Polycyclic Aromatic Hydrocarbons in the Snowpack and Surface Water in Blackwood Canyon, Lake Tahoe, CA, as Related to Snowmobile Activity

Snowpack in alpine environments may contain appreciable levels of regional pollution acquired through natural processes of wet and dry deposition, as well as from immediate sources such as snowmobile engine exhaust. Understanding the fate and transport of pollutants in alpine environments is a crucial step towards managing emission sources in alpine terrain to mitigate their impacts on natural resources. This study presents detailed chemical analysis for 94 species of polycyclic aromatic hydrocarbons (PAH) in 55 samples of snow and surface water collected in Blackwood Canyon, a tributary to the west shore of Lake Tahoe that is a popular winter recreation area for snowmobile riders. Analyses included toxic and persistent PAH, emitted as products of incomplete combustion and useful for identifying fossil fuel combustion emissions in the environment. Average background snow PAH concentrations were used to estimate background PAH surface loading (μg.m−2). Loadings in excess of the estimated background are mapped and compared with observations of snowmobile activity to determine effects of snowmobile emissions on snow water quality. Loading of heavy PAH, those having three or more aromatic rings, in snow was found to be significantly greater than background loading (α = 5%) where snowmobile tracks cover more than 50% of the snow surface. Loadings were 8–20 times greater than background levels where snowmobile traffic was most concentrated over snow covered roads. PAH were also measured in snow melt and surface water samples in Blackwood Canyon for comparison with snow samples. Flux of PAH (g.day−1) from Blackwood Creek into Lake Tahoe was calculated and compared to estimates of background flux, increasing from 74 g.day−1 to 480 g.day−1 over an 8-day period during spring run-off.