Northwestern Indo-Gangetic Plain Research Articles

Sources and processes affecting the abundances of atmospheric NHx using δ15N over northwestern Indo-Gangetic plain

Ammonia (NH3) is the major constituent among all the reactive nitrogen species present in the atmosphere, and the most essential species for secondary inorganic aerosol formation. Recent satellite-based observations have identified the Indo-Gangetic Plain (IGP) as a major hotspot of global NH3 emission; however, the major sources and atmospheric processes affecting its abundance are poorly understood. The present study aims to understand the wintertime sources of NH3 over a semi-urban site (Patiala, 30.3°N, 76.4°E, 249 m amsl) located in the IGP using species specific δ15N in PM2.5. A distinct diurnal variation in the stable isotopic signature of total nitrogen (δ15N-TN) and ammonium (δ15N–NH4+) were observed; although, average day and night time concentrations of TN and NH4+ were similar. Mixing model results using δ15N–NH3 reveal the dominance of non-agricultural emissions (NH3 slip: 47 ± 24%) over agricultural emissions (24 ± 11%), combustion sources (19 ± 14 %), and biomass burning (10 ± 8%) for atmospheric NH3. Diurnal variability in source contributions to NH3 was insignificant. Further, significantly negative correlations of δ15N–NH4+ with ambient relative humidity (RH) and daytime NO3−-N concentration were observed, and attributed to the possibility of NH4NO3 volatilization during day-time owing to lower RH and higher temperature, resulting in isotopic enrichment of the remaining NH4+ in aerosol phase. This study, a first of its type from India, highlights the importance of non-agricultural NH3 emissions over the agriculture dominated IGP region, and the role of local meteorology on the isotopic fractionation of δ15N in aerosol NH4+.

Rice residue burning trajectories in Eastern India: current realities, scenarios of change, and implications for air quality

In 2019, the Government of India launched the National Clean Air Program to address the pervasive problem of poor air quality and the adverse effect on public health. Coordinated efforts to prevent agricultural burning of crop residues in Northwestern IGP (Indo-Gangetic Plain) have been implemented, but the practice is rapidly expanding into the populous Eastern IGP states, including Bihar, with uncertain consequences for regional air quality. This research has three objectives: (1) characterize historical rice residue burning trends since 2002 over space and time in Bihar State, (2) project future burning trajectories to 2050 under ‘business as usual’ and alternative scenarios of change, and (3) simulate air quality outcomes under each scenario to describe implications for public health. Six future burning scenarios were defined as maintenance of the ‘status quo’ fire extent, area expansion of burning at ‘business as usual’ rates, and a Northwest IGP analogue, of which both current rice yields and plausible yield intensification were considered for each case. The Community Earth System Model (CESM v2.1.0) was used to characterize the mid-century air quality impacts under each scenario. These analyses suggest that contemporary Bihar State burning levels contribute a small daily average proportion (8.1%) of the fine particle pollution load (i.e. PM2.5, particles ⩽2.5 μm) during the burning months, but up to as much as 62% on the worst of winter days in Bihar’s capital region. With a projected 142% ‘business as usual’ increase in burned area extent anticipated for 2050, Bihar’s capital region may experience the equivalent of 30 PM2.5 additional exceedance days, according to the WHO standard (24 h; exceedance level: 15 µg m−3), due to rice residue burning alone in the October to December period. If historical burning trends intensify and Bihar resembles the Northwest States of Punjab and Haryana by 2050, 46 d would exceed the WHO standard for PM2.5 in Bihar’s capital region.

Aging of biomass burning emissions in the Indo-Gangetic Plain outflow: Implications for black carbon light-absorption enhancement

Recent studies worldwide have demonstrated that coating on atmospheric black carbon (BC) aerosol enhances its absorption potential. However, studies quantifying the light-absorption enhancement (Eabs) of BC are extremely limited over the Indian region. The northwestern Indo-Gangetic Plain (IGP) region witnesses annual episodes of substantial crop-residue burning during the post-monsoon season (PoMS), which has been attracting wide attention due to its impact on regional air quality and aerosol characteristics. Chemical aging of these biomass burning (BB) emissions occurs during its long-range transport across the IGP by the weak westerlies, and such atmospheric processing affects their chemical, optical, and radiative properties over downwind locations. This study examines the impact of atmospheric aging of biomass burning emissions on BC light-absorption enhancement (Eabs) using extensive, simultaneous measurements of single particle refractory BC and near-real-time mass spectrometry measurements of non-refractory submicron aerosols from an IGP outflow site. It was observed that organics were the dominant submicron aerosol species, and positive matrix factorization analysis of the organics mass spectra suggested that a large fraction of organics (64%) was secondary in nature. The BC particles in the IGP outflow (mass median diameter ∼ 0.18 ± 0.01 μm) were found to be thickly coated with volume-weighted bulk relative coating thickness in the range of 1.3–1.8. The evolution of biomass-burning organic aerosols (BBOA) indicated the presence of significant amounts of aged BBOA during the PoMS. Further, the oxidation products from the evolution of BB emissions contributed to enhanced coatings (∼ 30–70%) on BC. Mie core-shell theory calculations were then used to assess the changes in BC light absorption characteristics due to the coating of non-refractory mass on its cores. It was found that thick coatings on BC led to significant light-absorption enhancement (Eabs) (bulk Eabs in the range of 1.14–1.94 at 550 nm, depending on the extent of coating). Increased Eabs values of ≥1.8 were seen when the coating on BC exceeded 60% of its core size. The modeled bulk Eabs at 550 nm depicted a better association with highly oxidized secondary organic aerosols (SOA) than sulfate among the secondary aerosol species, suggesting an SOA-dominant regime. The present findings suggest that the critical impact of the aging of BC and co-emitted species from widespread BB emissions in the IGP outflow should be considered when evaluating the regional radiative implications.

Integrated nutrient management modules for utilization of crop residues to enhance the productivity of rice-wheat systems in the north-western Indo-Gangetic plain

Integrated nutrient management modules for utilization of crop residues to enhance the productivity of rice-wheat systems in the north-western Indo-Gangetic plain

Remarkably High Oxidative Potential of Atmospheric PM2.5 Coming from a Large-Scale Paddy-Residue Burning over the Northwestern Indo-Gangetic Plain

Remarkably High Oxidative Potential of Atmospheric PM_2.5 Coming from a Large-Scale Paddy-Residue Burning over the Northwestern Indo-Gangetic Plain

Absorption and radiative characteristics of brown carbon aerosols during crop residue burning in the source region of Indo-Gangetic Plain

The north-western Indo-Gangetic Plain (IGP) experiences massive crop-residue burning (viz. paddy and wheat) on an annual and seasonal basis. The long-range transport of the particulates emitted from paddy- and wheat-residue burning (expressed as PRB and WRB, respectively) degrades the air quality, perturb the radiative budget, and alter the atmospheric chemistry of downwind IGP locations. Therefore, chemical, absorption and radiative characteristics of carbonaceous aerosols (total carbon; TC) were explored in this study. The fraction of TC in ambient PM2.5 (particulates with aerodynamic diameter ≤ 2.5 μm) was ~45% during PRB and ~24% during WRB. However, biomass burning emissions were the predominant source of TC during both PRB and WRB. The brown carbon (BrC) aerosols at Beas were ~2–3 times more abundant during PRB than in WRB. However, the absorption properties such as mass absorption efficiency and imaginary component of the refractive index for BrC at 405 nm (expressed as MAEBrC-405, kBrC-405, respectively) and radiative characteristics such as light absorption capacity were similar during both PRB and WRB. The similarity between these absorption and radiative characteristics indicate that BrC aerosols emitted during the burning of different biomass may depend only on their combustion condition. Further, the increased biomass burning emissions were linked with enhancement in the light absorption capacity of BrC during PRB. A similar light absorption capacity was observed (~30 W/g) for water-soluble BrC (WS-BrC) and total BrC during PRB. Moreover, the % contribution of BrC and EC to their total direct radiative forcing (DRFTC) during PRB and WRB (~40% and ~60% for BrC and EC, respectively) were also similar. The WS-BrC constitutes only ~15% of DRFTC during PRB. This difference signifies that non-WS-BrC aerosols were the predominant light-absorbing species during PRB (compared to WS-BrC), which needs to be factored into global climate models to mitigate uncertainties.

Transport of aerosols and trace gases during dust and crop-residue burning events in Indo-Gangetic Plain: Influence on surface ozone levels over downwind region

Abstract The present study addresses the influence of long-range transport from dust storm (event 1) and crop-residue burning (event 2) sources over Indo-Gangetic Plain (IGP) using ground-based measurements and satellite observations. In the present study, the spatial distribution and temporal variation of ambient particulate matter (PM) were assessed at 15 air quality monitoring stations situated in Rajasthan, north-western-Indo-Gangetic Plain (NW-IGP) and downwind region. During the dust event, the daily average mass concentrations of PM2.5 and PM10 were 1.2–3.3 and 2.2–4.6 times higher than the National Ambient Air Quality Standards (NAAQS 60 μg/m3 for PM2.5 and 100 μg/m3 for PM10) across stations in the vicinity of the Thar Desert. Stations in NW-IGP showed enhancement in PM2.5 and PM10 during crop-residue burning period. Agra being a downwind site was influenced by both the events and enhancement in PM levels was observed, however ozone (O3) showed different variations during event 1 and 2. During the dust event, 6.1% reduction in the mean O3 level compared to the study period was found while a significant enhancement (15.1%) during event 2 was observed at Agra. To determine the possible reasons for different O3 trends, the variation of O3 precursors carbon monoxide (CO) and nitrogen oxides (NOx) along with the meteorological parameters was also assessed. CO and NOx levels during event 1 were reduced similar to O3 whereas during event 2 an enhancement in CO and NOx levels was observed. Satellite observations and backward air-mass trajectories suggested transport of aerosols from Thar Desert resulted in reduced O3 levels during dust event while transport of O3 precursors enhanced photochemical production of O3 during crop-residue burning period at Agra.

Change in characteristics of water-soluble and water-insoluble brown carbon aerosols during a large-scale biomass burning.

Light-absorbing organic aerosol (brown carbon (BrC)) can significantly affect Earth's radiation budget and hydrological cycle. Biomass burning (BB) is among the major sources of atmospheric BrC. In this study, day/night pair (10-h integrated) of ambient PM2.5 were sampled every day before (defined as T1, n = 21), during (T2, n = 36), and after (T3, n = 8) a large-scale paddy-residue burning during October-November over Patiala (30.2° N, 76.3° E, 250m amsl), a site located in the northwestern Indo-Gangetic Plain (IGP). PM2.5 concentration varied from ~ 90 to 500μgm-3 (average ± 1σ standard deviation 230 ± 114) with the average values of 154 ± 57, 271 ± 122, and 156 ± 18μgm-3 during T1, T2, and T3 periods, respectively, indicating the influence of BB emissions on ambient air quality. The absorption coefficient of BrC (babs) is calculated from the high-resolution absorption spectra of water-soluble and methanol-soluble organic carbon measured at 300 to 700nm, and that at 365nm (babs_365) is used as a general measure of BrC. The babs_365_Water and babs_365_Methanol ranged ~ 2 to 112Mm-1 (avg 37 ± 27) and ~ 3 to 457Mm-1 (avg 121 ± 108), respectively, suggesting a considerable presence of water-insoluble BrC. Contrasting differences were also observed in the daytime and nighttime values of babs_365_Water and babs_365_Methanol. Further, the levoglucosan showed a strong correlation with K+ (slope = 0.89 ± 0.06, R = 0.92) during the T2 period. We propose that this slope (~ 0.9) can be used as a typical characteristics of the emissions from paddy-residue burning over the IGP. Absorption Ångström exponent (AAE) showed a clear day/night variability during the T2 period, and lower AAEMethanol compared to AAEWater throughout the sampling period. Further at 365nm, average relative atmospheric radiative forcing (RRF) for BrCWater is estimated to be ~ 17%, whereas that of BrCMethanol ~ 62%with respect to elemental carbon, suggesting that BrC radiative forcing could be largely underestimated by studies those use BrCWater only as a surrogate of total BrC.

Humidity, density, and inlet aspiration efficiency correction improve accuracy of a low-cost sensor during field calibration at a suburban site in the North-Western Indo-Gangetic plain (NW-IGP)

Low-cost particulate matter (PM) sensors are now widely used by concerned citizens to monitor PM exposure despite poor validation under field conditions. Here, we report the field calibration of a ...

The impact of crop residue burning (CRB) on the diurnal and seasonal variability of the ozone and PM levels at a semi-urban site in the north-western Indo-Gangetic plain

Ozone and particulate matter (PM), $$\hbox {PM}_{10}$$ and $$\hbox {PM}_{2.5}$$ , were monitored along with meteorological parameters at a semi-urban location, Patiala, in the north-western Indo-Gangetic plain from December 2013 to November 2014. The annual mean concentration levels of $$\hbox {PM}_{10}, \hbox {PM}_{2.5}$$ and ozone were recorded as 178 $$\upmu \hbox {g} \hbox { m}^{-3}, 88~\upmu \hbox {g}\hbox { m}^{-3}$$ and 39 ppb, which also exceeded the national standards on a 24-h average basis, by 77.3% (335 days), 53.2% (338 days) and 20 days, respectively. High levels of PM ( $$\hbox {PM}_{10}$$ and $$\hbox {PM}_{2.5}$$ ) were observed in winter (58–381 and 42–270 $$\upmu \hbox {g}\hbox { m}^{-3})$$ and in the post-monsoon (71–320 and 39–320 $$\upmu \hbox {g}\hbox { m}^{-3})$$ season and a rise in the level of ozone was observed in summer (22–72 ppb) and in the post-monsoon season (23–73 ppb), respectively. The rate of ozone production was the highest during the post-harvest fire period ( $$3.94~\hbox {ppb }\hbox {O}_{3}\hbox {/h}$$ in May and 4.23 ppb $$\hbox {O}_{3}\hbox {/h}$$ in November). A Pearson correlation study showed the strong dependency of PM and ozone on meteorological variables. Relative humidity has the highest ranking for ozone and $$\hbox {PM}_{10}$$ , while wind speed has the lowest rank for ozone, $$\hbox {PM}_{10}$$ and $$\hbox {PM}_{2.5}$$ in the order of factors affecting the level of pollutants. The generalised linear model and the neural network model (for ozone) and the random forest model (for PM) outperformed on the basis of performance indices and further cross-validation was done.

Aerosol Characteristics over the Northwestern Indo-Gangetic Plain: Clear-Sky Radiative Forcing of Composite and Black Carbon Aerosol

The present study examines the aerosol characteristics over Patiala in northwestern India from October 2013 to June 2014. The average mass concentration of the total suspended particulates (TSP) varied from 117 to 301 µg m–3, with PM10 accounting for ~63–83% from October to February (P1) and decreasing to less than ~40% from March to June (P2). The aerosol optical depth (AOD500) exhibited its highest values during October (0.818) and its lowest during April (0.332), with the wavelength dependence differing significantly on a temporal scale. The Ångstrom exponent (α380-870) values indicated a relatively high quantity of fine-mode particles over the study region during P1 as compared to P2, which is consistent with the PM measurements. The average monthly mass concentration of the climate forcing agent black carbon (BC) varied from 2.4 to 12 µg m–3, with the highest mass concentration in December and the lowest in June. The average monthly single scattering albedo (SSA500) derived from the OPAC (Optical Properties of Aerosols and Clouds) model varied from 0.890 to 0.947, with lower values during P1 than P2. The average monthly clear-sky direct atmospheric aerosol radiative forcing (ATM ARF) estimated by the SBDART (Santa Barbara DISORT Atmospheric Radiative Transfer) model ranged between +12 and +36 Wm–2 over the study region. Even though the mass fraction of BC averaged over the study period was only 2.4% of the total mass of the composite aerosol, its contribution to net ATM ARF was found to be significant (> 60%), indicating that BC contributes significantly to warming on a regional scale. These results improve our understanding of the impact of BC and composite aerosol on the earth’s radiation budget and hence on regional climate.

Significance of manganese fertilization in wheat-based cropping systems of Indo-Gangetic Plain (IGP)

Manganese (Mn) is an essential micronutrient, having critical role in plant nutrition. The Mn is component of several enzymes involved in photosynthesis and other physiological processes. The intensive cultivation of rice-wheat (RW) followed since long times, along with induction of rice in non-rice growing areas, especially in north-western Indo Gangetic Plain (NW-IGP) had led to emergence of Mn deficiency, particularly in wheat crops in RW rotation. Higher leaching losses of soil Mn under submerged rice induces Mn deficiency in the subsequent wheat crops. This paper critically assesses the literature on role of Mn on crop growth, distribution of soil Mn and its dynamics, effect of different soil characteristics on soil Mn availability under different cropping systems prevalent in IGP. Soil ionic composition, moisture status, organic matter status, soil pH, cation exchange capacity are some of the soil parameters dictating Mn dynamics in soil. Higher availability of soil Mn was reported under acidic condition, which decreasedwith increase in soil pH. Literature suggests positive effects of nitrate and phosphates on soil Mn dynamics and crop yields, whereas bicarbonate and chloride application have negative effects. Plant available Mn or DTPA-Mn varied under different cropping systems showing lower availability under RW system. Fractionation studies showed that labile pools of Mn contribute very less towards total soil Mn, leaving large proportion of soil Mn non-labile in nature, thus unavailable for plant uptake. The release of Mn from soil adsorption sites varied under different cropping systems, modifying Mn supply capacity of soil. Maximum release of Mn was found under frequently irrigated sugarcanesugarcanecropping system. Such information are essentially required for developing efficient Mn fertilization scheduling to improve the yield and quality of crops in IGPs.

Variations in surface ozone and carbon monoxide in the Kathmandu Valley and surrounding broader regions during SusKat-ABC field campaign: role of local and regional sources

Abstract. Air pollution resulting from rapid urbanization and associated human activities in the Kathmandu Valley of Nepal has been leading to serious public health concerns over the past 2 decades. These concerns led to a multinational field campaign SusKat-ABC (Sustainable atmosphere for the Kathmandu Valley – Atmospheric Brown Clouds) that measured different trace gases, aerosols and meteorological parameters in the Kathmandu Valley and surrounding regions during December 2012 to June 2013 to understand local- to regional-scale processes influencing air quality of the Kathmandu Valley. This study provides information about the regional distribution of ozone and some precursor gases using simultaneous in situ measurements from a SusKat-ABC supersite at Bode, Nepal, and two Indian sites: a high-altitude site, Nainital, located in the central Himalayan region and a low-altitude site, Pantnagar, located in the Indo-Gangetic Plain (IGP). The diurnal variations at Bode showed a daytime buildup in O3 while CO shows morning and evening peaks. Similar variations (with lower levels) were also observed at Pantnagar but not at Nainital. Several events of hourly ozone levels exceeding 80 ppbv were also observed at Bode. The CO levels showed a decrease from their peak level of about 2000 ppbv in January to about 680 ppbv in June at Bode. The hourly mean ozone and CO levels showed a strong negative correlation during winter (r2 = 0.82 in January and r2 = 0.71 in February), but this negative correlation gradually becomes weaker, with the lowest value in May (r2 = 0.12). The background O3 and CO mixing ratios at Bode were estimated to be about 14 and 325 ppbv, respectively. The rate of change of ozone at Bode showed a more rapid increase ( ∼ 17 ppbv h−1) during morning than the decrease in the evening (5–6 ppbv h−1), suggesting the prevalence of a semi-urban environ. The lower CO levels during spring suggest that regional transport also contributes appreciably to springtime ozone enhancement in the Kathmandu Valley on top of the local in situ ozone production. We show that regional pollution resulting from agricultural crop residue burning in northwestern IGP led to simultaneous increases in O3 and CO levels at Bode and Nainital during the first week of May 2013. A biomass-burning-induced increase in ozone and related gases was also confirmed by a global model and balloon-borne observations over Nainital. A comparison of surface ozone variations and composition of light non-methane hydrocarbons among different sites indicated the differences in emission sources of the Kathmandu Valley and the IGP. These results highlight that it is important to consider regional sources in air quality management of the Kathmandu Valley.

Constrained simulation of aerosol species and sources during pre-monsoon season over the Indian subcontinent

This study was designed to deliver a better concurrence between model estimates and observations, of atmospheric aerosol species, and predict their spatial distribution as consistently as possible. A free running aerosol simulation (freesimu) in a general circulation model (GCM) was performed, and further the simulated aerosol optical depth (AOD) was constrained with the observed AOD. The present study was carried out during the pre-monsoon season and for the Tigerz experiment which was conducted at stations over the Indo-Gangetic plain (IGP) and the Himalayan foot-hills in northern India. Our formulation of the constrained aerosol simulation (constrsimu) was based upon an identification of the freesimu with the most consistent estimates of aerosol characteristic among the three freesimu. The three freesimu (differing in source of emissions and model horizontal resolution) were carried out with the general circulation model (GCM) of Laboratoire de Météorologie Dynamique (LMD-ZT GCM). Black carbon (BC), organic carbon (OC), and sulfate-other water soluble (Sul-ows) estimated from constrsimu amounted to 70%–100% compared to that from freesimu being 20%–50% of their measured counterparts. Among the aerosol species, the pre-monsoon mean concentration of dust was considerably high over most part of the Indian subcontinent; the anthropogenic aerosol species were, however, specifically predominant over the IGP (mostly 8–12 μg m−3 for Sul-ows, OC). The constrsimu estimated total submicron aerosol mass concentration revealed its alarmingly high value over the northern and north-western India (> 100 μg m−3 and as high as 300 μg m−3). While the high value of observed AOD was found being mainly due to dust (AOD due to dust greater than 0.3) over the northern–northwestern IGP, it was due to Sul-ows (AOD due to Sul-ows as high as 0.4) over the eastern IGP, eastern coastline, and the Bay of Bengal. Temporal trend of fine (FM) and coarse mode (CM) AOD from constrsimu estimates and that derived from Tigerz experiment were in phase with each other for most of the days and exhibited a strong positive correlation coefficient. Source of Tigerz aerosols was mainly due to a predominant influence of dust from Africa/west Asia followed by that from northwest India, and of anthropogenic emissions originating in the IGP. A 200% increase was inferred for potential black carbon emissions (using India emission inventory implemented in a GCM) to obtain a concurrence between observed and freesimu BC concentration.

Seasonality in size-segregated ionic composition of ambient particulate pollutants over the Indo-Gangetic Plain: Source apportionment using PMF

Size-segregated particulate pollutants (PM<0.95, PM0.95–1.5, PM1.5–3.0, PM3.0–7.2 and PM>7.2) were collected over Patiala (30.33°N, 76.40°E; 250 m amsl), a semi-urban city located in northwestern Indo-Gangetic Plain (IGP), during October, 2012 to September, 2013. Mass concentration of total suspended particulates (TSP), derived by summation of particulate (aerosol) mass in different size range, varied from 88 to 387 μg m−3 with highest mass concentration (∼55% of total mass) in submicron size (PM<0.95) during the entire study period, which broadly reflects relative higher contribution of various anthropogenic sources (emissions from biomass and bio-fuel burning, vehicles, thermal power plants, etc) to ambient particles. Concentration of SO42−, NO3−, NH4+, K+ and Ca2+ exhibited large variability ranging from 0.52 to 40, 0.20 to 19, 0.14 to 12, 0.06 to 5.3 and 0.08 to 5.6 μg m−3, respectively, in different size ranges with varying size distribution for most of the species, except NH4+. A strong linear correlation (r = 0.97) between (SO42− + NO3−) and (K+ + NH4+) concentrations has been observed in submicron particles collected in different seasons, suggesting the formation of secondary inorganic salts. However, relatively poor correlation is observed in higher size ranges where significant correlation between (SO42− + NO3−) and (Ca2+ + Mg2+) has been observed. These observations indicate the acid neutralization by dust in coarser modes of particles. Chemical composition of submicron particulates (PM<0.95) in different seasons as well as for whole year was used to identify PM sources through the application of Positive Matrix Factorization (PMF, version 5.0) model. Based on annual data, PMF analyses suggests that six source factors namely biomass burning emission (24%), vehicular emission (22%), secondary organic aerosols (20%), power plant emission (13%), secondary inorganic aerosols (12%) and mineral dust (9%) contribute to PM<0.95 loading over the study region. Such studies are important in dispersion modeling, health impact assessment, and planning of pollution mitigation strategies.

Size-Segregated Characteristics of Carbonaceous Aerosols over the Northwestern Indo-Gangetic Plain: Year Round Temporal Behavior

ABSTRACTSize-segregated aerosol samples (PM 7.2) were collected over Patiala (30.33°N, 76.40°E; 250 m amsl), a semi-urban city located in northwestern Indo-Gangetic Plain (IGP) during October, 2012 to September, 2013. These samples were analyzed for carbonaceous aerosols (organic carbon (OC), elemental carbon (EC) and water-soluble organic carbon (WSOC)) to study their temporal variation, prevailing emission source (s) and secondary formation processes. Annual average of total suspended particulates (TSP) concentration, estimated by adding the aerosol concentrations in different size ranges, was found to be 199 ± 82 µg m–3, varying from 88–387 µg m–3 with majority of particulate mass found in submicron size (PM 75%) and WSOC (> 80%) was observed in submicron size, suggesting that OC mainly comes from combustion and/or secondary source (s). It has been observed that almost half of OC is secondary. On the other hand, climate forcing agent EC in PM<0.95 varied from 1.1 to 9.8 µg m–3 (4.8 ± 2.2 µg m–3). High mass ratios of OC/EC (~1.5–7.2) and WSOC/OC (~0.33–0.68) indicate the relative dominance of biomass burning emission over the study region. Total carbonaceous aerosols account for ~10–59% of submicron particulates mass (PM<0.95), indicating that fine particulates are enriched with carbonaceous species. These results have implications to regional climate model development and validation.

Chemical characterization and source apportionment of aerosol at an urban area of Central Delhi, India

The concentrations of organic carbon (OC), elemental carbon (EC), water soluble inorganic ionic components (WSIC), and major & trace elements of PM10 were studied in Delhi, an urban site of the Indo Gangetic Plain (IGP), India during January 2013 to June 2014. The average mass concentration of PM10 recorded as 249.7 ± 103.9 μg m−3 (average ± standard deviation) with a range of 61.4–584.8 μg m−3. The strong seasonal variation was noticed in the mass concentration of PM10 and its chemical composition with maxima during winter (PM10: 293.9 ± 95.6 μg m−3; OC: 30.5 ± 13.7 μg m−3; EC: 15.2 ± 7.4 μg m−3) and minima during monsoon (PM10: 143.9 ± 36.3 μg m−3; OC: 19.9 ± 16.2 μg m−3; EC: 7.4 ± 5.4 μg m−3). The average concentration of major and trace elements (Na, Mg, Al, P, S, Cl, K, Ca, Si, Cr, Ti, As, Br, Pb, Fe, Zn and Mn) was accounted for ∼18.5% of PM10 mass. Results of Positive Matrix Factorization (PMF) model, HYSPLIT4 trajectory model, PSCF analysis and cluster analysis provide region of sources and its strength and types of sources of PM10 over Delhi. Positive PMF provides that the major source of PM10 are soil dust (22.7%) followed by secondary aerosols (20.5%), vehicle emissions (17.0%), fossil fuel burning (15.5%), biomass burning (12.2%), industrial emissions (7.3%) and sea salts (4.8%) at the observational site of Delhi. The cluster analysis of air mass trajectories calculated by HYSPLIT model indicates that the air mass approaches to the observational site mainly from 4 sides (north-western IGP, Pakistan (10%); north-western IGP, Northwest Asia (45%); eastern IGP (38%); Pakistan and Arabian Sea (6%)) during study. Potential Source Contribution Function (PSCF) analysis also supports the cluster analysis indicating that the concentration of PM10 mass contributed, is mainly from IGP region (Uttar Pradesh, Haryana and Punjab etc.), Afghanistan, Pakistan and surrounding areas.

Quantifying the contribution of long-range transport to particulate matter (PM) mass loadings at a suburban site in the north-western Indo-Gangetic Plain (NW-IGP)

Abstract. Many sites in the densely populated Indo-Gangetic Plain (IGP) frequently exceed the national ambient air quality standard (NAAQS) of 100 μg m−3 for 24 h average PM10 and 60 μg m−3 for 24 h average PM2.5 mass loadings, exposing residents to hazardous levels of particulate matter (PM) throughout the year. We quantify the contribution of long-range transport to elevated PM levels and the number of exceedance events through a back-trajectory climatology analysis of air masses arriving at the IISER Mohali Atmospheric Chemistry facility (30.667° N, 76.729° E; 310 m a.m.s.l.) for the period August 2011–June 2013. Air masses arriving at the receptor site were classified into six clusters, which represent synoptic-scale air-mass transport patterns. Long-range transport from the west leads to significant enhancements in the average fine- and coarse-mode PM mass loadings during all seasons. The contribution of long-range transport from the west and south-west (source regions: Arabia, Thar Desert, Middle East and Afghanistan) to coarse-mode PM varied between 9 and 57 % of the total PM10–2.5 mass. Local pollution episodes (wind speed &lt; 1 m s−1) contributed to enhanced PM2.5 mass loadings during both the winter and summer seasons and to enhanced coarse-mode PM only during the winter season. South-easterly air masses (source region: eastern IGP) were associated with significantly lower fine- and coarse-mode PM mass loadings during all seasons. The fraction of days in each season during which the PM mass loadings exceeded the national ambient air quality standard was controlled by long-range transport to a much lesser degree. For the local cluster, which represents regional air masses (source region: NW-IGP), the fraction of days during which the national ambient air quality standard (NAAQS) of 60 μg m−3 for 24 h average PM2.5 was exceeded varied between 36 % of the days associated with this synoptic-scale transport during the monsoon, and 95 % during post-monsoon and winter seasons; the fraction of days during which the NAAQS of 100 μg m−3 for the 24 h average PM10 was exceeded, varied between 48 % during the monsoon and 98 % during the post-monsoon season. Long-range transport was responsible for both, bringing air masses with a significantly lower fraction of exceedance days from the eastern IGP and air masses with a moderate increase in the fraction of exceedance days from the west (source regions: Arabia, Thar Desert, Middle East and Afghanistan). In order to bring PM mass loadings into compliance with the NAAQS and to reduce the number of exceedance days, mitigation of regional combustion sources in the NW-IGP needs to be given highest priority.

Status of Available Sulfur in Soils of North-Western Indo-Gangetic Plain and Western Himalayan region and Responses of Rice and Wheat to Applied Sulfur in Farmer’s Fields

Widespread nutrient deficiencies have emerged as the major soil-related constraints, with sulfur (S) being one among them, for sustaining rice–wheat productivity in many parts of the north-western Indo-Gangetic Plain (IGP) and the Western Himalayan region (WHR). Therefore, soils from different agricultural development blocks (ADBs) of Meerut and Jyotiba Phule Nagar (J.P. Nagar) Districts in the Upper Gangetic Plain (UGP) zone, Sonipat, and Panipat Districts in Trans-Gangetic Plain (TGP) zone, and New Tehri District in Garhwal zone of WHR were analyzed for their available S-status. Farmers’ fertilizer management practices revealed that fertilizer use was highly unbalanced, and use of S fertilizers was generally negligible. Deficiencies of S were noticed in 19–47 % of the soil samples. On-farm experiments at these sites showed that rice (Oryza sativa L.) yields improved by 0.84–1.90 t ha−1 with the additions of 30–45 kg S ha−1 on S-deficient soils of IGPs, whereas the crop response varied from 1.16 to 1.39 t ha−1 on WHR soils. Also, the residual effect of 30–45 kg S ha−1 was noticed in succeeding wheat (Trititicum aestivum L.). Averaged over S rates, 37–49 % of the applied S was recovered in the system at different locations. Skipping S application decreased the available S content of the soils (0.6–2.4 mg kg−1) compared with initial content. Substantial yield gain and economic returns due to the use of S suggested for inclusion of S in the fertilizer schedules for these soils.

Inter and Intra-Annual Variability in Aerosol Characteristics over Northwestern Indo-Gangetic Plain

This study reports the temporal characteristics of aerosols mass concentration (PM10, PM2.5, PM1), size distribution and optical depth from December 2011 to November 2013 over Patiala (30.33°N, 76.4°E, 249 a.s.l.), a site located in Indo-Gangetic Plain (IGP) in northwestern India, a region with the highest population density in the world. PM10, PM2.5, and PM1 varied from 71 to 221, 27 to 92, and 17 to 75 µg/m3, respectively, with the highest concentration of PM10 during summer of 2012, and PM2.5 and PM1 during autumn of 2013. These mass concentrations were significantly higher than National Ambient Air Quality (NAAQ) standards (PM10 = 60 and PM2.5 = 40 µg/m3), suggesting poor quality of air over IGP. Both natural and anthropogenic sources were found to be responsible for poor air quality of IGP with more contribution from the latter source as inferred from Ångström exponent (α380–870) and fine mode fraction (FMF: PM2.5/PM10) of aerosols, which have shown large temporal variability. The particle size distribution is skewed towards particles with size less than 1.00 µm and very few particles are having the size greater than 6.25 µm. Aerosol optical depth at 500 nm (AOD500) ranged from 0.36 to 0.64 and shows the highest value during summer of 2012 (0.64 ± 0.09) and autumn of 2013 (0.64 ± 0.25) and minimum (0.36 ± 0.05) in spring of 2013, further reflecting the different effects of aerosols on climate during different seasons. The relation between AOD500 and PM mass has also been investigated, which has exhibited significant seasonality and AOD500 is more sensitive towards the concentration of PM1 rather than PM2.5 and PM10. These results give insight to the relative contribution of natural as well as anthropogenic aerosol sources to their total atmospheric abundances and their possible effect on ambient air quality and Earth’s radiation balance.