title: Atmospheric deposition of particles at a sensitive alpine lake: Size-segregated daily and annual fluxes from passive sampling techniques.
abstract: Lake Tahoe, a North American alpine lake long appreciated for its clear water and geographic setting, has experienced a trend of declining water clarity due to increasing nutrient and particle inputs. Contributions from atmospheric deposition of particulate matter (PM) could be important, yet they are inadequately quantified. This study established a yearlong deposition monitoring network in the northern Lake Tahoe Basin. Dry deposition was quantified on surrogate surfaces while wet deposition was based on particles suspended in precipitation at 24-hour resolution. The particle size ranges by these passive techniques were 1-64μm and 0.5-20μm in diameter for dry and wet deposition, respectively. Dry deposition of submicrometer (0.5-1μm) particles was also estimated by extrapolation of a lognormal size distribution. Higher daily number deposition fluxes (NDFdryand NDFwet) were found at a near-shore site, confirming substantial impacts of commercial and tourist activities. The two more isolated sites indicated a uniform regional background. On average, daily NDFdryis about one order of magnitude lower than daily NDFwet. Dry deposition velocities increased rapidly with particle size, as evidenced by collocated measurements of NDFdryand ambient particle number concentrations, though it seems less so for wet deposition due to different scavenging mechanisms. Despite fewer "wet" days than "dry" days during the monitoring period, wet processes dominated seasonal particle deposition, particularly in winter and spring when most precipitation occurred. Adopting sediment (insoluble, inorganic) particle fraction estimates from the literature, this study reports an annual particle flux of 2.9-5.2×1010#m-2yr-1for sediment particles with 1-20μm diameter and 6.1-11×1010#m-2yr-1for those with 0.5-20μm diameter. Implications of these findings to the current knowledge of atmospheric deposition in the Lake Tahoe Total Maximum Daily Load (TMDL) are discussed.
authors.affiliation: Division of Atmospheric Sciences, Desert Research Institute, Reno, NV 89512, USA.
authors.forename: Anna Y-C
authors.initials: AY
authors.lastname: Tai
authors.affiliation: Department of Environmental and Occupational Health, University of Nevada, Las Vegas, NV 89154, USA. Electronic address: antony.chen@unlv.edu.
authors.forename: L-W Antony
authors.initials: LA
authors.lastname: Chen
authors.affiliation: Division of Atmospheric Sciences, Desert Research Institute, Reno, NV 89512, USA.
authors.forename: Xiaoliang
authors.initials: X
authors.lastname: Wang
authors.affiliation: Division of Atmospheric Sciences, Desert Research Institute, Reno, NV 89512, USA.
authors.forename: Judith C
authors.initials: JC
authors.lastname: Chow
authors.affiliation: Division of Atmospheric Sciences, Desert Research Institute, Reno, NV 89512, USA.
authors.forename: John G
authors.initials: JG
authors.lastname: Watson
keywords: Dry deposition; Image analysis; Scanning electron microscopy; Surrogate surface; Total maximum daily load; Wet deposition