Widespread biomass burning smoke throughout the remote troposphere

Biomass burning emits ~34-41 Tg yr(-1) of smoke aerosol to the atmosphere. Biomass burning aerosol directly influences the Earth's climate by attenuation of solar and terrestrial radiation; however, its abundance and distribution on a global scale are poorly constrained, particularly after plumes dilute into the background remote troposphere and are subject to removal by clouds and precipitation. Here we report global-scale, airborne measurements of biomass burning aerosol in the remote troposphere. Measurements were taken during four series of seasonal flights over the Pacific and Atlantic Ocean basins, each with near pole-to-pole latitude coverage. We find that biomass burning particles in the remote troposphere are dilute but ubiquitous, accounting for one-quarter of the accumulation-mode aerosol number and one-fifth of the aerosol mass. Comparing our observations with a high-resolution global aerosol model, we find that the model overestimates biomass burning aerosol mass in the remote troposphere with a mean bias of >400%, largely due to insufficient wet removal by in-cloud precipitation. After updating the model's aerosol removal scheme we find that, on a global scale, dilute smoke contributes as much as denser plumes to biomass burning's scattering and absorption effects on the Earth's radiation field. Aerosol particles produced by biomass burning are ubiquitous in the remote troposphere, according to global airborne measurements over remote ocean regions.