Exposure to ambient black carbon derived from a unique inventory and high-resolution model

Black carbon (BC) is increasingly recognized as a significant air pollutant with harmful effects on human health, either in its own right or as a carrier of other chemicals. The adverse impact is of particular concern in those developing regions with high emissions and a growing population density. The results of recent studies indicate that BC emissions could be underestimated by a factor of 2–3 and this is particularly true for the hot-spot Asian region. Here we present a unique inventory at 10-km resolution based on a recently published global fuel consumption data product and updated emission factor measurements. The unique inventory is coupled to an Asia-nested (∼50 km) atmospheric model and used to calculate the global population exposure to BC with fully quantified uncertainty. Evaluating the modeled surface BC concentrations against observations reveals great improvement. The bias is reduced from −88% to −35% in Asia when the unique inventory and higher-resolution model replace a previous inventory combined with a coarse-resolution model. The bias can be further reduced to −12% by downscaling to 10 km using emission as a proxy. Our estimated global population-weighted BC exposure concentration constrained by observations is 2.14 μg⋅m⁻³; 130% higher than that obtained using less detailed inventories and low-resolution models.Black carbon (BC), or soot, emitted from incomplete combustion of carbonaceous fuels is an air pollutant which also plays an important role in climate change (1). BC is an indicator of air particulate pollution and BC in ambient air has an impact on human health (2). In a recent study in China, it was found that the effects of BC on morbidity appear to be more robust than the effects of fine particles in general (3, 4).However, global atmospheric aerosol models often underestimate the concentration of BC at the surface, particularly over Asia, by a factor that typically ranges from 2 to 10 (5–7). In one study, the observed BC surface concentration for China could only be reproduced by doubling the emissions prescribed to a transport model (8). It is often argued that the underestimation is due to a low bias in BC emission inventories, suggesting a need to revisit these previous inventories (9).In a bottom-up approach, BC emission is estimated based on the amount of fuel consumed and an emission factor (EF_BC, defined as the amount of BC emitted per unit mass of fuel consumed) for each of various combustion sources. For previous inventories, the lack of EF_BC measurements in developing countries led to high uncertainty in estimating the total emissions (10). In addition, the use of fuel data at the national level is likely to distort the geographical distribution of emissions within large countries such as China and India (11). Recently, a 0.1° × 0.1° fuel database with 64 types of combustion has been developed based on local or national fuel consumption statistics. This database improves the resolution of the spatial distribution of emissions for large countries (12). To fill the data gap in developing countries, a set of EF_BC values has been compiled for various residential solid fuel combustion devices and vehicles (13–20). In addition to the problems with the emission inventories, the coarse resolution of existing global aerosol models also hinders our ability to capture detailed spatial variation, leading to poor agreement between model prediction and observations (7).In this study we develop and evaluate a unique global BC emission inventory using a zoomed aerosol model, and estimate the global population’s exposure to BC with a focus on Asia. The influence of model resolution and the use of an updated emission inventory on the calculated BC concentration are evaluated against field observations.