Single particle characterization of black carbon aerosol in the Northeast Tibetan Plateau, China

Black carbon (BC), a byproduct of incomplete combustion, is the most efficiently light-absorbing aerosol component in the atmosphere. BC plays a major role in climate change and is the second largest contributor to anthropogenic radiative forcing after CO₂. Due to its more non-uniform spatiotemporal distribution, BC induces more dramatic regional forcing than either CO₂ or methane. A single particle soot photometer and a CO instrument were deployed at Qinghai Lake in the Northeast Tibetan Plateau on 10/16-27/2011 characterize refractory black carbon (rBC) mass size distribution and mixing state, and the relationships of rBC loading to CO mass mixing ratio. The area had an average measured rBC mass concentration of 0.36 μg STP/cu m. rBC concentration peaked at night with low concentrations in the afternoon. This diurnal cycle was loosely anti-correlated with the mixed layer depth, consistent with trapping of local emissions at night, and increased ventilation during the day. Measurements in the late afternoon and early evening, when the mixed layer depths were the highest, were representative of the larger Tibetian Plateau region with an average rBC concentration of 0.23 μg STP/cu m. A lognormal primary mode with MMD of ∼175-nm and a small secondary lognormal mode with MMD of 470-500 nm (volume-equivalent diameter assuming 2 g/cu cm void free density) were observed. Relative reduction in the secondary mode during a snow event supported recent work suggesting size dependent removal of BC by precipitation. rBC was strongly correlated with CO, with different correlation slopes depending on air mass and local wet deposition. The data improved sampling of as yet poorly understood features of rBC aerosol in China and strengthened conclusions about size dependent removal of BC via precipitation. This is an abstract of a paper presented at the 106th AWMA Annual Conference and Exhibition (Chicago, IL 6/25-28/2013).