Wintertime aerosol characteristics over the Indo‐Gangetic Plain (IGP): Impacts of local boundary layer processes and long‐range transport

Abstract

[1] The Indo-Gangetic Plain (IGP) encompasses a vast area, (accounting for $21% of the land area of India), which is densely populated (accommodating $40% of the Indian population). Highly growing economy and population over this region results in a wide range of anthropogenic activities. A large number of thermal power plants (most of them coal fed) are clustered along this region. Despite its importance, detailed investigation of aerosols over this region is sparse. During an intense field campaign of winter 2004, extensive aerosol and atmospheric boundary layer measurements were made from three locations: Kharagpur (KGP), Allahabad (ALB), and Kanpur (KNP), within the IGP. These data are used (1) to understand the regional features of aerosols and BC over the IGP and their interdependencies, (2) to compare it with features at locations lying at far away from the IGP where the conditions are totally different, (3) to delineate the effects of mesoscale processes associated with changes in the local atmospheric boundary layer (ABL), (4) to investigate the effects of long-range transport or moving weather phenomena in modulating the aerosol properties as well as the ABL characteristics, and (5) to examine the changes as the season changes over to spring and summer. Our investigations have revealed very high concentrations of aerosols along the IGP, the average mass concentrations (M T ) of total aerosols being in the range 260 to 300 mg m À3 and BC mass concentrations (M B ) in the range 20 to 30 mg m À3 (both $5 to 8 times higher than the values observed at off-IGP stations) during December 2004. Despite, BC constituted about 10% to the total aerosol mass concentration, a value quite comparable to those observed elsewhere over India for this season. The dynamics of the local atmospheric boundary layer (ABL) as well as changes in local emissions strongly influence the diurnal variations of M T and M B , both being inversely correlated with the mixed layer height (Z i ) and the ventilation coefficient (V c ). The share of BC to total aerosols is highest ($12%) during early night and lowest ($4%) in the early morning hours. While an increase in the V c results in a reduction in the concentration almost simultaneously, an increase in Z imax has its most impact on the concentration after $1 day. Accumulation mode aerosols contributed $90% to the aerosol concentration at ALB, $77 % at KGP and 74% at KNP. The BC mass mixing ratio was $10% over all three locations and is comparable to the value reported for Trivandrum, a tropical coastal location in southern India. This indicates presence of submicron aerosols species other than BC (such as sulfate) over KGP and KNP. A cross-correlation analysis showed that the changes in M B at KGP is significantly correlated with those at KNP, located $850 km upwind, and ALB after a delay of $7 days, while no such delay was seen between ALB and KNP. Back trajectory analyses show an enhancement in M B associated with trajectories arriving from west, the farther from to the west they arr...

Seasonal Characteristics of Aerosol Black Carbon in Relation to Long Range Transport over Tripura in Northeast India

“…From different literature, it is clear that all the available methods for measurement of EBC mass concentration are based on some assumptions that are instrument specific, site specific and also depends on the type of carbonaceous aerosol, and its fraction to the total aerosol mass (Weingartner et al, 2003;Hitzenberger et al, 2006;Moorthy et al, 2007;Nair et al, 2007). So there is no standard method that gives unique value of EBC concentration for a particular location.…”

“…Thus in situ measurement of black carbon at such station has its own importance. Even though, several studies on short as well as long term properties of EBC and source impact over the Indian region are available (e.g., Satheesh and Ramanathan, 2000;Nair et al, 2007;Beegum et al, 2009 etc. ), the study of EBC over the northeastern part of India is scarce other than that reported long-term properties of EBC from Dibrugarh (Pathak et al, 2010).…”

Carbonaceous and Secondary Inorganic Aerosols during Wintertime Fog and Haze over Urban Sites in the Indo-Gangetic Plain

“…In addition, lower boundary layer height (~500-800 m) (Nair et al, 2007) and prevailing meteorological conditions (lower temperature and calm winds, and high relative humidity) are conducive to the accumulation of aerosol and pollutants in the lower atmosphere over the IGP. The sampling period was also characterized by a number of fog and haze weather conditions in the Gangetic Plain (Ramachandran et al, 2006;Lal et al, 2008).…”

“…Recent studies suggest that a significant fraction of atmospheric particulate matter (PM) in the Indo-Gangetic Plain are comprised of carbonaceous aerosol (~30-35% of the PM) and water-soluble inorganic species (~10-20% of the PM) over IGP and other locations in India Rengarajan et al, 2007;Ram et al, 2010a;Deshmukh et al, 2011;Kothai et al, 2011). During the wintertime, low ambient temperatures (range: ~10-20°C, at times dipping as low as 5°C) and weak winds (< 2 m/s) and boundary layer height (~500-800 m) favour stable atmosphere, leading to poor convective mixing and accumulation of pollutants in the lower atmosphere (Nair et al, 2007;Ram et al, 2010a).…”

CCN closure study: Effects of aerosol chemical composition and mixing state

“…Kanpur has a population of more than 4.5 million (1452 people/km 2 ), and the sampling site is located ∼12 km northwest of the city center [Kanawade et al, 2014]. The major pollution sources in the winter season are vehicle emissions, industrial emissions, biomass burning, open area burning, coal power plants, and domestic cooking [Nair et al, 2007]. In addition, the site is also affected by long-range transported aerosols from the northwestern part of India, which experiences large numbers of forest fires [Patidar et al, 2012].…”