Possible climatic implications of high-altitude black carbon emissions

Abstract

Abstract. On account of its strong absorption of solar and terrestrial radiation, black carbon (BC) aerosol is known to impact large-scale systems, such as the Asian monsoon and the Himalayan glaciers, in addition to affecting the thermal structure of the lower atmosphere. While most studies focus on the near-surface abundance and impacts of BC, our study examines the implications of sharp and confined layers of high BC concentration (called elevated BC layers) at altitudes more than 4 km over the Indian region using the online regional chemistry transport model (WRF-Chem) simulations. These elevated BC layers were revealed in the recent in situ measurements using high-altitude balloons carried out on 17 March 2010, 8 January 2011 and 25 April 2011. Our study demonstrates that high-flying aircraft (with emissions from the regionally fine-tuned MACCity inventory) are the most likely cause of these elevated BC layers. Furthermore, we show that such aircraft-emitted BC can be transported to upper tropospheric or lower stratospheric heights ( ∼ 17 km) aided by the strong monsoonal convection occurring over the region, which is known to overshoot the tropical tropopause, leading to the injection of tropospheric air mass (along with its constituent aerosols) into the stratosphere. We show observational evidence for such an intrusion of tropospheric BC into the stratosphere over the Indian region using extinction coefficient and particle depolarisation ratio data from CALIOP Lidar on-board the CALIPSO satellite. We hypothesise that such intrusions of BC into the lower stratosphere and its consequent longer residence time in the stratosphere have significant implications for stratospheric ozone, especially considering the already reported ozone-depleting potential of BC.

Influence of the dry aerosol particle size distribution and morphology on the cloud condensation nuclei activation. An experimental and theoretical investigation

“…Several studies exist that characterize the CCN activity of soot particles generated in the exhaust of laboratory flames (Lambe et al, 2015) and commercial burners like the miniCAST (Henning et al, 2012;Friebel et al, 2019). Soot particle aging experiments are often performed in laboratory conditions that simulate the atmosphere and make use of flow reactors (Kotzick et al, 1997;Lambe et al, 2015;Zuberi et al, 2005) or atmospheric simulation chambers (Tritscher et al, 2011;Wittbom et al, 2014;Grimonprez et al, 2018). The hygroscopic properties of soot are generally determined at supersaturation conditions provided by instruments such as a variable supersaturation condensation nuclei counter (VSCNC) or a cloud condensation nuclei counter (CCNc).…”

“…Overall, freshly emitted soot particles are generally considered as poor CCN. However, several studies demonstrate that photochemical aging (Tritscher et al, 2011) or chemical aging that includes exposure to OH radicals (Zuberi et al, 2005;Lambe et al, 2015), O 3 (Kotzick et al, 1997;Wittbom et al, 2014;Grimonprez et al, 2018) or NO 3 radicals (Zuberi et al, 2005) under atmospheric relevant conditions can efficiently turn soot particles into CCN.…”

“…Only a few studies exist on the CCN activity of soot particles compared to non-aggregated aerosol particles (Grimonprez et al, 2018;Lambe et al, 2015;Sullivan et al, 2009;Tang et al, 2015). In these studies, a corrected volume equivalent diameter based on the estimated mass density of the soot particles is used to parameterize the particle size.…”

“…In these studies, a corrected volume equivalent diameter based on the estimated mass density of the soot particles is used to parameterize the particle size. However, particles characterized by very low activity like fresh soot particles have been reported to have κ < 0 ("apparent crossing of the Kelvin limit") in some instances (Grimonprez et al, 2018;Lambe et al, 2015;Tritscher et al, 2011). To avoid this problem, κ has been obtained from the fitting of the activation curve with generic sigmoid functions that do not take into account the particle size distribution or a distribution of values of κ.…”

Potential impact of carbonaceous aerosol on the upper troposphere and lower stratosphere (UTLS) and precipitation during Asian summer monsoon in a global model simulation

“…Satellite observations reveal transport of trace gases (CO, PAN, H 2 O, HCN) into the upper-level monsoon anticyclone by deep monsoon convection (Park et al, 2009;Randel et al, 2010;Kunze et al, 2010;Ploeger et al, 2011Ploeger et al, , 2012Ploeger et al, , 2013Fadnavis et al, 2014Fadnavis et al, , 2015Govardhan et al, 2017). Moreover, both back trajectory analysis based on CALIOP observations (Vernier et al, 2015) and modeling studies (Fadnavis et al, 2013) indicate that deep monsoon convection transports boundary layer aerosols into the upper troposphere and lower stratosphere (UTLS).…”