Oxidative potential of atmospheric PM10 at five different sites of Ahmedabad, a big city in Western India

Inter-continental variability in the relationship of oxidative potential and cytotoxicity with PM2.5 mass

Most fine ambient particulate matter (PM2.5)-based epidemiological models use globalized concentration-response (CR) functions assuming that the toxicity of PM2.5 is solely mass-dependent without considering its chemical composition. Although oxidative potential (OP) has emerged as an alternate metric of PM2.5 toxicity, the association between PM2.5 mass and OP on a large spatial extent has not been investigated. In this study, we evaluate this relationship using 385 PM2.5 samples collected from 14 different sites across 4 different continents and using 5 different OP (and cytotoxicity) endpoints. Our results show that the relationship between PM2.5 mass vs. OP (and cytotoxicity) is largely non-linear due to significant differences in the intrinsic toxicity, resulting from a spatially heterogeneous chemical composition of PM2.5. These results emphasize the need to develop localized CR functions incorporating other measures of PM2.5 properties (e.g., OP) to better predict the PM2.5-attributed health burdens.

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.

Acidity and oxidative potential of atmospheric aerosols over a remote mangrove ecosystem during the advection of anthropogenic plumes

To investigate the acidity and the water-soluble oxidative potential of PM10, during the continental biomass-burning plume transport, a three-year (2018-2020) winter-time campaign was conducted over a pristine island (21.35°N, 88.32°E) of Sundarban mangrove ecosystem situated at the shore of Bay of Bengal. The average PM10 concentration over Sundarban was found to be 98.3 ± 22.2 μg m-3 for the entire study period with a high fraction of non-sea-salt- SO42- and water-soluble organic carbons (WSOC) that originated from the regional solid fuel burning. The thermodynamic E-AIM(IV) model had estimated that the winter-time aerosols over Sundarban were acidic (pH:2.4 ± 0.6) and mainly governed by non-sea-salt-SO42-. The volume and mass normalized oxidative potential of PM10 was found to be 1.81 ± 0.40 nmol DTT min-1 m-3 and 18.4 ± 6.1 pmol DTT min-1 μg-1 respectively which are surprisingly higher than several urban atmospheres across the world including IGP. The acid-digested water-soluble transition metals (Cu, Mn) show higher influences in the oxidative potential (under high aerosol acidity) compared to the WSOC. The study revealed that the advection of regional solid fuel burning plume and associated non-sea-salt-SO42- is enhancing aerosol acidity and oxidative stress that in turn alters the intrinsic properties of aerosols over such marine ecosystems rich in ecology and bio-geochemistry.

Wintertime oxidative potential of PM2.5 over a big urban city in the central Indo-Gangetic Plain

Indo-Gangetic Plain (IGP) experiences a heavy load of particulate pollution impacting the 9 % of the global population living in this region. The present study examines the dithiothreitol (DTT) assay-based oxidative potential (OP) of PM2.5 and the major sources responsible for the observed OP over the central IGP (Kanpur) during winter. The volume normalized OP (OPV) of PM2.5 varied from 2.7 to 10 nmol DTT min-1 m-3 (5.5 ± 1.5) and mass normalized OP (OPM) of PM2.5 varied from 19 to 58 pmol DTT min-1 μg-1 (34 ± 8.0), respectively. Major sources of PM2.5 were identified using the positive matrix factorization (PMF) and the contribution of these sources to observed OP was estimated through multivariate linear regression of OPv with PMF-resolved factors. Although the PM2.5 mass was dominated by secondary aerosols (SA, 28 %), followed by crustal dust (CD, 24 %), resuspended fine dust (RFD, 14 %), traffic emissions (TE, 8 %), industrial emissions (IE, 17 %), and trash burning (TB, 9 %), their proportionate contribution to OP (except SA) was different likely due to differences in redox properties of chemical species coming from these sources. The SA showed the highest contribution (23 %) to observed OP, followed by RFD (19 %), IE (8 %), TE & TB (5 %), CD (4 %), and others (36 %). Our results highlight the significance of determining the chemical composition of particulates along with their mass concentrations for a better understanding of the relationship between PM and health impacts. Such studies are still lacking in the literature, and these results have direct implications for making better mitigation strategies for healthier air quality.

Chemical and oxidative properties of fine particulate matter from near-road traffic sources

The toxicity associated with the fine particulate matter (PM2.5) has not been well studied, particularly in relation to the emissions from on-road vehicles and other sources in low- and middle-income countries such as India. Thus, a study was conducted to examine the oxidative potential (OP) of PM2.5 at a roadside (RS) site with heavy vehicular traffic and an urban background (BG) site in Mumbai using the dithiothreitol (DTT) assay. Simultaneous gravimetric PM2.5 was measured at both sites and characterized for carbonaceous constituents and water-soluble trace elements and metals. Results depicted higher PM2.5, elemental carbon (EC), and organic carbon (OC) concentrations on the RS than BG (by a factor of 1.7, 4.6, and 1.2, respectively), while BG had higher water-soluble organic carbon (WSOC) levels (by a factor of 1.4) and a higher WSOC to OC ratio (86%), likely due to the dominance of secondary aerosol formation. In contrast, the measured OPDTTv at RS (8.9 ± 5.5 nmol/min/m3) and BG (8.1 ± 6.4 nmol/min/m3) sites were similar. However, OPDTTv at BG was higher during the afternoon, suggesting the influence of photochemical transformation on measured OPDTTv at BG. At RS, OC and redox-active metals (Cu, Zn, Mn, and Fe) were significantly associated with measured OP (p < 0.05), while at BG, WSOC was most strongly associated (p < 0.05). The coefficient of divergence (COD) for PM2.5, its chemical species, and OPDTTv was >0.2, indicating spatial heterogeneity between the sites, and differences in emission sources and toxicity. The estimated hazard index (HI) was not associated with OPDTTv, indicating that current PM2.5 mass regulations may not adequately capture the health effects of PM2.5. The study highlights the need for further studies examining PM2.5 toxicity and developing toxicity-based air quality regulations.

Using benthic macroinvertebrates as bioindicators to evaluate the impact of anthropogenic stressors on water quality and sediment properties of a West African lagoon

This study aimed to investigate the impact of anthropogenic stressors (landfilling, navigation for transport of goods, cooling in fossil fuel, urbanization, industrial expansion, agriculture activities, and recreational activities) on environmental variables, microbiological quality, and sediment properties using benthic macroinvertebrates as a bioindicator within Lagos Lagoon, Nigeria. Four (4) sampling stations were established with respect to their importance/anthropogenic activities within the Lagos Lagoon. Surface water, bottom substrates, and benthic macroinvertebrate fauna samples were collected bimonthly from each sampling station for a year and analyzed using appropriate standard methods and procedures. The highest pH range of 7.96-8.01 (7.98 ± 2.35) was recorded at Site IV, while the lowest range of 6.41-7.01 (6.15 ± 1.14) was observed at Site II, and there was a significant difference (p < 0.05) among the pH mean values across the sites. High values of salinity, chloride, sodium, COD, BOD, manganese, nickel, cadmium, and nitrate were recorded among the surface water physicochemical parameters, which were above WHO (2011) permissible limits, while the high concentrations of toxic metals (Pb, Cr, Zn, and Cd) was recorded in sediment. A total of 26 species of benthic macroinvertebrates were recorded during this study, which belongs to eight (8) classes. Gastropoda recorded the highest percentage contribution of 39.12%, followed by polychaeta accounting for 30.34%, while malacostraca contributed 2.63%. The highest abundance of macroinvertebrates was recorded at Site I (256 Indiv/m2), followed by Site IV (252 Indiv/m2), and the least was observed at Site II (195 Indiv/m2). Based on the results of the physico-chemical, heavy metals, microbial quality, and macroinvertebrates assemblage obtained from this study revealed the adverse effect of anthropogenic activities on water quality degradation. It plays a significant role in the distribution and diversity of benthic macroinvertebrates in an aquatic environment.

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.

Effect of Biomass Burning, Diwali Fireworks, and Polluted Fog Events on the Oxidative Potential of Fine Ambient Particulate Matter in Delhi, India

We investigated the influence of biomass burning (BURN), Diwali fireworks, and fog events on the ambient fine particulate matter (PM_2.5) oxidative potential (OP) during the postmonsoon (PMON) and winter season in Delhi, India. The real-time hourly averaged OP (based on a dithiothreitol assay) and PM_2.5 chemical composition were measured intermittently from October 2019 to January 2020. The peak extrinsic OP (OP_v: normalized by the volume of air) was observed during the winter fog (WFOG) (5.23 ± 4.6 nmol·min^-1·m^-3), whereas the intrinsic OP (OP_m; normalized by the PM_2.5 mass) was the highest during the Diwali firework-influenced period (29.4 ± 18.48 pmol·min^-1·μg^-1). Source apportionment analysis using positive matrix factorization revealed that traffic + resuspended dust-related emissions (39%) and secondary sulfate + oxidized organic aerosols (38%) were driving the OP_v during the PMON period, whereas BURN aerosols dominated (37%) the OP_v during the WFOG period. Firework-related emissions became a significant contributor (∼32%) to the OP_v during the Diwali period (4 day period from October 26 to 29), and its contribution peaked (72%) on the night of Diwali. Discerning the influence of seasonal and episodic sources on health-relevant properties of PM_2.5, such as OP, could help better understand the causal relationships between PM_2.5 and health effects in India.

Oxidative potential associated with water-soluble components of PM2.5 in Beijing: The important role of anthropogenic organic aerosols

Oxidative stress is the mainstream toxicological mechanism for the adverse health outcomes of ambient aerosols. However, our understanding of the crucial redox-active species affecting the oxidative potential of water-soluble aerosols (OP_WS) remains limited. In this study, the OP_WS of PM_2.5 in Beijing was measured using dithiothreitol (DTT) assay, including DTT consumption rate and ·OH formation rate. OP_WS was more closely related to water-soluble organic compounds (WSOC) rather than transition metals. Laboratory simulations were conducted to investigate the effects of individual target species in the context of complex metal-organic interactions. The results showed that reducing WSOC can effectively decrease OP_WS, while reducing Cu²⁺ increased OP_WS. Parallel factor analysis demonstrated that OP_WS was the most significantly correlated with the highly oxidized humic-like or quinone-like substances. Multiple linear regression showed that aromatic secondary organic carbon (SOC) (34.4%), other primary combustion sources of WSOC (20.0%), primary biomass burning WSOC (19.8%), transition metal ions (12.9%) and biomass burning SOC (12.8%) made significant contributions to DTT_V. In addition to the anthropogenic sources of WSOC, the aged biogenic SOC also contributed to OH_V, particularly in summer. Reducing anthropogenic WSOC was the key to the effective control of OP_WS of PM_2.5 in Beijing.

Gridded distribution of total suspended particulate matter (TSP) and their chemical characterization over Delhi during winter

In the present study, total suspended particulate matter (TSP) samples were collected at 47 different sites (47 grids of 5 × 5 km² area) of Delhi during winter (January-February 2019) in campaign mode. To understand the spatial variation of sources, TSP samples were analyzed for chemical compositions including carbonaceous species [organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon (WSOC)], water-soluble total nitrogen (WSTN), water-soluble inorganic nitrogen (WSIN), polycyclic aromatic hydrocarbons (16 PAHs), water-soluble inorganic species (WSIS) (F^-, Cl^-, SO₄^2-, NO₂^-, NO₃^-, PO₄^3-, NH₄⁺, Ca²⁺, Mg²⁺, Na⁺, and K⁺), and major and minor trace elements (B, Na, Mg, Al, P, S, Cl, K, Ca, Ti, Fe, Zn, Cr, Mn, Cu, As, Pd, F, and Ag). During the campaign, the maximum concentration of several components of TSP (996 μg/m³) was recorded at the Rana Pratap Bagh area, representing a pollution hotspot of Delhi. The maximum concentrations of PAHs were recorded at Udhyog Nagar, a region close to heavily loaded diesel vehicles, small rubber factories, and waste burning areas. Higher content of Cl^- and Cl^-/Na⁺ ratio (>1.7) suggests the presence of nonmarine anthropogenic sources of Cl^- over Delhi. Minimum concentrations of OC, EC, WSOC, PAHs, and WSIS in TSP were observed at Kalkaji, representing the least polluted area in Delhi. Enrichment factor <5.0 at several locations and a significant correlation of Al with Mg, Fe, Ti, and Ca and C/N ratio indicated the abundance of mineral/crustal dust in TSP over Delhi. Principal component analysis (PCA) was also performed for the source apportionment of TSP, and extracted soil dust was found to be the major contributor to TSP, followed by biomass burning, open waste burning, secondary aerosol, and vehicular emissions.

Health impact assessment from exposure to trace metals present in atmospheric PM10 at Ahmedabad, a big city in western India

Many toxicological studies revealed the deleterious effects on human health induced by trace metals in ambient particulate matter (PM). This study reports the season-dependent water-soluble and total metal mass in PM₁₀ collected simultaneously over five microenvironments in a semi-arid urban region, Ahmedabad, located in western India. The mineral dust fraction in PM₁₀ over Bapunagar, Narol, Paldi, Income Tax, and Science City was estimated to be around 39, 45, 47, 44, and 31% during summer (May-June 2017) and 24, 55, 28, 27, and 28% during winter (December 2017-January 2018), respectively, corroborating mineral dust is perennial in the air over Ahmedabad. The PM_2.5/PM₁₀ mass ratios over all the sites were higher during winter (40-60%) as compared to those during summer (30-40%), indicating the contribution from the anthropogenic sources to PM mass. Among the metals monitored, the estimated considerable amount of high masses of Zn, Cu, Ni, Cd, and Sb during winter can be ascribed to the anthropogenic inputs based on the estimated enrichment factors (EF). In contrast to the crustal source, these metals might have been possibly emitted from several other man-made sources, which were found to be more water-soluble during both seasons. As per the standards of incremental excess lifetime cancer risk (IELCR), it is estimated that the atmospheric mass concentration of carcinogenic metals such as Cr, Co, and As was higher in all these sites, whereas the metals such as Pb, Ni, and Cd are also found over the industrial site (Narol) in addition to the above-said metals. Notably, people are highly susceptible to these metals, leading to the potential risk of cancer during both seasons.