GEOB 402
key points from Hemispheric transfer reading
under current conditions, local and regional emission changes have the greatest impact on surface air quality For fine particles, the impact of intercontinental transport on surface air quality is primarily episodic a 20 per cent decrease in anthropogenic emissions of nitrogen oxides in any three of these regions together would achieve a 30 to 70 per cent reduction in annual mean O3 concentrations
impacts of air pollutant deposition on ecosystems
water and soil acidification, lake eutrophication, and both fertilization and damage to agro- and forest ecosystems
the entrainment zone
Air bubbles rise through convection into the PBL causing spikes in thermal energy
"arrowhead" diagram
Predicted annual maximum converging with minimum as averaging time increases
primary vs. secondary pollutants
Primary: substances emitted directly from sources (e.g. methane, sulphur dioxide) Secondary: pollutants that arise from chemical reactions with primary pollutants often acting as precursors
dust impacts on climate change and weather
Radiative forcings/aerosol relationship -- absorb radiation and directly warm atmosphere Act as CCN for precipitation
synoptic meteorolgy
a two-stage process involving determination of a relatively small set of atmospheric circulation types (maps) and the assessment of weather elements in relation to these types -Modulates transport and dispersion on timescale of days and greater -Dictates the extent to which ventilation and deposition processes occur -Affects boundary layer depth -Temperature and radiation conditions that promote chemistry -Can affect emissions -Dictates the lengths of 'episodes', seasonal differences
mesoscale
fronts, hurricanes, squall lines, slope flows, land/sea breezes, thunderstorms -When the earth's rotation doesn't impact events
dry deposition
gases and particles are transported by turbulent mixing to surfaces
importance of mesoscale
-A high proportion of the world's population live in coastal zones and/or where the terrain is complex -essential to the assessment and modelling of air pollution dispersion in such regions -Often the phenomena concerned are diurnally repeatable and geographically fixed* -creates hope for successful modelling
McKendry article on synoptic climatology and ozone concentrations in LFV
-Summertime daily maximum ozone concentrations appear to be strongly modulated by the synoptic-scale atmospheric circulation -Synoptic scale conditions that produce clear skies, warm air, light winds reduce the mixing depth and promote reduced air quality
ways of managing air pollution (Oke et al)
-targeting the emission processes, e.g. by requiring proper technological measures, such as emission control systems -fuel switches -efficient use of resources -enforcing a temporary or indefinite ban of vehicles and motors
Chernobyl
1986 90X Hiroshima Nuclear plant explosion in Russia Radionucleides deposited in Lower Fraser valley midlatitudes /Jet Stream carried these around the planet several times
Fukushima
2011 Travelled into Pacifica, looped to Hong Kong and circled back across Asia Rapidly transported to West Coast of North America about 6-8 days later Significant effects on groundwater
Canada-wide standard for PM2.5
30 micrograms/m3 24-hour averaging time
Canada-wide Standard for ozone
63 ppb 8-hour averaging time
Gaussian plume model
A plume emerges from an elevated point source (a stack) that is continuously emitting pollutants at a constant rate As the pollutants enter the urban atmosphere, they form a plume that is advected by the mean wind and mixed by turbulence, which regulates its spread mean pollutant concentration is greatest in the central core and diminishes toward the edges → bell-shaped distribution
diffusion vs. dispersion
Diffusion: the process in which a constituent moves through a concentration gradient (molecular diffusion) Dispersion: the mixing due to physical process (often gets called "diffusion")
mechanically-forced circulation
Driven purely by the terrain itself (not its heating/cooling)
tragedy of the commons
Global atmospheric commons Injection of air pollutants in quantities such that the global atmosphere is changing with negative impacts on humans
dust impacts on biomass productivity
Iron fertilization for plant growth Reaches ocean by long-range dust transport Simulative productivity -- dust Unknown consequences
planetary boundary layer
Layer of the troposphere that is directly influenced by the presence of the Earth's surface -Responds to surface forcings with a timescale of >1 hour -0-3 km deep
scales of air pollution
Local: 5km Urban: 50km Regional: 50-500km -- downwind urban problems, slow reacting primary pollutants (e.g. acid rain), visibility Continental: 500-1000s km -- transboundary issues Global: intercontinental transport, CFCs, radionucleides
diurnal variation in the PBL
Lots of convection in the afternoon (summertime) Stable nocturnal boundary layer due to cooling of the surface
thermally-forced circulation
Sea-breeze -Uplift at boundary -Cools down quickly at night Mountains/valleys Urban effects
Froude number
The ratio of the natural wavelength of the air to the wavelength of the mountain barrier Fr = V/ Nx N= Brunt-Vaisala frequency (stability factor) x= width of mountain V= wind speed
AOT40
accumulated excess of hourly ozone concentrations above 40 ppb during a relevant growing season
averaging time
averaging out the dispersion of instantaneous particles over a certain amount of time
SUM06
comprised of the 90-day maximum sum of the 0800 through 1959 hourly concentrations of ozone > 60 ppb
ventilation coefficient
depth/height [at which it can mix] + wind speed Combo of depth and wind speed How much potential there is for dilution
Siberian fire plume
intense wildfire plume from Siberia that affected the air quality across the Pacific Northwest on July 6-10, 2012 Stable atmospheric conditions along the coast limited the initial entrainment of the plume and caused local anthropogenic emissions to build up Overall, the smoke plume contributed significantly to the exceedances in O3 and PM2.5 air quality standards and objectives that occurred at several communities in the region during the event
plant effects from ozone
leaf stippling, pinish hue, spotting, premature senescence, when the stomata are open and taking in pollutants
chemical weather
local, regional and global distributions of important trace gases and aerosols and their variabilities on time scales of minutes, to hours, to days On a day to day basis, we see variations in chemistry like we do in humidity, temperature, etc
plume shapes
looping coning fanning lofting fumigation
transport
movement by wind (concentration may not change)
macroscale
standing waves, tidal waves, baroclinic waves
baseline concentration
the concentration of a given species in a pristine air mass in which anthropogenic impurities of a relatively short lifetime are not present
combustion
the sum of chemical reactions between hydrocarbons and atmospheric oxygen (O2) that produce heat and light, and release carbon dioxide (CO2) and water vapour into the atmosphere
fugitive emissions
the unintended 'escape' of gases held in pressurised containers
urban canopy layer
the zone of human occupation and the quality of the air at this level is critical for assessing the public health consequences of air pollution
microscale
tornadoes, dust devils, thermals, plumes, turbulence