Aerosol Climatology Over South and Southeast Asia: Aerosol Types, Vertical Profile, and Source Fields

Abstract

Aerosol climatology during typical haze dominating period over South and Southeast Asia was explored using several Earth-Observing A-Train satellite products retrieved in between 2010 and 2020. Comparatively high aerosol optical depth (AOD) with dominance of fine and UV-absorbing aerosols are noted across the Indo-Gangetic plain, South Asia (IGP; AOD: 0.58; UVAI: 0.74) against weak UV-absorbing fine aerosols over Southeast Asia (SEA; AOD: 0.26; UVAI: 0.07). Among inland IGP sites, decadal mean AOD resembles in Lahore (0.72 ± 0.45), Delhi (0.81 ± 0.46), Kanpur (0.84 ± 0.42), and Varanasi (0.78 ± 0.45); all exhibiting bimodal AOD distribution with a first peak in early November followed by a second in early January. In contrast, except mainland site Chiang Mai, all SEA maritime cities resemble in having typical September-October AOD peak, with the presence of fine and UV-neutral aerosols. Urban hotspots across IGP and SEA (except Dhaka, Chiang Mai) denote a spatially consistent minor increasing trend in AOD (0.2-1.8 × 10 −2 year −1) while increase in UVAI is more prominent over upper IGP. Dust aerosols dominate only in Karachi (46%) against strong UV-absorbing smoke aerosols over rest of the IGP (71-91%), and UV-neutral smoke aerosols across SEA (84-92%). Vertical stratification of aerosol types is noted across IGP as in lower atmosphere (<4 km) polluted dust/urban aerosols remain abundant, with gradual decrease in dust aerosols from upper to lower IGP and consequent increase in smoke aerosols. At upper atmosphere (>4 km), however, dust aerosols clearly dominate. Over SEA, smoke are the most abundant aerosols across the atmospheric column followed by polluted dust. No evidence of intracontinental transport of aerosols from IGP to Southeast Asia or vice versa is, however, noted. Plain Language Summary Aerosol climatology during typical haze dominating period over two global aerosol hotspots: South and Southeast Asia was explored using several satellite-based aerosol optical properties retrieved using Earth Observing A-Train satellites (Aqua, Aura, CALIPSO). Comparatively high aerosol optical depth with dominance of fine and absorbing aerosol are noted across the Indo-Gangetic plain, South Asia against weak absorbing fine particles over Southeast Asia. Presence of strong absorbing aerosol over Indo-Gangetic plain may have greater implications on regional climate. We note absorbing dust aerosols only over Karachi against strong absorbing smoke aerosols over Lahore, Delhi, Kanpur, Varanasi, and Dhaka, and UV-neutral smoke aerosols over Singapore, Penang, and Kuala Lumpur. Vertical stratification of aerosol types is also noted across IGP as in lower atmosphere (<4km) polluted dust/ polluted urban aerosol remains abundant, with gradual decrease in dust aerosols from upper to lower IGP and consequent increase in smoke aerosols. No evidence in intracontinental transport of smoke aerosols is found, as biomass burning emissions over upper IGP, Kalimantan, and Sumatra primarily modulating climatology of regional aerosols. BAN...

Sources, Composition, and Mixing State of Submicron Particulates over the Central Indo-Gangetic Plain

“…18,19 Studies on submicron particulate chemistry and sources are sparse over South Asia, constrained especially by the limitation and uncertainty in PM 1 measurement. Within South Asia, the Indo-Gangetic Plain (IGP) shares the maximum burden of particulate pollution; 20,21 particulates which are reported to be highly mixed, 22−24 composed primarily of organics and secondary inorganics 13,25−27 with diverse kinds of sources. 28,29 Until the submission of the manuscript, very few studies explored submicron particulate chemistry over the IGP, focusing mainly over the urban agglomerates with emphasis on particulate composition and sources, 30 influence of fog processing, 13 and formation of secondary organics.…”

“…Studies on submicron particulate chemistry and sources are sparse over South Asia, constrained especially by the limitation and uncertainty in PM 1 measurement. Within South Asia, the Indo-Gangetic Plain (IGP) shares the maximum burden of particulate pollution; , particulates which are reported to be highly mixed, − composed primarily of organics and secondary inorganics ,− with diverse kinds of sources. , Until the submission of the manuscript, very few studies explored submicron particulate chemistry over the IGP, focusing mainly over the urban agglomerates with emphasis on particulate composition and sources, influence of fog processing, and formation of secondary organics. , These studies essentially focus on season- or event-specific aerosol chemistry with none explicitly considering particulate exposure data for a longer period. Besides, very few studies explored submicron particulate morphology and mixing state leaving considerable uncertainties about their possible climate and health implications.…”

Effects of Atmospheric Aerosol Types on Ultraviolet Flux at Different Stations in the Indo-Gangetic Plain

“…Increasing industrialization has led to an increase in anthropogenic activities, leading to consistent increases in aerosol over the region (it became the global hub for intense aerosol loading) [5,6]. Many studies have shown an implication of different aerosol particles over the region, but the interaction and effects of the pertaining aerosol types on UVA and UVB radiation have still been lacking in the long term [7][8][9][10]. The present study on the effect of distinct aerosol types on UVA and UVB at different stations of IGP tries to fill the existing gap to some extent.…”

Integrated Remote Sensing Observations of Radiative Properties and Sources of the Aerosols in Southeast Asia: The Case of Thailand

“…The high aerosol levels have adversely affected human health, visibility, and the climate. There is a diversity of aerosol types in this region, including organic carbon, black carbon, mineral dust, and sea salt, and interactions between these aerosols further complicates the understanding of their properties and their radiative forcing potentials [4][5][6]. The climate in this region is influenced by monsoon systems, resulting in distinct wet and dry seasons, which significantly influence aerosol production and transport.…”

“…Satellite observations provide strong connections between hot spots and pollution plumes, or between urban land cover and heat island zones. Some satellite sensors, such as the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), provide aerosol vertical profiles beneficial for the identification of aerosol types and sources [6]. Furthermore, ground-based remote sensing, such as AERONET, is typically used to validate satellite products.…”