Title: Atmospheric Deposition of Air Toxics
1Atmospheric Deposition of Air Toxics
- Matt F. Simcik
- Division of Environmental and Occupational Health
- School of Public Health
- University of Minnesota
2Why should we care about Atmospheric Deposition
of Air Toxics?
Atmospheric Deposition is the only source to
remote areas such as the National Parks
from EPA website
3The Atmospheric System
Source(s)
Transport
Deposition
Transformation
Wet
Combustion
Volatilization
Gas
Gas-Particle Partitioning
Particle
Dry
Cloud Scavenging
Gas
Reaction/Loss
Particle
OH Radical
Photolysis
4Sources
Combustion
Produces both gas and particle phase toxics
PCDDs/PCDFs
PAHs
Volatilization
Produces only gas phase toxics
DDT
PCBs
5Transformations
Gas-Particle Partitioning
Cg
Cp
Controls fate of contaminant
Governed by vapor pressure of toxic and amount
of particles in air
from Simcik 2001
6Transformations
Cloud Scavenging
from Simcik 2001
7Reaction/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
8Dry Particle Deposition
from EPA website
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.
9Dry Gas Deposition to Terrestrial Surfaces
Cg
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.
10Wet Deposition
from EPA website
Wet deposition is best done as total deposition
(dissolved and particle)
11Questions 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?
12Loadings Estimation
Loading Direct Method Indirect Method
Wet Deposition Precip Collector Snow Collection N/A
Dry Particle Deposition Surrogate Surfaces Calculation from particle size distribution
Dry Gas Deposition N/A Calculation from BCF and Henrys Law
13Air Sampling
HI-Vol Air Sampler
This provides an operationally defined gas and
particle phase
Typical 24 hour volumes of 720 m3
14Alternatives to HI-VOL Samplers
Method Advantage Disadvantage
SPMD Easy 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 Passive Must be baby-sat Deposition to surrogate surface Sorption of gases
15Historical Deposition
Lake sediments have often been used to
investigate the historical deposition of toxic
contaminants.