Characteristics, sources, and transport of aerosols measured in spring 2008 during the aerosol, radiation, and cloud processes affecting Arctic Climate (ARCPAC) Project

摘要

We present an overview of the background, scientific goals, and execution ofthe Aerosol, Radiation, and Cloud Processes affecting Arctic Climate(ARCPAC) project of April 2008. We then summarize airborne measurements,made in the troposphere of the Alaskan Arctic, of aerosol particle sizedistributions, composition, and optical properties and discuss the sourcesand transport of the aerosols. The aerosol data were grouped into fourcategories based on gas-phase composition. First, the background tropospherecontained a relatively diffuse, sulfate-rich aerosol extending from the topof the sea-ice inversion layer to 7.4 km altitude. Second, a region ofdepleted (relative to the background) aerosol was present within the surfaceinversion layer over sea-ice. Third, layers of dense, organic-rich smokefrom open biomass fires in southern Russia and southeastern Siberia werefrequently encountered at all altitudes from the top of the inversion layerto 7.1 km. Finally, some aerosol layers were dominated by componentsoriginating from fossil fuel combustion.Of these four categories measured during ARCPAC, the diffuse backgroundaerosol was most similar to the average springtime aerosol propertiesobserved at a long-term monitoring site at Barrow, Alaska. The biomassburning (BB) and fossil fuel layers were present above the sea-ice inversionlayer and did not reach the sea-ice surface during the course of the ARCPACmeasurements. The BB aerosol layers were highly scattering and weremoderately hygroscopic. On average, the layers produced a noontime netheating of ~0.1 K day−1 between 3 and 7 km and a slightcooling at the surface. The ratios of particle mass to carbon monoxide (CO)in the BB plumes, which had been transported over distances >5000 km, werecomparable to the high end of literature values derived from previousmeasurements in wildfire smoke. These ratios suggest minimal precipitationscavenging and removal of the BB particles between the time they wereemitted and the time they were observed in dense layers above the sea-iceinversion layer.