Observations of plumes containing gaseous mercury from point sources in the Los Angeles Basin during the 2010 CalNex ship cruise

Mercury is a neurotoxin with both natural and anthropogenic sources to the atmosphere, where it can be transported long distances and potentially impact pristine locations. California has few anthropogenic sources relative to total U.S. emissions, however, many of the sources are located in the Los Angeles Basin including oil refineries and an incinerator. During the spring of 2010 (May 14-June 8) the research vessel Atlantis sailed in the San Pedro harbor and other locations along the Southern California coastline. Simultaneous measurements of total gaseous mercury (TGM), CO2, CO, NOx, SO2, O3, and meteorology were made. These data revealed a number of plume events with elevated TGM concentrations simultaneous with elevated CO2, CO, and other species indicating anthropogenic point sources. The slope of a linear regression between two species during a plume event is called an enhancement ratio (ER), which can be an approximation of the ratio of emissions of these species at the source of the plume. Four plume events likely originated from local oil refineries based on the ship’s position and wind direction and were characterized by mean ERs of 5.2 x 10-7, 2.0 x 10-6, and 3.1 x 10-5 mol mol-1 for TGM/CO, TGM/NOx, and TGM/SO2 respectively. Estimates of emissions ratios from five refineries in harbor area were 4.5 x 10-6, 8.0 x 10-6, and 2.2 x 10-5 for TGM/CO, TGM/NO2, and TGM/SO2 respectively. Compared with measured ERs, emissions estimates are thus 9x and 4x times higher for TGM/CO and TGM/NO2, respectively, but are 29% lower for TGM/SO2. This suggests that other emissions, primarily mobile sources were likely a significant source of CO and NOx in the observations, but that oil refineries were the primary source of SO2. Four additional events had higher mercury and lower SO2 concentrations and appeared to be influenced by the SERRF waste incinerator in Long Beach. The TGM/CO slope for all pollution events (defined as [CO2]>90% percentile) was 1.2 x 10-7 mol mol-1, which is about a factor of 4 lower than the Hg0/CO slope observed previously in polluted Asian outflow.