Size-Resolved Particle and Black Carbon Deposition Over the Cryosphere

Abstract

Aerosols are small liquid or solid particles suspended in the atmosphere, and are the strongest driver of uncertainties in understanding climate. Wet and dry deposition are the key processes that remove aerosols from the atmosphere – and thus control their concentration and lifetime in the atmosphere. Presently, there are serious problems with the existing understanding of depositions rates, stemming from the lack of direct measurements. Black carbon is one type of aerosol that is particularly important as it is a short-lived climate forcer, and its deposition to the cryosphere (surfaces covered by snow or ice) increases absorption of sunlight by the surface, enhancing snow aging and melting and generating positive climate feedbacks.

There is a clear need for additional observational constraints and investigation of aerosol deposition, including measurements of black carbon, which we propose to address by performing the first unambiguous direct eddy flux covariance measurements of both total and black carbon aerosol dry deposition over the cryosphere. By measuring black carbon concentration and size in the snow, we will distinguish wet removal rates for this species from dry rates. We propose measurements of total and black carbon deposition at two sites – first a local site in Colorado that will allow us to optimize measurement approaches and investigate snow-covered forested areas, and the Department of Energy Atmospheric Radiation Measurement (ARM) Mobile Facility at the Oliktok Point site on the North Slope of Alaska. The Alaska site is particularly relevant to understanding anthropogenic influences on the remote Arctic.

We will compare our measurements to model parameterizations to constrain uncertainties and systematic bias, and improve deposition parameterizations. We will assess the possibility for achieving full deposition budget closure using snow measurements of black carbon. This work will fundamentally improve understanding of aerosol removal processes from the atmosphere over the cryosphere.