrial runoff, can have a particularly adverse influence on aquatic invertebrates. Once in the water, these particles can harm aquatic invertebrates physically, physiologically, and molecularly, resulting in developmental problems and multi-organ toxicity. Further research at the cellular and molecular levels in numerous locations of the world is necessary to completely understand the impacts of particle pollution on aquatic invertebrates. Understanding how particle pollution affects aquatic invertebrates is vital as the significance of ecotoxicological studies on particulate contaminants increases. This review gives a comprehensive overview of the current understanding of how particle pollution affects aquatic invertebrates.

Nano-chlorapatite modification enhancing cadmium(II) adsorption capacity of crop residue biochars

Cadmium (Cd) contamination in rivers or lakes has attracted worldwide concerns. Biochar pyrolyzed form crop residues (CR) could adsorb Cd(II) from aquatic environments, while the removal capacity of single CR biochar is relatively low. Nano-chlorapatite (nClAP) modification can enhance metal scavenging ability, but little is known about the behaviors and mechanisms of Cd(II) adsorption by nClAP-modified CR biochars. In this study, the influences of feedstock type, pyrolysis temperature, nClAP modification and aquatic environments on Cd(II) adsorption of biochars derived from rice (RB) and wheat (WB) husks were investigated comprehensively. Results showed that the pristine RB and WB showed low and similar Cd(II) adsorption capacities, while the rise of pyrolysis temperatures from 300 to 600 °C significantly improved the adsorption capacities. The Cd(II) adsorption of both RB and WB was regarded as monolayer chemical processes controlled by chemical precipitation, surface complexation and cation exchange mechanisms. Moreover, the nClAP modification notably enhanced Cd(II) adsorption capacities from 13.2 to 39.9 mg·g^-1 of pristine biochars to 25.2-60.7 mg·g^-1 of modified biochars attributed to the improved contribution of Cd(II)-phosphate precipitation. Among all biochars, the nClAP-modified RB and WB pyrolyzed at 500 °C had the highest Cd(II) adsorption capacities with 60.7 and 48.3 mg·g^-1, respectively. These biochars could maintain good adsorption performances under the neutral-alkaline (pH 6-8), low ionic strength, high dissolved organic matter and all oxidation-reduction potential conditions. In conclusion, this study reveals the importance of nClAP modification to optimize Cd(II) adsorption of CR biochars, which provides a promising future for its practical application in aquatic Cd(II) scavenging.

The overlooked formation of environmentally persistent free radicals on particulate matter collected from biomass burning under light irradiation

BACKGROUND

The illumination process may be an important contributor to environmentally persistent free radicals (EPFRs) in atmospheric particles, but the ability of light to generate EPFRs in combustion products remains unclear.

OBJECTIVE

This paper studies the characteristics and formation mechanism of EPFRs in combustion particles after photoexcitation.

METHOD

The secondary photochemical processes and the generation and decay capability of EPFRs in size-resolved (<10 µm) biomass combustion particles were analysed by electron paramagnetic resonance (EPR) spectroscopy.

RESULT

Our results indicated that secondary EPFRs can be generated after illumination and the produced EPFRs have a lifetime of approximately 1 day. The content of secondary EPFRs after light exposure increased by 20 %-30 % compared to that of the original EPFRs. Through the analysis of components of different polarities, it was found that non-extractable substances were the main contributors to secondary EPFRs (75 %), followed by extractable organics. This study showed that metal species and quinones are important precursors for the formation of secondary EPFRs from non-extractable and extractable PM components, respectively. We found that O₂ molecules are an important factor for the formation of secondary EPFRs from organic substances without oxygen functional groups.

CONCLUSIONS

This study presents information about the effects of light and O₂ on the generation of EPFRs, and the unstable nature of secondary EPFRs has important implications for assessing the health risks of atmospheric particles.

Real-World Emission Characteristics of Environmentally Persistent Free Radicals in PM2.5 from Residential Solid Fuel Combustion

Environmentally persistent free radicals (EPFRs) can induce reactive oxygen species, causing adverse health impacts, and residential fuel (biomass and coal) combustion is believed to be an important emission source for EPFRs; however, the residential emission characteristics of EPFRs are rarely studied in the real world. Here, we conducted a field campaign evaluating the presence and characteristics of EPFRs generated from residential biomass and coal burning in rural China. The emission factors (EFs) of EPFRs (with units of 10²⁰ spins·kg^-1) in PM_2.5 from the combustion of crop residues (3.97 ± 0.47) were significantly higher than those from firewood (2.06 ± 0.19) and coal (2.13 ± 0.33) (p < 0.05). The EPFRs from residential solid fuel combustion were carbon-centered free radicals adjacent to oxygen atoms. The fuel type was a primary factor controlling EPFR discharge, explaining 68% of the variation in EPFR EFs. The emissions from biomass burning had higher EPFRs per particle than those from coal combustion. EPFRs had stronger relationships with carbonaceous components than with other incomplete combustion products. The EPFRs from biomass burning were mostly generated during the pyrolysis of fuels, while the EPFRs generated from coal combustion were mainly associated with refractory organic compounds. This study provides valuable information for evaluating the fates of EPFRs, promoting a better understanding of the health impacts of air pollution.

Indoor sources strongly contribute to exposure of Chinese urban residents to PM2.5 and NO2

Ambient fine particulate matter (diameters <2.5 µm; PM_2.5) and nitrogen dioxide (NO₂) pollution are responsible for substantial health burdens in China, contributing to a considerable proportion of global mortality. Simultaneously, the proportion of indoor smoking and cooking-induced PM_2.5 and NO₂ pollution lacks robust exposure assessment findings. Rapid poverty alleviation and urbanization affect the proportion of indoor vs outdoor sources of PM_2.5 and NO₂ exposures in China. The current understanding of air pollution and health lacks an understanding of source-specific air pollution exposure. Thus, we developed a model to estimate human exposure to pollutants originating indoors and outdoors. We found indoor sources strongly contribute to total PM_2.5 and NO₂ exposure in urban China and are comparable to outdoor sources. Cooking contributes 28.6 μg m^-3 PM_2.5 and 10.8 μg m^-3 NO₂ on average to the air people breathe, and so did smoking contributing 14.2 μg m^-3 PM_2.5 and 0.6 μg m^-3 NO₂, respectively. The results give us a clearer understanding of exposure to PM_2.5 and NO₂ from indoor and outdoor sources. Pollutant control policies on ambient exposure levels without addressing indoor air pollution in China are insufficient given our estimated exposure levels.

Does the energy consumption revolution improve the health of elderly adults in rural areas? Evidence from China

About 2.8 billion people around the world still depend on biomass as their primary energy source. This traditional custom affects the environment and severely impacts the health and life quality of the rural residents, especially in the elderly group. Based on the published data from the China Health and Retirement Longitudinal Study (CHARLS) conducted in 2018, this paper carefully explores the impact of the energy consumption revolution on the health of rural elderly adults and its response mechanism. The results from the empirical analysis show that: (1) The positive response of rural families to the energy consumption revolution can significantly improve the elderly adults' health condition; (2) The energy consumption revolution can improve the rural elderly adults' health by enhancing the home environmental sanitation (home environmental effect) and life satisfaction (psychological effect); (3) In the process of energy consumption revolution affecting the rural elderly's health, the factor age plays a negative regulatory role, in other words, the older the elderly, the lower the marginal effect of energy consumption revolution on their health improvement. This paper uses the propensity score matching method to deal with the endogenous problem of the regression model, and uses a placebo test and the substitution estimation method to check the robustness of the empirical results. As well, this research puts forward some policy suggestions, such as increasing investment in energy infrastructure in rural areas, reducing the cost of using clean energy, combining environmental energy protection with increasing energy income, and improving medical security conditions in rural areas.

Characteristics and Potential Inhalation Exposure Risks of Environmentally Persistent Free Radicals in Atmospheric Particulate Matter and Solid Fuel Combustion Particles in High Lung Cancer Incidence Area, China

Environmentally persistent free radicals (EPFRs) were previously considered an unrecognized composition of air pollutants and might help explain the long-standing medical mystery of why non-smokers develop tobacco-related diseases such as lung cancer. However, there is no investigated on EPFRs in Xuanwei rural areas, especially in high prevalence of lung cancer areas. In this study, we selected six types of coal and three types of biomass in Xuanwei, then conducted simulated combustion, and six group of atmospheric particulate matters (APMs) to explore the content and particle size distribution pattern of EPFRs and a new health risk assessment method to evaluate the risk of EPFRs in PM for adults and children. Our results show that the contribution of EPFRs for biomass combustion, coal combustion and APMs were mainly distributed in the size range of <1.1 μm, which accounted for 76.15 ± 4.14%, 74.85 ± 10.76%, and 75.23 ± 8.18% of PM3.3. The mean g factors and ΔHp-p indicated that the EPFRs were mainly oxygen-centered radicals in PM in Xuanwei. The results suggest that the health risk of EPFRs is significantly increased when the particle size distribution of EPFRs is taken into account, and coal combustion particulate matter (174.70 ± 37.86 cigarettes for an adult, 66.39 ± 14.39 cigarettes per person per year for a child) is more hazardous to humans than biomass combustion particulate matter (69.41 ± 4.83 cigarettes for an adult, 26.37 ± 1.84 cigarettes per person per year for), followed by APMs (102.88 ± 39.99 cigarettes for an adult, 39.10 ±15.20 cigarettes per person per year for) in PM3.3. Our results provides a new perspective and evidence for revealing the reason for the high incidence of lung cancer in Xuanwei, China.