Total suspended particles (TSP) were collected in Lumbini from April 2013 to March 2016 to better understand the characteristics of carbonaceous aerosol (CA) concentrations, compositions and sources and their light absorption properties in rural region of severe polluted Indo-Gangetic Plain (IGP). Extremely high TSP (203.9 +/- 109.6 mu g m(-3)), organic carbon (OC 32.1 +/- 21.7 mu g m(-3)), elemental carbon (EC 6.44 +/- 3.17 mu g m(-3)) concentrations were observed in Lumbini particularly during winter and post-monsoon seasons, reflecting the combined influences of emission sources and weather conditions. SO42- (7.34 +/- 4.39 mu g m(-3)) and Ca2+ (5.46 +/- 5.20 mu g m(-3)) were the most dominant anion and cation in TSP. These components were comparable to those observed in urban areas in South and East Asia but significantly higher than those in remote regions over the Himalayas and Tibetan Plateau, suggesting severe air pollution in the study region. Various combustion activities including industry, vehicle emission, and biomass burning are the main reasons for high pollutant concentrations. The variation of OC/EC ratio further suggested that biomass such as agro-residue burning contributed a lot for CA, particularly during the non-monsoon season. The average mass absorption cross- of EC (MAC(EC)) and water-soluble organic carbon (MAC(WSOC)) were 7.58 +/- 3.39 and 1.52 +/- 0.41 m(2) g(-1), respectively, indicating that CA in Lumbini was mainly affected by local emissions. Increased biomass burning decreased MAC(EC); whereas, it could result in high MAC(WSOC) during the non-monsoon season. Furthermore, dust is one important factor causing higher MAC(WSOC) during the pre-monsoon season.

The Indo-Gangetic Plain (IGP) suffers from recurrent heavy air pollution during the dry season of each year. The AERONET station established in Lumbini, a semi-urban site and historically significant location as the birthplace of Buddha in the northern edge of the central IGP in Nepal, captured two events of heavy air pollution: 29-30 October (Event-I) and 1-2 December (Event-II) of 2014. Daily aerosol optical depth (AOD) was found to be 2.66, 2.44, 2.09 and 2.15 respectively with angstrom ngstrom exponent (AE) > 1 during both events. The daily AOD during two events was 3.26-4.43 times higher than average AOD observed during the monitoring period 2013-2014. Based on various aerosol parameters we concluded that the fine-mode aerosols sourced from biomass-burning and urban/industrial activities were responsible for the haze events. Aerosol absorbed 205-240 Wm(-2) of the solar radiation in the atmosphere, resulting in aerosol-induced atmospheric heating rate of 5.76-7.28 K day(-1) during the hazy days. Back-trajectory analysis of air masses reaching Lumbini showed that the air masses either originated or travelled over the regions with open fires both prior and during the events. In addition to this, meteorological conditions (e.g. prevailing winds) also played role in initiation/persistence of the haze events.