Aerosol emissions from biomass burning are of specific interest over the globe due to their strong radiative impacts and climate implications. The present study examines the impact of paddy crop residue burning over northern India during the postmonsoon (October-November) season of 2012 on modification of aerosol properties, as well as the long-range transport of smoke plumes, altitude characteristics, and affected areas via the synergy of ground-based measurements and satellite observations. During this period, Moderate Resolution Imaging Spectroradiometer (MODIS) images show a thick smoke/hazy aerosol layer below 2-2.5 km in the atmosphere covering nearly the whole Indo-Gangetic Plains (IGP). The air mass trajectories originating from the biomass-burning source region over Punjab at 500 m reveal a potential aerosol transport pathway along the Ganges valley from west to east, resulting in a strong aerosol optical depth (AOD) gradient. Sometimes, depending upon the wind direction and meteorological conditions, the plumes also influence central India, the Arabian Sea, and the Bay of Bengal, thus contributing to Asian pollution outflow. The increased number of fire counts (Terra and Aqua MODIS data) is associated with severe aerosol-laden atmospheres (AOD 500 nm > 1.0) over six IGP locations, high values of Ångström exponent (>1.2), high particulate mass 2.5 (PM 2.5 ) concentrations (>100-150 μgm À3 ), and enhanced Ozone Monitoring Instrument Aerosol Index gradient (~2.5) and NO 2 concentrations (~6 × 10 15 mol/cm 2 ), indicating the dominance of smoke aerosols from agricultural crop residue burning. The aerosol size distribution is shifted toward the fine-mode fraction, also exhibiting an increase in the radius of fine aerosols due to coagulation processes in a highly turbid environment. The spectral variation of the single-scattering albedo reveals enhanced dominance of moderately absorbing aerosols, while the aerosol properties, modification, and mixing atmospheric processes differentiate along the IGP sites depending on the distance from the aerosol source, urban influence, and local characteristics.

A B S T R A C T Characteristics and emission budget of carbonaceous species from two distinct post-harvest agricultural-waste (paddy-and wheat-residue) burning emissions have been studied from a source region (Patiala: 30.28N, 76.38E; 250 m amsl) in the Indo-Gangetic Plain (IGP), Northern India. The PM 2.5 mass concentration varies from 60 to 390 mg m (3 during paddy-residue burning (OctoberÁNovember) with dominant contribution from organic carbon (OC:33%), whereas contribution from elemental carbon (EC) centres at Â4%. Watersoluble organic carbon (WSOC) accounts for about 50% of OC. In contrast, mass concentration of PM 2.5 during the period of wheat-residue burning (AprilÁMay) is significantly lower, varies from 18 to 123 mg m (3 and mass fractions of EC and OC are 7 and 26%, respectively. The diagnostic ratios of OC/EC (1192), WSOC/OC (0.5290.02), nss-K ' /OC (0.0690.00) and SPAHs/EC (4.390.7 mg/g) from paddy-residue burning emissions are significantly different than those from wheat-residue burning (OC/EC: 3.090.4; WSOC/OC: 0.6090.03; nss-K ' /OC: 0.1490.01 and SPAHs/EC: 1.390.2 mg/g). The emission budget of OC, EC and SPAHs from post-harvest agricultural-waste burning in the IGP are estimated to be 505968 Gg/y, 5992 Gg/y and 182932 Mg/y, respectively. From a global perspective, crop-residue burning in Northern India contributes nearly 20% of both OC and EC to the total emission budget from the agricultural-waste burning.

Impact of dust storms on the aerosol characteristics and radiative forcing over Patiala, northwestern India has been studied during April-June of 2010 using satellite observations and ground-based measurements. Six dust events (DE) have been identified during the study period with average values of Aqua-MODIS AOD 550 and Microtops-II AOD 500 over Patiala as 1.00 ± 0.51 and 0.84 ± 0.41, respectively while Aura-OMI AI exhibits high values ranging from 2.01 to 6.74. TheÅngström coefficients α 380−870 and β range from 0.12 to 0.31 and 0.95 to 1.40, respectively. The measured spectral AODs, the OPAC-derived aerosol properties and the surface albedo obtained from MODIS were used as main inputs in SBDART model for the calculation of aerosol radiative forcing (ARF) over Patiala. The ARF at surface (SRF) and top of atmosphere (TOA) ranges from ∼−50 to −100 Wm −2 and from ∼−10 to −25 Wm −2 , respectively during the maximum of dust storms. The radiative forcing efficiency was found to be −66 Wm −2 AOD −1 at SRF and −14 Wm −2 AOD −1 at TOA. High values of ARF in the atmosphere (ATM), ranging between ∼+40 Wm −2 and +80.0 Wm −2 during the DE days, might have significant effect on the warming of the lower and middle atmosphere and, hence, on climate over northwestern India.

We compare the mass concentrations of black carbon (BC) and elemental carbon (EC) from different emissions in the Indo-Gangetic Plain (IGP), using optical (Aethalometer; 880 nm) and thermooptical technique (EC-OC analyzer; 678 nm), respectively. The fractional contribution of BC mass concentration measured at two different channels (370 and 880 nm), OC/EC ratio, and non-sea-salt K+/EC ratios have been systematically monitored for representing the source characteristics of BC and EC in this study. The mass concentrations of BC varied from 8.5 to 19.6, 2.4 to 18.2, and 2.2 to 9.4 μg m−3during October-November (paddy-residue burning emission), December–March (emission from bio- and fossil-fuel combustion) and April-May (wheat-residue burning emission), respectively. In contrast, the mass concentrations of EC varied from 3.8 to 17.5, 2.3 to 8.9, and 2.0 to 8.8 μg m−3during these emissions, respectively. The BC/EC ratios conspicuously greater than 1.0 have been observed during paddy-residue burning emissions associated with high mass concentrations of EC, OC, and OC/EC ratio. The Ångström exponent (α) derived from Aethalometer data is approximately 1.5 for the postharvest agricultural-waste burning emissions, hitherto unknown for the IGP. The mass absorption efficiency (MAE) of BC and EC centers at ~1–4 m2 g−1and 2-3 m2 g−1during the entire study period in the IGP.

Atmospheric PM2.5 (particulate matter with aerodynamic diameter of ≤ 2.5 μm), collected from a source region [Patiala: 30.2 °N; 76.3 °E; 250 m above mean sea level] of emissions from post-harvest agricultural-waste (paddy-residue) burning in the Indo-Gangetic Plain (IGP), North India, has been studied for its chemical composition and impact on regional atmospheric radiative forcing. On average, organic aerosol mass accounts for 63% of PM2.5, whereas the contribution of elemental carbon (EC) is ∼3.5%. Sulphate, nitrate and ammonium contribute up to ∼85% of the total water-soluble inorganic species (WSIS), which constitutes ∼23% of PM2.5. The potassium-to-organic carbon ratio from paddy-residue burning emissions (KBB(+)/OC: 0.05 ± 0.01) is quite similar to that reported from Amazonian and Savanna forest-fires; whereas non-sea-salt-sulphate-to-OC ratio (nss-SO4(2-)/OC: 0.21) and nss-SO4(2-)/EC ratio of 2.6 are significantly higher (by factor of 5 to 8). The mass absorption efficiency of EC (3.8 ± 1.3 m(2) g(-1)) shows significant decrease with a parallel increase in the concentrations of organic aerosols and scattering species (sulphate and nitrate). A cross plot of OC/EC and nss-SO4(2-)/EC ratios show distinct differences for post-harvest burning emissions from paddy-residue as compared to those from fossil-fuel combustion sources in south-east Asia.