Evaluation of Sulfate and Organic Aerosol in the Global UTLS: Budget and Size Distribution

Stratospheric sulfate and organic aerosols account for 20% of the total direct aerosol radiative forcing since 1850 [Yu et al., 2016]. Limited in-situ measurements on aerosol composition have been made in the upper troposphere and lower stratosphere (UTLS), mostly in the Northern Hemispheric mid-latitudes and tropics [Froyd et al., 2009; Murphy et al., 2014; Liao et al., 2015]. Based on those measurements and recent modeling studies [Yu et al., 2015a, 2015b, 2016], organic material commonly contributes half of the aerosol mass in the UTLS in the North Hemisphere. We summarize the global UTLS aerosol mass, size distribution and composition using in-situ measurements over the past 15 years including NASA SEAC4RS in 2013 [Liao et al., 2015; Yu et al., 2015a; Toon et al., 2016], NASA ATom in 2016 and 2017, NASA AVE in 2004 and 2006 [Froyd et al., 2009] and a balloon-borne campaign from Kunming in 2015 [Yu et al., 2017]. The most recent aerosol measurements on sulfate, organics, and their size distributions from the NASA ATom deployments provide a global view of upper tropospheric aerosol composition over remote regions (i.e. the Pacific and Atlantic oceans) in both hemispheres. These in-situ measurements are compared with a sectional aerosol model coupled with the NCAR Community Earth System Model (CESM-CARMA). The comparisons and simulations demonstrate the importance of UTLS aerosols on aerosol-radiation-climate interactions, and highlight the need for a better understanding on the UTLS aerosols' budget, sources, seasonal cycle, transport pathways and linkage to climate change. References:Froyd et al. (2009), Atmospheric Chemistry and Physics, 9(13), 4363-4385. Liao et al. (2016), J. Geophys. Res. Atmos., 120, 2990-3005. Murphy et al. (2014), Q.J.R. Meteorol. Soc., 140: 1269-1278 Toon, O. B. et al. (2016) , J. Geophys. Res. Atmos., 121, 4967-5009 Yu, P. et al. (2015a), J. Adv. Model. Earth Syst., 7, 865-914 Yu, P. et al. (2015b), Geophys. Res. Lett., 42, 2540-2546 Yu, P. et al. (2016), Geophys. Res. Lett., 43, 9361-9367 Yu, P. et al. (2017), , Proc. Natl. Acad. Sci., 114 (27) 6972-6977