Atmospheric Deposition of Air Toxics Matt F. Simcik Division of Environmental and Occupational Health School of Public Health University of Minnesota

Why should we care about Atmospheric Deposition of Air Toxics? from EPA website Atmospheric Deposition is the only source to remote areas such as the National Parks

The Atmospheric System Source(s)TransportDeposition Combustion Volatilization Reaction/Loss Transformation Gas-Particle Partitioning Cloud Scavenging OH Radical Photolysis Wet Dry Particle Gas Particle

Sources Combustion Volatilization Produces both gas and particle phase toxics PCDDs/PCDFs PAHs Produces only gas phase toxics PCBs DDT

Transformations Gas-Particle Partitioning Controls fate of contaminant CgCg CpCp from Simcik 2001 Governed by vapor pressure of toxic and amount of particles in air

Transformations Cloud Scavenging from Simcik 2001

Reaction/Loss Reaction with the OH radical is predominant loss mechanism for most air toxics Most reactions occur fastest in the gas phase Reaction products can be more toxic than parent compounds

Dry Particle Deposition Dry deposition flux = Concentration on particles times deposition velocity. Deposition velocity is a function of particle size Typical value of 0.2 cm/s is often used. from EPA website

Dry Gas Deposition to Terrestrial Surfaces Living plants, soils, and detritus represent a huge amount of surface area available for sorption of gas phase toxics. In particular, waxy, organic surfaces can take up a large amount of lipophilic contaminants. CgCg

Wet Deposition Wet deposition is best done as total deposition (dissolved and particle) from EPA website

Questions that need to be answered What are the current atmospheric loadings of air toxics to the National Parks? How do loadings compare to other areas? What is the historical deposition of air toxics to the National Parks? Are there any adverse effects of atmospheric deposition of air toxics?

Loadings Estimation LoadingDirect MethodIndirect Method Wet Deposition Precip Collector Snow Collection N/A Dry Particle Deposition Surrogate Surfaces Calculation from particle size distribution Dry Gas Deposition N/ACalculation from BCF and Henry’s Law

Air Sampling HI-Vol Air Sampler This provides an operationally defined gas and particle phase Typical 24 hour volumes of 720 m 3

Alternatives to HI-VOL Samplers MethodAdvantageDisadvantage SPMDEasy Passive Concentrations difficult to determine Gas phase only Lichens or other plant material Easy Passive Species differences Concentrations difficult to determine Integrates all deposition processes Surrogate Surface PassiveMust be baby-sat Deposition to surrogate surface Sorption of gases

Historical Deposition Lake sediments have often been used to investigate the historical deposition of toxic contaminants.