Analysis of transpacific transport of black carbon during HIPPO-3: implications for black carbon aging

Abstract

Abstract. Long-range transport of black carbon (BC) is a growing concern as a result of the efficiency of BC in warming the climate and its adverse impact on human health. We study transpacific transport of BC during HIPPO-3 using a combination of inverse modeling and sensitivity analysis. We use the GEOS-Chem chemical transport model and its adjoint to constrain Asian BC emissions and estimate the source of BC over the North Pacific. We find that different sources of BC dominate the transport to the North Pacific during the southbound (29 March 2010) and northbound (13 April 2010) measurements in HIPPO-3. While biomass burning in Southeast Asia (SE) contributes about 60 % of BC in March, more than 90 % of BC comes from fossil fuel and biofuel combustion in East Asia (EA) during the April mission. GEOS-Chem simulations generally resolve the spatial and temporal variation of BC concentrations over the North Pacific, but are unable to reproduce the low and high tails of the observed BC distribution. We find that the optimized BC emissions derived from inverse modeling fail to improve model simulations significantly. This failure indicates that uncertainties in BC removal as well as transport, rather than in emissions, account for the major biases in GEOS-Chem simulations of BC over the North Pacific.The aging process, transforming BC from hydrophobic into hydrophilic form, is one of the key factors controlling wet scavenging and remote concentrations of BC. Sensitivity tests on BC aging (ignoring uncertainties of other factors controlling BC long range transport) suggest that in order to fit HIPPO-3 observations, the aging timescale of anthropogenic BC from EA may be several hours (faster than assumed in most global models), while the aging process of biomass burning BC from SE may occur much slower, with a timescale of a few days. To evaluate the effects of BC aging and wet deposition on transpacific transport of BC, we develop an idealized model of BC transport. We find that the mid-latitude air masses sampled during HIPPO-3 may have experienced a series of precipitation events, particularly near the EA and SE source region. Transpacific transport of BC is sensitive to BC aging when the aging rate is fast; this sensitivity peaks when the aging timescale is in the range of 1-1.5 d. Our findings indicate that BC aging close to the source must be simulated accurately at a process level in order to simulate better the global abundance and climate forcing of BC.

How shorter black carbon lifetime alters its climate effect

“…Constraining the BC towards observed BC vertical profiles (as in our LIFETIME simulation) reduces the direct aerosol effect closer to the lower range of AeroCom Phase II models. This study should initiate new efforts to derive best estimates of BC RF in multi-model studies with constraints from observations on BC lifetime 3,5,30 and community effort on improved BC emissions.…”

In situ measurements of water uptake by black carbon‐containing aerosol in wildfire plumes

“…Despite this importance, the processes governing the lifetime and distribution of BC in the atmosphere remain poorly characterized. Several recent papers have highlighted the difficulty of modeling BC loadings in the remote atmosphere [ Schwarz et al ., , ; Shen et al ., ; Wang et al ., ], which has been attributed, in part, to parameterization of BC removal. The modeled atmospheric lifetime of BC is highly sensitive to uncertainties in both the amount of non‐refractory material internally mixed with BC (here referred to generically as “coatings”) and interactions of BC‐containing aerosol with water in the atmosphere.…”

Individual particle morphology, coatings, and impurities of black carbon aerosols in Antarctic ice and tropical rainfall

“…BC emissions may have already contributed to large-scale changes in atmospheric circulation, with models suggesting that the Northern Hemisphere tropics expand linearly with increasing radiative forcing from BC emissions [Kovilakam and Mahajan, 2015]. The physical, chemical, and optical properties of BC are dynamic and evolve during atmospheric transport [Browne et al, 2015;Shen et al, 2014;Wang et al, 2014]. Estimates of BC climate sensitivity are complicated by hemispheric differences in both emission sources (fossil fuels or biomass burning) and coemitted chemical species, which coat and react with BC in the atmosphere.…”