Air Quality Exam 2

Boundary layer process

Day time data does not change as much

OO UTC

Daytime boundary layer

How to determine which conditions are present

Density is key Must always compare parcel to its environment

Avogadro's Hypothesis

Equal volumes of all gases, measured at the same T and P, contain the same # of molecules

Types of chemical transformation

Oxidation processes Photodissociation

Atmospheric boundary layer

Part of troposphere Varies in direct response to surface forces Free atmosphere Strong day/ night variation in troposphere

Signs that the atmosphere has been mixed

Pressure, temp, density NOT the same Virtual potential temp IS the same

The Gaussian Plume Model

Provides mathematical method of estimating averages, used for point sources, generally assumes continuous emissions

Oxidation processes

Rate of a chemical reaction (k) depends on: 1. Activation energy 2. Temperature

Emission Factor Rating

Rate quality of emission factor A- excellent B- above average C- average D- below average F- poor

Richardson Number (Ri)

Ratio of stability compared to vertical wind shear. The smaller the number the more turbulent. Laminar flow becomes turbulent when Ri < 0.25

Dispersion is transported by _______________

Wind -many scales of motion in the atmosphere -winds regularly and accurately observed -DOESN'T necessarily reduce the pollutant concentration -can vary dramatically in short distances, especially vertically

SD depends on what

Wind and time of day

Transformation

- Chemical reaction (oxidation) - Photo-discoloration --> sunlight can split molecules - Gas to particle conversion - Solution (can lead to formation of acids)

Dispersion

Advection (transport) and diffusion Includes: -transport -diffusion -transformation -deposition

Components of CAMEO

1. CAMEO: chemical database manager 2. ALOHA: air dispersion model 3. MARPLOT: mapping application

Historical pollution episodes

1. Meuse VALLEY, Belgium. December. Fog, anticyclone, inversions. PM SO2 --> H2SO4 (63 deaths) 2. Donora, PA. October. Polar H over northeast PA. Very light winds in a river valley 3. Chernobyl 4. Kuwaiti Oil Fires

To calculate density you need 2 things

Air Parcel Density Environment

Main parts of boundary layer

A very turbulent mixed layer Residual layer containing less turbulence (left over from previous days mixed layer) Nocturnal boundary layer of sporadic turbulence

Net effect of automobile exhaust?

Absorbed a form of sunlight to create third molecule. Production of ozone, with the presence of hydrocarbons, there will be chemical reactions that take place to cause formation of ozone

Weaknesses of the Box Model

Assumes pollutant mixes uniformly through volume, result is an average concentration

ALOHA

Atmospheric dispersion model for SURFACE releases Designed to produce results quickly for first responders

AERMOD

Based on gaussian plume model Designed to model SHORT RANGE dispersion form stationary industrial sources Primary model used for regulation Strength: the way they represent the sources

Why are air pollution episodes significant

Because they provide solid scientific documentation that exposure to elevated ambient pollutant levels can cause acute illness and even death

Gaussian Distribution

Bell shaped curve, normal curve. Models mimic natural systems well and can therefore be used as a predictive model. Need to know mean, variance, and SD.

Puff

Big emission and then nothing & so on

Wind shear generates vertical motion, but ________ often dampens it

Buoyancy

Atmospheric Dispersion Models

CAMEO and HYSPLIT

Strengths of the Box Model

Can accommodate many sources, ideal for urban air quality analysis

Air pollution illnesses characterized by

Cough Shortness of breath Chest pain Eye and nose irritation

Tv ______ as parcels rise and sink

Changes

Air Pollution Episodes

Characterized by significant short term increases in atmospheric pollutant concentrations above normal daily levels

Urban Air Pollution

Commonly referred to as smog

CAMEO

Computer Aided Management of Emergency Operations Designed to estimate local impact Weather conditions don't vary Gaussian Plume Model

Simplified Gaussian Plume Model tells what

Concentration at point

Properties of Gaussian Plume Model

Concentration proportional to emission rate Concentration diluted by wind Time averaged concentrations have bell- shaped distributions SDs (lateral and vertical) of concentrations - Related to turbulence - Increase with distance from source

Most common plume shape

Conical

HYSPLIT

Designed to estimate LONG RANGE transport and dispersion Uses operational NWP (National Weather Predictions) models as input: computer simulation of atmosphere Gradient transport model Can run forwards and backwards- "where was this weather at yesterday?"

Uses for Virtual Potential Temperature

Determine stability and thus potential for mixing Identifying the depth of the near- surface layer through which pollutants will be mixed

Nonlocal technique using virtual potential temperate (θv)

Displace parcels a small distance upwards AND downward from ALL PARTS of the virtual potential temperature profile

Automobile exhaust

Emits carbon monoxide (CO), carbon dioxide (CO2), hydrocarbons (HC), NO, and NO2

The Box Model

Examines a fixed model of air (like a watershed for the atmosphere)

Subsidence inversions

Formed over large geographical areas as the result of the subsidence of air in high- pressure systems. As air subsides to lower altitudes, it compresses the air beneath it, causing temperatures to rise. Generally between 850- 500mb

Surface forces

Frictional drag Evapotranspiration Heat transfer Terrain Pollutant emissions

Lofting plume

Growing more upwards

Contributing factors to air pollution episodes

Increased industrialization Limited pollution control efforts Population growth

Virtual Potential Temperature (θv)

Is the Tv (K) that a parcel of air would have if you expanded it or compressed it (without adding or removing heat) from its existing pressure to 1000mb. BEST measure of density difference between an air parcel and its environment

Residual layer

Left over layer from yesterday Turbulence decays as thermals dissipate Virtual potential temp. becomes nearly constant with height

Wind rose

Length of petals indicates frequency of wind direction

Moist air is _____ dense than dry air

Less

Which historical pollution episode led to the British Clean Air Act?

London in December. Fog, anticyclone, light winds. Incredibly low visibility with PM and SO2. About 4000+ deaths. Lots of sickness

Cities with a history of smog

Los Angeles, Houston, London

Wind

Mean + eddy

Morons are comparable to _________ because they move in an unpredictable manner

Molecular diffusion

The Gradient Transport Model

Most sophisticated way to measure

Mixed layer (ML) Daytime feature

Near surface layer where pollutants are mixed Turbulence driven by convection produced by warming at surface (solar radiation) and cooling at top of cloud layer (emitted radiation) Turbulence mixes heat, momentum, and moisture so vertical profile is uniform

12 UTC

Nighttime boundary layer

Eddy

Refers to an infinite variety of turbulent motions Responsible for much of the viscosity at scales larger than the molecular Transfer properties "from rich to poor" Transport properties "down the gradient"

Roughness length

Related to how "rough" the surface is DOES NOT mean how tall the obstacle is Greater roughness= greater amount of eddies trees> corn> grass> snow

Deposition

Removal from the air Gravitational setting Impaction/ interaction with surface features Serve as cloud condensation nuclei Scavenging by precipitation

The Gaussian Equations

Requires input of SD (lateral) and SD (vertical) -both are functions of: dispersive nature of atmosphere and distance downwind

Lewis F. Richardson and the Cascade of Energy

Researched eddies motion at larger scale transferred to smaller scales

Plume

Results from a continuously emitted source

Vertical mixing of Air Parcels by Eddies

STABLE conditions RESIST vertical mixing UNSTABLE conditions ENHANCE vertical mixing Neutral conditions don't offer resistance

Factors that contribute to pollution episodes

Slow winds Presence of many sources Warm- core high pressure systems- deep features tend to last long time Subsidence inversions

Coning plume

Spread uniform laterally and vertically

Diffusion

Spreading out of pollutants in all directions by molecular and turbulent motion (random motion of molecules). Reduces concentration of pollution

The average plume

Spreads out like a cone until it hits the ground or a stable layer in the atmosphere Has max pollutant concentration in the center and at the source Becomes more dilute both away from the source and towards the edge of the cone

Atmospheric Stability Classes

Stability classes relate lateral and vertical spreading of a plume to wind speed and solar intensity / cloudiness

Factors that contribute to turbulent flow in a layer

Stability- turbulence favored by unstable or neutral conditions Vertical wind shear- turbulence favored by large vertical wind shear

Turbulent motion can occur with both ______ and ________ conditions

Stable and unstable

Small SD means

Stable conditions

Photodissociation

Sunlight is source of photons

Virtual Temperature (Tv)

The temp that dry air must have in order to have the same density of moist air at the same pressure. Accounts for the effect of water vapor on density by adjusting the air temperature to a warmer value

Drunks are comparable to _____________ because they move in a manner that has some pattern to it

Turbulence

Nocturnal Boundary Layer

Turbulence becomes sporadic Virtual potential temps become weakly stable Oscillatory motions are common (up and down)

Looping plume

Turbulence in boundary layer Good for air quality conditions

Large SD means

Turbulent conditions, increases with distance from the source

Fumigating plume

Unstable beneath plume, stable above

General Gas Law for Dry Air

Warmer air= less dense Colder air= more dense

3D display of Gaussian Plume Model

on x (downwind) and y (lateral, crosswind) plot, z is up and can't ever be negative