Two heavy haze events over Lumbini in southern Nepal: Enhanced aerosol radiative forcing and heating rates. (1st September 2020)

• Record Type: Journal Article
• Authors: Rupakheti, Dipesh; Kang, Shichang; Rupakheti, Maheswar
• Is Part Of: Atmospheric environment. Volume 236(2020)
• Publication Date: 2020-09-01
• Subjects: Haze events -- Aerosol optical properties -- Radiative forcing -- AERONET -- Lumbini; Air -- Pollution -- Periodicals; Air -- Pollution -- Meteorological aspects -- Periodicals; 551.51
• DOI: 10.1016/j.atmosenv.2020.117658
• Languages: English
• ISSNs: 1352-2310

Abstract

Abstract: 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 Ångström 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. Graphical abstract: Image 1 Highlights: Investigation of aerosol optical properties over a World Heritage Site during haze events. Instantaneous AOD exceeded 3.0 whereas daily AOD was above 2.0. AOD levels were ~300% and ~230% higher compared to the average AOD during 2013–2014. High amount of aerosol radiative forcing and resultant high heating rate. Volume concentration in fine mode was 3–5 times higher during the haze events.