Lec. 29: Human Effects: Air Pollution & Heat Islands (Ch 14)

1. Lec. 29: Human Effects: Air Pollution & Heat Islands (Ch 14) • Atmospheric pollutants • Atmospheric controls on air pollution • Urban heat islands http://www3.gov.ab.ca/env/air/index.html

2. Science & air pollution

3. Science & air pollution

4. Science & air pollution

6. In air: by “resolved” wind “Turbulent diffusion” (same as “turbulent dispersion”) is name given to mixing due to the unresolved scales of motion, ie. the turbulent component of the wind

7. 3. Responses/consequences • deposition to soil, plant, ocean, animal…

8. Particulates soot, pollen, etc. and (eg.) asbestos... strongly affect visibility, so most noticeable. Classified by size: eg. PM10 (diameter < 10 m) remains suspended and can enter lungs… PM2.5 (“fine particles”) Sources: natural fires, eruptions, breaking ocean waves, wind-entrained dust** and pollen. Secondary particulates formed by coagulation of gases. Small terminal velocities (slow “gravitational settling”) imply long residence time – precipitation the most effective removal process (aerosols are the CCN at heart of precipitates; and “scavenging” by falling droplets removes other particulates • **soil erosion – dust dislodged by wind stress on surface in combination with bombardment by “saltating” particles in the “saltation layer” above which is the suspension layer • soil condition (moisture, friability) plays a role • leaving stubble strips to shelter the soil – means to reduce wind stress on the soil (wind “pulls on” the straws instead)

9. Human effects – shelter – controlling the environment to mitigate soil erosion

10. Human effects – shelter research observations

11. Human effects – shelter research Lines - computations

12. (This is just to give you a glimpse of what the govering equations look like) Basis of computed winds… • Influence of windbreak is “felt” as a mean momentum sink... U-mtm : horiz.U-mtm.flux vert.U-mtm.flux Windbreak sink  kr U2 … localised by delta-function at x=0, step function at z=H • and as a turbulent kinetic energy sink… eg. in a 2nd-order closure: u2: horiz.flux shear pro. redistr. heuristic

13. iron Zurich; 700 trains/day on line studied “emissions of the railway lines are dominated by ‘iron’ particles, which contribute 67% to the railway related PM10. The ‘iron’ class particles were appointed to the wear of tracks, as well as wheels and breaks of the trains. In addition, ‘aluminium’ and ‘calcium’ particles assigned to abrasion of the gravel bed and re-suspension of mineral dust contribute to the PM10 load: 23% for the ‘aluminium’ and 10% for the ‘calcium’ particles.” (Lorenzo et al., Atmospheric Environment Vol. 40, 2006)

14. Carbon Monoxide (CO) from incomplete combustion of carbon fuels; colourless, odourless, poisonous Sources: fires, eruptions… but taken up by soil micro-organisms so background levels low. Key anthopogenetic source: vehicles

15. Sulphur oxide (SOx ) gases… many natural sources but background levels low. SO2 the key primary sulphur gas, from burning sulphur-bearing fossil fuels. Colourless but smells, can cause respiratory problems. SO3 typically a secondary gas; in moist air forms sulfuric acid  acid rain Fig. 14-3

16. Volatile Organic Compounds (VOC’s or VOx) hydrocarbons, eg. methane (natural). Some carcinogenic. Involved in photo-chemistry of smog • Nitrogen Oxides (NOx) Nitric oxide (NO) non-toxic, colourless, odourless… formed naturally in soil, and this is balanced by natural sinks. Anthropogenic NO associated with combustion, produces secondary NO2 (nitrogen dioxide) … NO2 toxic & corrosive… gives polluted air its yellow/red/brown colour. In moist air reacts to form nitric acid  acid rain • Ozone (O3) secondary pollutant formed when sunlight acts on other pollutants. Smells, irritates. Main ingredient of photochemical smog. Fig. 14-5

17. Anthropogenic pollutant sources in the U.S. (other than vehicles – eg. energy generation from coal, oil, gas…) Fig. 14-1

18. Anthropogenic pollutant sources in the U.S. Fig. 14-1

19. plume dilution • assumes source const. • concentration 1/u Atmospheric controls on air pollution • wind can control or modulate source strength (eg. dust; surface flux of methane off swine lagoons;… • wind is the transport and mixing agent • temperature affects reaction rates; stratification influences the vertical wind, ie. mixing • mixed layer is the short-term sink for pollutants Fig. 14-6

20. elevation of plume means locally no pollution • potential for severe local pollution • high levels intermittently From “Meteorology & Atomic Energy”

21. “Box model” of urban air pollution

22. Contours of mean summer maximum (afternoon) mixing depths h (unit: 100 m) • from Portelli, 1977 • Edmonton, winter, < 300 m

25. Urban heat island 9 pm LST July 4, 1972 (temperature near ground) Fig. 14-9a

26. Maximal late evening and night, and during winter. Causes: • reduced albedo (multiple reflections) • high heat capacity of ashphalt, concrete implies downwelling longwave • precip rapidly drained, dry surfaces low QE results in high QH • anthropogenic heat Fig. 14-9a