UC San Diego

Black carbon (BC), a main component of combustion- generated soot, is a strong absorber of sunlight and contributor to climate change. This dissertation is divided into three separate sections. Part one presents estimates of long range transport of black carbon (BC) and aerosol fine mass across the Pacific Ocean into North America during April 2004. The BC and aerosol transport estimates were based on simulations by the CFORS (Chemical weather FORecast System) model. Model validation was accomplished using aircraft data and surface measurements of fine mass and BC at 30 IMPROVE (Interagency Monitoring of Protected Visual Environments) ground observatories located in the Western United States. The transported BC mass at 130⁰W in the spring of 2004 amounted to approximately 77% of the total BC emitted in North America during the same period. The second section highlights a new analysis method for measuring BC particles in snow and rain water. This includes a description of the development of a laboratory standard of known amounts of BC in water, evaluation of sample filtration efficiency, and modifications to the thermal-optical analysis method (TOA), developed specifically for this research in order to make accurate measurements of BC in snow and rain water. Changes in the wavelength dependence of absorption during TOA are used to separate BC from charring organics, yielding a more accurate measurement of BC mass on the filter. The final section of this dissertation presents the first measurements BC deposition in rain and snow in California, as well as a general estimate of contribution from Asian BC. The average BC concentration in coastal rain was 5 ng/g, and slightly higher in the mountain snow, at 6 ng/g and 7 ng/g. The data revealed that snow was able to efficiently remove almost all of the atmospheric BC to the snowpack. Measurements of aerosol elemental composition, combined with meteorological data and calculated air mass back trajectories, indicated that transported Asian aerosols contribute as much as 40% to the observed BC in California's mountains and therefore in the snow pack as well