Mass Balance Flashcards
What is the purpose of mass balance?
allows us to track the environmental fate of pollutants in a defined compartment
Define steady state
The flow in = flow out of a compartment, i.e. M in a compartment remains constant
What are the characteristics of a long residence time?
- long lifetime
- potential for long-range transport (i.e. move form cities to remote regions)
- efficient mixing (has time to mix)
- global concern
What are characterisitcs of short resident times?
- short lifetime
- deposit near source (local sink)
- local and regional concern
What is flux?
flow per unit area of the surface through which it’s flowing, units of amount per time per area (e.g. g/(s*cm))
What is dry depostion?
- gases or partciles moving directly from the atmosphere to the Earth’s surface
- often consider contaminants on the surface of particles, so need to consider the speed of the particles moving from the air to the surface: deposition velocity
What is wet deposition?
- rain, snow, sleet, hail
- precipitation rates are usually reported in length over time (e.g. mm/hr or cm/yr)
When do we use an up-going curve?
Pollutant introduced: When F(out) will increase until the sinks (i.e. what goes out) equals the input rate
When do we use a down-going curve?
Pollutant emission stopped: F(out) will decrease until it reaches zero
What are 4 examples of first order reactions in the environment?
- decomposition of radio isotypes
- hydrolysis of pesticides in lake
- thermal decomposition of N2O5
- photolysis of NO3 in rivers
When can we assume pseudo first order reactions?
if one or two reactants is in a very large excess, we can combine the constant concentration with the rate constant to get the psuedo first order rate constant
What is half-life?
The time required for [A] to decrease to half of the initial value of [A]0
