Evaluation of factors controlling long-range transport of black carbon to the Arctic

Abstract

[1] This study evaluates the sensitivity of long-range transport of black carbon (BC) from midlatitude and high-latitude source regions to the Arctic to aging, dry deposition, and wet removal processes using the Geophysical Fluid Dynamics Laboratory (GFDL) coupled chemistry and climate model (AM3). We derive a simple parameterization for BC aging (i.e., coating with soluble materials) which allows the rate of aging to vary diurnally and seasonally. Slow aging during winter permits BC to remain largely hydrophobic throughout transport from midlatitude source regions to the Arctic. In addition, we apply surface-dependent dry deposition velocities and reduce the wet removal efficiency of BC in ice clouds. The inclusion of the above parameterizations significantly improves simulated magnitude, seasonal cycle, and vertical profile of BC over the Arctic compared with those in the base model configuration. In particular, wintertime concentrations of BC in the Arctic are increased by a factor of 100 throughout the tropospheric column. On the basis of sensitivity tests involving each process, we find that the transport of BC to the Arctic is a synergistic process. A comprehensive understanding of microphysics and chemistry related to aging, dry and wet removal processes is thus essential to the simulation of BC concentrations over the Arctic.

Sensitivity of remote aerosol distributions to representation of cloud–aerosol interactions in a global climate model

“…Slower BC aging by itself causes a substantial increase in global BC burden. Both ALL m7 and CONV m7 have BC burdens (0.16-0.17 Tg C) and lifetimes (7.5-7.9 days) that are close to some previous studies (e.g., Textor et al, 2007;Koch et al, 2009b;Liu et al, 2011a) that used similar BC emission inventories. In comparison, the ALL m3 (no BC aging but other improvements) has 37 % smaller burden and lifetime.…”

“…There are also many uncertainties in BC surface measurements (e.g., Shindell et al, 2008;Koch et al, 2009b;Vignati et al, 2010), which may explain part of the discrepancy, but there is likely more room for improvement in the long-range-transport-related processes in the CAM5 (e.g., Ma et al, 2013) and in the aerosol emission inventories used for the simulations . The global annual BC emissions for the year 2000 are about 7.8 Tg C yr −1 , which is on the lower side of the range used by a variety of global models -for example, the diverse BC emission rates used by the AeroCom model intercomparison study range from 7.5 to 19 Tg C yr −1 Liu et al, 2011a), indicating large uncertainties in BC emission inventory. Bond et al (2004) used bottom-up estimates of uncertainties in source strength to show that global annual BC emissions could range between 4.3 and 22 Tg C yr −1 .…”

“…Regarding aerosol wet removal during the transport to remote regions, modeling studies have shown that chemical and physical transformations (i.e., aging processes that transform particles from a mostly hydrophobic state upon emission to a more hydrophilic state) can be also very important (e.g., Vignati et al, 2010;Liu et al, 2011a). Condensation of soluble material (e.g., sulfuric acid gas and condensable organics), coagulation with soluble particles and oxidation of organic material can be involved in aging, but uncertainties remain (Pöschl et al, 2001;Riemer et al, 2004).…”

Source Sector and Region Contributions to Black Carbon and PM<sub>2.5</sub> in the Arctic

“…Regional chemical transport models with a focus on the Arctic capture the BC concentration better over the Arctic. Koch et al 2009 andLiu et al, 2011 studies captured the NASA ARCTAS flights vertical profiles and seasonality well.…”

Development of a parameterization of black carbon aging for use in general circulation models

“…(7) given by Riemer et al (2004) during nighttime) will be applicable only for a polluted region over land (e.g., Germany). Recently, Liu et al (2011) developed a parameterization of BC aging using a function of hydroxyl (OH) radical concentration, defined as follows:…”