Mutagenic and Cancer Risk Estimation of Particulate Bound Polycyclic Aromatic Hydrocarbons from the Emission of Different Biomass Fuels

Promotive effects of marine-derived dimethyl sulfoxide on the photodegradation of phenanthrene in the atmosphere

Dimethyl sulfoxide (DMSO), a versatile medium, is a particular component in the marine atmosphere that possibly causes polycyclic aromatic hydrocarbons (PAHs) to degrade differently than they do in the continental atmosphere. In this study, phenanthrene (Phe) was used as a model PAH in batch photochemical experiments to investigate the chemical actions of DMSO and the underlying mechanisms. The photodegradation of Phe in aqueous solutions with DMSO volume fractions from 0 % to 100 % was initiated by ultraviolet (UV) radiation and promoted by singlet oxygen, which was consistent with pseudo-first-order kinetics. Phe photodegraded faster in a mixture of DMSO and water than in water or DMSO alone, and the rate constant showed a unimodal distribution over the DMSO fraction range, peaking at 33 % DMSO (0.0333 ± 0.0009 min-1) and 40 % DMSO (0.0199 ± 0.0005 min-1) under 254 nm and 302 nm UV radiation, respectively. This interesting phenomenon was attributed to the competition of DMSO for UV radiation and singlet oxygen and changes in dissolved oxygen and free water contents caused by the interaction between DMSO and water molecules. In addition, 9,10-phenanthrenequinone (9,10-PhQ) with high cytotoxicity was the main photodegradation product of Phe under various conditions. The photodegradation rate of Phe in the mixtures of DMSO and water was comparable to its reaction rate with OH radicals, suggesting that 9,10-PhQ can be rapidly generated in the marine atmosphere, driven by a mechanism different from that in the continental or urban atmosphere. Under the presented experimental conditions, UV intensity and DMSO fraction were the primary factors that affected the photodegradation rate of Phe and 9,10-PhQ and altered their integrated toxicity. The findings of this study support the conclusion that the marine atmosphere is an essential field in the atmospheric transport of PAHs, in which DMSO is an important component that affects their photodegradation.

Summertime oxidative potential of atmospheric PM2.5 over New Delhi: Effect of aerosol ageing

Exposure to elevated particulate matter (PM) concentrations in ambient air has become a major health concern over urban areas worldwide. Reactive oxygen species (ROS) generation due to ambient PM (termed as their oxidative potential, OP) is shown to play a major role in PM-induced health effects. In the present study, the OP of the ambient PM2.5 samples, collected during summer 2019 from New Delhi, were measured using the dithiothreitol (DTT) assay. Average volume-normalized OP (OPV) was 2.9 ± 1.1 nmol DTT min-1 m-3, and mass-normalized OP (OPm) was 61 ± 29 pmol DTT min-1 μg-1. The regression statistics of OPv vs chemical species show the maximum slope of OPV with the elemental carbon (EC, r2 = 0.72) followed by water-soluble organic carbon (WSOC, r2 = 0.72), and organic carbon (OC, r2 = 0.64). A strong positive correlation between OPm and secondary inorganic aerosols (SIA, such as NH4+ and NO3- mass fractions) was also observed, indicating that the sources emitting NO2 and NH3, precursors of NO3- and NH4+, also emit DTT-active species. Interestingly, the slope value of OPv vs OC for aged aerosols (OM/OC > 1.7, f44 > 0.12 and f43 < 0.04) was 1.7 times higher than relatively fresh organic aerosols (OA, OM/OC < 1.7, f44 < 0.12, f43 > 0.04). An increase in OPv and OPoc with f44 indicates the formation of more DTT active species with the ageing of OA. A linear increase in OPoc with increasing Nitrogen/Carbon (N/C) ratio suggests that nitrogenous OA have higher OP.

A novel biomass pyrogenic index and its application coupled with black carbon for improving polycyclic aromatic hydrocarbon source identification

To accurately subdivide the sources of polycyclic aromatic hydrocarbons (PAHs), the composition characteristics of 36 total polycyclic hydrocarbons (T-PAHs; 16 parent PAHs and 20 alkylated PAHs [A-PAHs]) in biomass-residue samples were analyzed. A novel biomass pyrogenic index (BPI) was defined based on A-PAH-fingerprinting differences between biomass-combustion and petroleum sources of PAHs and the sum of the concentrations of pyrene, fluoranthene, benzo[a]anthracene, and alkylated homologs) divided by the ∑value of EPA PAHs with 2-3 rings. BPIs of < 0.5 and > 0.5 indicated that the PAHs originated mainly from biomass combustion and petroleum, respectively. And the ∑targeted A-PAH pairs influencing the BPI/black carbon (BC) ratio was used to identify PAH sources in surface-sediment samples, using 0.5 as the threshold to distinguish between different sources across the strait. The columnar sediments were used to verify the accuracy of two source-identification methods. The results revealed that the main PAH sources changed since 2005, which is highly consistent with those obtained using positive matrix factors and a changing trend in the main types of local energy use. These results highlight the significance of A-PAHs in accurately identifying PAH sources and suggest that applying compositional differences in BC from different sources for PAH-source identification merits further study.

Characterization of paddy-residue burning derived carbonaceous aerosols using dual carbon isotopes

A large scale paddy-residue burning (PRB) happens every year in the northwest Indo-Gangetic Plain (IGP) during the post-monsoon season, and winds transport pollutants from the source region up to the northern Indian Ocean affecting air quality of the IGP and marine region. In this study, day-night pairs of fine aerosol samples (n = 69) were collected during October-November over Patiala (30.2°N, 76.3°E, 250 m amsl), a site located in the source region of PRB. Carbonaceous aerosols (CA) were characterised using chemical species and dual carbon isotopes (¹³C and ¹⁴C) to estimate bio vs non-bio contributions and understand their characteristics. Percentage of bio fraction (f_bio, estimated using ¹⁴C) in CA varied from 74 % to 87 % (avg: 80 ± 3) during days and 71 % to 96 % (avg: 85 ± 7 %) during nights. Further, the f_bio was found to be better correlated with aerosol mass spectrometer derived f60 compare to levoglucosan (LG) or nssK⁺, suggesting f60 a useful proxy for PRB. The δ¹³C varied from -27.7 ‰ to -26.0 ‰ (avg: -27.0 ± 0.4 ‰) and - 28.7 ‰ to -26.4 ‰ (avg: -27.5 ± 0.7 ‰) during day and night, respectively. Measured δ¹³C of the samples was found to be more enriched than expected by 0.3 to 2.0 ‰, indicating the presence of aged CA also in Patiala even during PRB period. From f_bio versus δ¹³C correlation, and from Miller-Trans plot, δ¹³C of PRB is found to be -28.9 ± 1.1 ‰, which also infers that Miller-Trans plot can be used to understand source isotopic signature in the absence of radiocarbon measurements in aerosols. Further, the characteristics ratios of organic carbon (OC) to elemental carbon (EC) (11.9 ± 4.1), LG to potassium (K⁺) (0.84 ± 0.15), OC/LG (19.7 ± 2.0) and K⁺/EC (0.75 ± 0.27) were calculated by considering samples with f_bio higher than 0.90, which can be used for source apportionment studies. Such studies are crucial in assessing the effects of PRB on regional air quality and climate.

[Determination of 16 particle-phase polycyclic aromatic hydrocarbons in herbal incense by ultrasonic extraction-gas chromatography-mass spectrometry and analysis of emission characteristics]

Polycyclic aromatic hydrocarbons (PAHs) have attracted global attention because they are carcinogens and mutagenic to humans. To date, more than 200 PAHs have been found. The United States Environmental Protection Agency (USEPA) has designated 16 PAH species as priority control pollutants due to their highly toxic substances. Herbal incense is frequently used in daily life. As a result, it is critical to investigate its impact on human health and environmental safety. However, research on particle-phase PAHs is very limited and inapplicable. The current research focuses mainly on bamboo incense, which has a simpler formula than herbal incense.In this study, the emission factor and emission characteristics of particle-phase PAHs from herbal incense were described. A method combining ultrasonic and gas chromatography-mass spectrometry (GC-MS) was developed for the simultaneous determination of 16 particle-phase PAHs of herbal incense. The settings for extraction solvent, ultrasonic time, and instrument analysis conditions were optimized. In the test chamber, samples were collected by burning 0.8 g of herbal incense. After combustion, PAHs adsorbing on the particles of herbal incense were collected on a quartz filter. The whole filter sample was sliced and extracted with n-hexane-dichloromethane (1∶1, v/v). A rotary evaporator was used to concentrate the extract. GC-MS was used to analyze the prepared sample. The internal standard method was used to perform quantitative analysis on the target compounds. The linearities of the 16 target PAHs were good between mass concentrations of 0.1-5.0 μg/mL, with correlation coefficients greater than 0.998. The method detection limits (MDLs) of the 16 PAHs ranged from 0.4 to 3.8 ng/g. The 0.625 μg/g and 1.25 μg/g spiked recoveries ranged from 77.4% to 99.5% and 82.0% to 101.3%, respectively. The relative standard deviations (RSDs) of the 16 PAHs were ranged from 0.7% to 7.2% (n=6). The emission factors of particle-phase PAHs from five different kinds of herbal incense ranged from 4.60 to 11.89 μg/g. The highest concentration of phenanthrene (Phe) was found in 16 particle-phase individual PAHs of herbal incense. Fluoranthene (Flu), pyrene (Pyr), chrysene (Chr) and anthracene (Ant) concentration were ranked after Phe. The sum of these five proportions was 73.00%-89.97%. The proportion of Phe in herbal incense particle-phase PAHs was significantly higher than that of other indoor combustion sources. As a result, Phe could be used to identify individual PAHs in the particle-phase of herbal incense. The particle-phase PAHs were mainly distributed on the 3-ring and 4-ring, with a sum of 83.84% to 96.31% on the 3-ring and 4-ring. The proportion of high-molecular weight PAHs in the samples ranged from 44.25% to 63.31%. The proportion of low-molecular weight PAHs in the samples ranged from 36.69% to 55.75%. The incense source could be distinguished from other indoor combustion sources by its distinctive Phe/Flu ratio. The established method has high sensitivity, simple operation, and requires fewer samples. This method is suitable for rapidly detecting PAHs in burning incense. At the same time, it provides scientific data for further studies on the distribution and health effects of particle-phase PAHs of herbal incense.

Contrasting resistance of polycyclic aromatic hydrocarbons to atmospheric oxidation influenced by burning conditions

The oxidation of polycyclic aromatic hydrocarbons (PAHs) determines their lifetime, toxicity and consequent environmental and climate impacts. The residential solid fuel burning composes of a substantial fraction of PAH emissions; however, their oxidation rate is yet to be explicitly understood, which is complicated by the contrasting emission factors under different combustion conditions and their subsequent evolution in the atmosphere. Here we used a plume evolution chamber using ambient oxidants to simulate the evolution of residential solid fuel burning emissions under real-world solar radiation, and then to investigate the oxidation process of the emitted PAHs. Contrasting oxidation rate of PAHs was found to be influenced by particles with or without presence of substantial amount of black carbon (BC). In the flaming burning phase, which contained 46% of BC mass fraction and 8% of organic aerosol (OA) internally mixed with BC, the larger PAHs (with 4-7 rings) was rapidly oxidized 12% for every hour of evolution under solar radiation; however, the larger PAHs from smoldering phase tended to maintain unmodified during the evolution, when 95% of OA was externally mixed with only minor fraction of BC (<5%). This may be ascribed to the complex morphology of BC, allowing more exposure for the internally-mixed OA to the oxidants; in contrast with those externally-mixed OA which was prone to be coated by condensed secondary substances. This raises an important consideration about the particle mixing state in influencing the oxidation of PAHs, particularly the coating on PAHs which may extend their lifetime and environmental impacts.

Characteristics and Influencing Factors of Polycyclic Aromatic Hydrocarbons Emitted from Open Burning and Stove Burning of Biomass: A Brief Review

To mitigate global warming and achieve carbon neutrality, biomass has become a widely used carbon-neutral energy source due to its low cost and easy availability. However, the incomplete combustion of biomass can produce polycyclic aromatic hydrocarbons (PAHs), which are harmful to human health. Moreover, increasing numbers of wildfires in many regions caused by global warming have greatly increased the emissions of PAHs from biomass burning. To effectively mitigate PAH pollution and health risks associated with biomass usage, the concentrations, compositions and influencing factors of PAH emissions from biomass burning are summarized in this review. High PAH emissions from open burning and stove burning are found, and two- to four-ring PAHs account for a higher proportion than five- and six-ring PAHs. Based on the mechanism of biomass burning, biomass with higher volatile matter, cellulose, lignin, potassium salts and moisture produces more PAHs. Moreover, burning biomass in stoves at a high temperature or with an insufficient oxygen supply can increase PAH emissions. Therefore, the formation and emission of PAHs can be reduced by pelletizing, briquetting or carbonizing biomass to increase its density and burning efficiency. This review contributes to a comprehensive understanding of PAH pollution from biomass burning, providing prospective insight for preventing air pollution and health hazards associated with carbon neutrality.