Observation-constrained atmospheric lifetime and emission fluxes of black carbon aerosols over South Asia

• Black carbon (BC) aerosols cause climate perturbation and affect air quality/human health. In densely populated South Asia—where the warming effect of BC is estimated to be ~ orders of magnitude higher than the global average—model simulations underestimate the wintertime atmospheric abundance of BC relative to surface observations. Two possible explanations for this model-observation offset are ill-constrained regional emission fluxes and atmospheric BC lifetime  (τBC). Here, we combine hourly-resolved BC and carbon monoxide (CO) measurements for three successive winters from a South Asian receptor site—the Maldives Climate Observatory at Hanimaadhoo (MCOH)—in inverse frameworks, to assess the impact of emissions fluxes and lifetimes on ambient BC concentrations. The average ΔBC/ΔCO ratio (background corrected) at MCOH of 14±5 ng m-3 ppb-1 is found to be 2-3 times higher than in the East Asian outflow (range: 2 to 8 ng m-3 ppb-1). A BC transport efficiency of ~86% suggests low influence of wet scavenging processes during the dry South Asian winter period. Using statistical time series analysis, the τBC for dry wintertime South Asia is estimated to be 8±0.5 days, which is higher than commonly used in models. By coupling air mass back trajectories, lifetimes, and the ΔBC/ΔCO time-series data within an inverse modelling framework, we provide an observation-based “top-down” BC emission flux for South Asia estimated to be ~2.4±1 Tg/year. This is significantly higher than estimates from current “bottom-up” emission inventories (EIs). Taken together, this study suggests  that to reconcile long-standing BC model-observation offsets in South Asia, existing emission estimates may need to be more than doubled in magnitude.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences (hsv//eng)

Nyckelord

atmosfärvetenskap och oceanografi

Atmospheric Sciences and Oceanography

Publikations- och innehållstyp

vet (ämneskategori)

ovr (ämneskategori)