Sources and characteristics of carbonaceous aerosols at Agra "World heritage site" and Delhi "capital city of India"

Water-soluble organic aerosols over South Asia - Seasonal changes and source characteristics

Water-soluble organic carbon (WSOC) has been identified as a key component in atmospheric aerosols due to its ability to act as cloud condensation nuclei (CCN) owing to their highly hygroscopic nature. This paper discusses about the spatio-temporal variability in WSOC mass concentration, sources (primary and secondary contributions), the role of long-range air-mass transport in modulating their abundance, at distinct sectors over South Asia. We found from our observations that, photochemical ageing of primary organic aerosols that are derived from biomass emissions, significantly contribute to the total WSOC budget over South Asia. The wide range of water-soluble compounds released by biomass burning can contribute directly to the WSOC fraction or undergo further atmospheric processing, such as oxidation or ageing, leading to the formation of additional WSOC. WSOC/OC (organic carbon) ratio and the correlation between the WSOC and secondary organic carbon (SOC) are used for assessing the contribution from secondary sources. The three different ratios are used to delineate different source processes; OC/EC (elemental carbon) for source identification, WSOC/OC for long-range atmospheric transport (ageing) and WSOC/SOC to understand the primary and secondary contribution of WSOC. The present investigation revealed that, the primary OC that have undergone significant chemical processing as a result of long-range transport have a substantial influence on WSOC formation over South Asia, especially in Indo Gangetic Plain outflow regions such as southern peninsular and adjacent marine regions. Overall, oxidation and ageing of primary organic aerosols emitted from biomass burning was found to serve as an important source of WSOC over South Asia.

Mass, composition, and sources of particulate matter in residential and traffic sites of an urban environment

Present study aims to assess the mass, composition, and sources of PM₁₀ and PM_2.5 (particulate matter having aerodynamic diameter less than or equal to 10 and 2.5 µm aerodynamic diameter, respectively) in Vellore city. Seasonal samples collected in traffic and residential sites were analyzed for ions, elements, organic carbon (OC), and elemental carbon (EC). Source apportionment of PM₁₀ and PM_2.5 is carried out using Chemical Mass Balance, Unmix, Positive Matrix Factorization and Principal Component Analysis receptor models. Results showed that traffic site had higher annual concentration (PM_2.5 = 62 ± 32 and PM₁₀ = 112 ± 23 µg m^-3) when compared to residential site (PM_2.5 = 54 ± 22 and PM₁₀ = 98 ± 20 µg m^-3). Al, Ca, Fe, K, and Mg known to have crustal origin dominated the element composition irrespective of PM size and sampling site. Among ions, SO₄^2- accounted highest in both sites with an average of 70 and 60% to PM_2.5 and PM₁₀ ionic mass. Elemental carbon contribution to PM mass was found highest in traffic site (PM_2.5 = 17 to 23% and PM₁₀ = 8 to 10%) than residential site (PM_2.5 = 9 to 17% and PM₁₀ = 4 to 8%). Elements, ions, OC, and EC accounted 12, 28, 34, and 16% of PM_2.5 mass and 12, 21, 20, and 8% of PM₁₀ mass, respectively. Different sources identified by the receptor models are resuspended road dust, crustal material, secondary aerosol, traffic, non-exhaust vehicular emissions, secondary nitrate, construction, cooking, and biomass burning. Since Vellore is aspiring to be a smart city, this study can help the policymakers in effectively curbing PM.

Emerging Major Role of Organic Aerosols in Explaining the Occurrence, Frequency, and Magnitude of Haze and Fog Episodes during Wintertime in the Indo Gangetic Plain

Aerosols are an important part of Earth's atmosphere. They can absorb, scatter, or reflect the incoming solar radiation, which results in heating or cooling of Earth, thus impacting its climate. It affects the health of exposed human population adversely, reduces visibility, disturbs environmental systems, and causes material damage. This study summarizes the research carried out to understand the role of aerosol load and its physicochemical characteristics on occurrence, frequency, and magnitude of haze and fog events during wintertime within the Indo Gangetic Plain (IGP) in the past decade. For most species, the highest concentration was measured during foggy events at night-time over the winter season. A few species such as water-soluble organic and inorganic carbon (WSOC and WSIC), K⁺, SO₄ ^2-, and NO₃ ^-, owing to their hygroscopic nature, were efficiently scavenged, resulting in their lower concentration within the interstitial aerosol during fog episodes. Oligomerization with hydroxy and carbonyl functional groups during AFP (activating fog period) and DFP (dissipating fog period), respectively, accompanied by acidic aerosol (having catalytic ability) and high aerosol liquid water content conditions was found to be significant. Whereas the fragmentation process was dominant along with functionalization of -RCOOH or carbonyl (aldehyde/ketone) and -RCOOH moieties during FP (fog period) and PoFP (post-fog period), respectively. Transition metals play an important role in aqueous production of secondary organic aerosol (SOA) especially during the night-time. Crustal sources had the highest scavenging efficiency along with WSOC playing an important role in nucleation scavenging. Fine droplets had a higher concentration of species with a larger fraction of highly oxidized organic matter (OM) as compared to coarse or medium size droplets. Also, a new approach to calculate absorption by black carbon (BC) and brown carbon (BrC) was proposed, which found the water-soluble brown carbon (WSBrC) absorption value in aerosol to be up to 1.8 times higher than that measured in their corresponding aqueous extracts. Organic aerosol plays a vital role in facilitating fog formation and is responsible for the longer residence time in the ambient atmosphere. Ammonia plays an important role in stabilizing organic aerosol and aids to this recurring haze-fog-haze cycle that is dominant during wintertime in the IGP. Therefore, controlling the major anthropogenic sources of organic aerosol and ammonia should be our top priority in this part of the world.

Seasonal variation, source apportionment and source attributed health risk of fine carbonaceous aerosols over National Capital Region, India

Deteriorating air quality with high levels of fine particulate matter (PM_2.5) over National Capital Region (NCR) of India is one of the serious environmental and scientific issues. In this paper, PM_2.5 samples were collected for 24 h twice or thrice a week during December 2016-December 2017 at three sites [Delhi (IG), Modinagar (MN) and Mahendragarh (HR)] over NCR to analyse the carbonaceous aerosols. Source apportionment of PM_2.5 was attempted using Principal Component analysis (PCA) and Positive Matrix Factorization (PMF) based on the analysed carbonaceous fractions [Organic carbon, Elemental carbon, Secondary organic carbon (SOC)]. Organic compounds: alkanes, hopanes, steranes, polycyclic aromatic hydrocarbons (PAHs), phthalates, levoglucosan and n-alkanoic acids were analysed to distinguish the emission sources. Total Carbonaceous Aerosols (TCA) contributed significantly (∼26%) to PM_2.5 which revealed their importance in source apportionment. Estimated SOC contributed 43.2%, 42.2% and 58.2% to OC and 5.4%, 5.3% and 7.8% to PM_2.5 at IG, MN and HR sites respectively. PCA and PMF apportion five emission sources i.e., vehicular emissions (34.6%), biomass burning (26.8%), cooking emissions (15.7%), plastic and waste burning (13.5%) and secondary organic carbon (9.5%) for PM_2.5. Source attributed health risk has also been calculated in terms of Lung cancer risk (LCR) associated with PAHs exposure and concluded that vehicular emissions (40.3%), biomass burning (38.1%), secondary organic carbon (12.8%) contributed higher to LCR (503.2 × 10^-5; ∼503 cases in 1,00,000). Health risk assessment combined with source apportionment inferences signifies the immediate implementation of emissions reduction strategies with special target on transport sector and biomass burning over the NCR of India.

Aerosol and pollutant characteristics in Delhi during a winter research campaign

Urban areas in developing countries are major sources of carbonaceous aerosols and air pollutants, pointing out the need for a detailed assessment of their levels and origin close to the source. A multi-instrument research campaign was performed in Delhi during December 2015-February 2016 aimed at exploring the pollution levels and the contribution of various sources to particulate matter (PM) concentrations, black carbon (BC) aerosols, and trace gases. The weak winds (< 5-6 m s^-1) along with the shallow boundary layer favoured the formation of thick and persistent fog conditions, which along with the high BC (24.4 ± 12.2 μg m^-3) concentrations lead to the formation of smog. Very high pollution levels were recorded during the campaign, with mean PM₁₀, PM_2.5, CO, NO, and O₃ concentrations of 245.5 ± 109.8 μg m^-3, 145.5 ± 69.5 μg m^-3, 1.7 ± 0.5 ppm, 7.9 ± 2.3 ppb, and 31.3 ± 18.4 ppb, respectively. This study focuses on examining the daily/diurnal cycles of the aerosol optical properties (extinction, scattering, absorption coefficients, single scattering albedo), as well as of PM and other pollutant concentrations, along with changes in meteorology (mixing-layer height and wind speed). In addition, the hot-spot pollution sources in the greater Delhi area were determined via bivariate plots and conditional bivariate probability function (CBPF), while the distant sources were examined via the concentration weighted trajectory (CWT) analysis. The results show that the highest aerosol absorption and scattering coefficients, PM, and trace gas concentrations are detected for weak winds (< 2 m s^-1) with a preference for eastern directions, revealing high contribution from local sources and accumulation of pollutants within urban Delhi.

Air pollution and public health: the challenges for Delhi, India

Mitigating the impact of pollution on human health worldwide is important to limit the morbidity and mortality arising from exposure to its effect. The level and type of pollutants vary in different urban and rural settings. Here, we explored the extent of air pollution and its impacts on human health in the megacity of Delhi (India) through a review of the published literature. The study aims at describing the extent of air pollution in Delhi, the magnitude of health problems due to air pollution and the risk relationship between air pollution and associated health effects. We found 234 published articles in the PubMed search. The search showed that the extent of air pollution in Delhi has been described by various researchers from about 1986 onwards. We synthesized the findings and discuss them at length with respect to reported values, their possible interpretations and any limitations of the methodology. The chemical composition of ambient air pollution is also discussed. Further, we discuss the magnitude of health problem with respect to chronic obstructive pulmonary diseases (COPD), bronchial asthma and other illnesses. The results of the literature search showed that data has been collected in last 28 years on ambient air quality in Delhi, though it lacks a scientific continuity, consistency of locations and variations in parameters chosen for reporting. As a result, it is difficult to construct a spatiotemporal picture of the air pollution status in Delhi over time. The number of sites from where data have been collected varied widely across studies and methods used for data collection is also non-uniform. Even the parameters studied are varied, as some studies focused on particulate matter ≤10 μm in aerodynamic diameter (PM10) and those ≤2.5 μm in aerodynamic diameter (PM2.5), and others on suspended particulate matter (SPM) and respirable suspended particulate matter (RSPM). Similarly, the locations of data collection have varied widely. Some of the sites were at busy traffic intersections, some on the terraces of offices and residential houses and others in university campuses or airports. As a result, the key question of the extent of pollution and its distribution across various parts of the city could be inferred. None of the studies or a combination of them could present a complete picture of the burden of diseases like COPD, bronchial asthma and other allergic conditions attributable to pollution in Delhi. Neither could it be established what fraction of the burden of the above diseases is attributable to ambient air pollution, given that other factors like tobacco smoke and indoor air pollution are also contributors to the causation of such diseases. In our discussion, we highlight the knowledge gaps and in the conclusion, we suggested what research can be undertaken to fill the these research gaps.

Wintertime carbonaceous aerosols over Dhauladhar region of North-Western Himalayas

Carbonaceous aerosols play an important role in affecting human health, radiative forcing, hydrological cycle, and climate change. As our current understanding about the carbonaceous aerosols, the source(s) and process(es) associated with them in the ecologically sensitive North-Western Himalayas are limited; this systematic study was planned to understand inherent dynamics in the mass concentration and source contribution of carbonaceous aerosols in the Dhauladhar region. During four winter months (January 2015-April 2015), 24-h PM₁₀ samples were collected every week simultaneously at the rural site of Pohara (32.19° N, 76.20° E; 750 m amsl) and the urban location of Dharamshala (32.20° N, 76.32° E; 1350 m amsl). These samples were analyzed by using thermal/optical carbon analyzer for different carbon forms. Organic carbon (OC) dominated over elemental carbon (EC) and was found to be 59.3 and 64.1% in total carbon (TC) at Pohara and Dharamshala, respectively. The respective mass concentrations of OC and EC were higher at Pohara (6.8 ± 2.3 and 4.8 ± 2.0 μg.m^-3) in comparison to that observed in Dharamshala (5.0 ± 3.1 and 2.5 ± 0.6 μg.m^-3). The OC/EC ratio at Pohara (1.51 ± 0.41) indicates the dominance of fossil fuel combustion (coal and vehicular exhaust), while at Dharamshala, an OC/EC of 2.01 ± 1.07 signified additional contribution from secondary organic carbon (SOC). Diagnostic ratios (OC/EC and char-EC/soot-EC) suggested dominance of emissions from fossil fuel combustion sources over biomass burning sources in the region. Estimated non-sea salt (nss)K⁺/OC and nssK⁺/EC ratios indicated heterogeneity within the biomass burning sources over low and high altitude locations. A strong correlation between nssK⁺ and SOC over a high altitude urban location further suggested possible conversion of gaseous precursors to carbonaceous particles during coniferous wood burning.

Chemical Constituents of Carbonaceous and Nitrogen Aerosols over Thumba Region, Trivandrum, India

Aerosol filter samples collected at a tropical coastal site Thumba over Indian region were analysed for water-soluble ions, total carbon and nitrogen, organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon/nitrogen and their sources for different seasons of the year. For the entire study period, the order of abundance of ions showed the dominance of secondary ions, such as SO₄^2-, NO₃^-, and NH₄⁺. On average, Mg²⁺ (56%), K⁺ (11%), SO₄^2- (8.8%), and Ca²⁺ (8.1%) contributions were from maritime influence. There was significant chloride depletion due to enhanced levels of inorganic acids, such as SO₄^2- and NO₃^-. Total carbon contributed 21% of the aerosol total suspended particulate matter in which 85% is organic carbon. Primary combustion-generated carbonaceous aerosols contributed 41% of aerosol mass for the entire study period. High average ratios of OC/EC (5.5 ± 1.8) and WSOC/OC (0.38 ± 0.11) suggest that organic aerosols are predominantly comprised of secondary species. In our samples, major fraction (89 ± 9%) was found to be inorganic nitrate in total nitrogen (TN). Good correlations (R ² ≥ 0.82) were observed between TN with NO₃^- plus NH₄⁺, indicating that nitrate and ammonium ions account for a significant portion of TN. The temporal variations in the specific carbonaceous aerosols and air mass trajectories demonstrated that several pollutants and/or their precursor compounds are likely transported from north western India and the oceanic regions.

Characterization of carbonaceous aerosols at Mount Lu in South China: implication for secondary organic carbon formation and long-range transport

In order to understand the sources and potential formation processes of atmospheric carbonaceous aerosols in South China, fine particle samples were collected at a high-elevation mountain site--Mount Lu (29°35' N, 115°59' E, 1165 m A.S.L.) during August-September, 2011. Eight carbonaceous fractions from particles were resolved following the IMPROVE thermal/optical reflectance protocol. During the observation campaign, the daily concentrations of PM2.5 at Mount Lu ranged from 7.69 to 116.39 μg/m(3), with an average of 58.76 μg/m(3). The observed average organic carbon (OC) and elemental carbon (EC) concentrations in PM2.5 were 3.78 and 1.28 μg/m(3), respectively. Secondary organic carbon (SOC) concentration, estimated by EC-tracer method, was 2.07 μg/m(3) on average, accounting for 45.0% of the total OC. The enhancement of secondary organic aerosol (SOA) formation was observed during cloud/fog processing, and heterogeneous acid-catalyzed reactions may have contributed to SOA formation as well. Back trajectory analysis indicated that air masses were mainly sourced from southern China during observation period, and this air mass source was featured by highest values of OC and effective carbon ratio (ECR). Relation of carbonaceous species and principal component analysis indicated that multiple sources contributed to the carbonaceous aerosols at Mount Lu.

Carbonaceous aerosols and pollutants over Delhi urban environment: Temporal evolution, source apportionment and radiative forcing

Particulate matter (PM2.5) samples were collected over Delhi, India during January to December 2012 and analysed for carbonaceous aerosols and inorganic ions (SO4(2-) and NO3(-)) in order to examine variations in atmospheric chemistry, combustion sources and influence of long-range transport. The PM2.5 samples are measured (offline) via medium volume air samplers and analysed gravimetrically for carbonaceous (organic carbon, OC; elemental carbon, EC) aerosols and inorganic ions (SO4(2-) and NO3(-)). Furthermore, continuous (online) measurements of PM2.5 (via Beta-attenuation analyser), black carbon (BC) mass concentration (via Magee scientific Aethalometer) and carbon monoxide (via CO-analyser) are carried out. PM2.5 (online) range from 18.2 to 500.6μgm(-3) (annual mean of 124.6±87.9μgm(-3)) exhibiting higher night-time (129.4μgm(-3)) than daytime (103.8μgm(-3)) concentrations. The online concentrations are 38% and 28% lower than the offline during night and day, respectively. In general, larger night-time concentrations are found for the BC, OC, NO3(-)and SO4(2-), which are seasonally dependent with larger differences during late post-monsoon and winter. The high correlation (R(2)=0.74) between OC and EC along with the OC/EC of 7.09 (day time) and 4.55 (night-time), suggest significant influence of biomass-burning emissions (burning of wood and agricultural waste) as well as secondary organic aerosol formation during daytime. Concentrated weighted trajectory (CWT) analysis reveals that the potential sources for the carbonaceous aerosols and pollutants are local emissions within the urban environment and transported smoke from agricultural burning in northwest India during post-monsoon. BC radiative forcing estimates result in very high atmospheric heating rates (~1.8-2.0Kday(-1)) due to agricultural burning effects during the 2012 post-monsoon season.

Study of the carbonaceous aerosol and morphological analysis of fine particles along with their mixing state in Delhi, India: a case study

Because of high emissions of anthropogenic as well as natural particles over the Indo-Gangetic Plains (IGP), it is important to study the characteristics of fine (PM2.5) and inhalable particles (PM10), including their morphology, physical and chemical characteristics, etc., in Delhi during winter 2013. The mean mass concentrations of fine (PM2.5) and inhalable (PM10) (continuous) was 117.6 ± 79.1 and 191.0 ± 127.6 μg m(-3), respectively, whereas the coarse mode (PM10-2.5) particle PM mass was 73.38 ± 28.5 μg m(-3). During the same period, offline gravimetric monitoring of PM2.5 was conducted for morphological analysis, and its concentration was ~37 % higher compared to the continuous measurement. Carbonaceous PM such as organic carbon (OC) and elemental carbon (EC) were analyzed on the collected filters, and their mean concentration was respectively 33.8 and 4.0 μg m(-3) during the daytime, while at night it was 41.2 and 10.1 μg m(-3), respectively. The average OC/EC ratio was 8.97 and 3.96 during the day and night, respectively, indicating the formation of secondary organic aerosols during daytime. Effective carbon ratio was studied to see the effect of aerosols on climate, and its mean value was 0.52 and 1.79 during night and day, indicating the dominance of absorbing and scattering types of aerosols respectively into the atmosphere over the study region. Elemental analysis of individual particles indicates that Si is the most abundant element (~37-90 %), followed by O (oxide) and Al. Circularity and aspect ratio was studied, which indicates that particles are not perfectly spherical and not elongated in any direction. Trajectory analysis indicated that in the months of February and March, air masses appear to be transported from the Middle Eastern part along with neighboring countries and over Thar Desert region, while in January it was from the northeast direction which resulted in high concentrations of fine particles.

Measurement of organic and elemental carbon in downtown Rome and background area: physical behavior and chemical speciation

A significant portion of the particulate matter is the total carbonaceous fraction (or total carbon, TC), composed of two main fractions, elemental carbon (EC) and organic carbon (OC), which shows a large variety of organic compounds, e.g. aliphatic, aromatic compounds, alcohols, acids, etc. In this paper, TC, EC and OC concentrations determined in a downtown Rome urban area are discussed considering the influence of meteorological conditions on the temporal-spatial aerosol distribution. Similar measurements were performed at ENEA Casaccia, an area outside Rome, which is considered as the ome background. Since 2000, TC, EC and OC measurements have been performed by means of an Ambient Carbon Particulate Monitor equipped with a NDIR detector. The EC and OC concentrations trends are compared with benzene and CO trends, which are specific indicators of autovehicular traffic, for identifying the primary EC and OC contributions and the secondary OC fraction origin. Further, a chemical investigation is reported for investigating how the main organic (i.e., n-alkanes, n-alkanoic acids, polyaromatic hydrocarbons and nitro-polyaromatic hydrocarbons) and inorganic (i.e., metals, ions) fractions vary their levels during the investigated period in relationship to new regulations and/or technological innovations.