7.2 photochemical smog, 7.3 thermal inversion

types of smog

industrial and photochemical

industrial smog

common in humid cities with high dependency on coal; results from primary pollutants

photochemical smog

common in urban centers with calm wind and warm/sunny weathers; results from secondary pollutants

precursors (NO2)

broken by sunlight into NO + O (free O + O2 > O3)

Precursors (VOCs)

VOCS (hydrocarbons) that bind with NO and form photochemical oxidants

Precursors (O3)

forms when NO2 is broken by sunlight and free O binds to O2

sunlight conditions

drives O3 formation by breaking down NO2 > NO + O; then free O atom bind with O2

warmth conditions

hotter atm. temp. speeds O3 formation, evaporation of VOCs and thus smog formation

Normal O3 formation

1) morning commute leads to higher NO2 levels from car exhaust

2) sunlight breaks NO2 into NO + O

3) O bonds with O2 to form O3

4) O3 formation typically peaks in afternoon when sunlight is most direct and NO2 emissions from morning traffic have peaked

5) At night, O3 reacts with NO to form NO2 and O2 once again; O3 levels drop overnight

photochemical smog formation

1) sunlight breaks NO2 into NO + O

2) O bonds with O2 to form O3

3) VICs bond with NO to form photochemical oxidants

4) without NO to react with, O3 builds up instead of returning to O2 and NO2 overnight

5) O3 combines with photochem. oxidants (NO + VOCs) to form photochemical smog

Factors that increase smog form

More sunlight = O3; warmer temp., speeds evap. of VOCs and rxn that lead to O3; higher VOCs emissions, inc. vehicle traffic, inc. NO2 emissions and therefore O3 formation, more traffic > more NO2, hotter temps due to low albedo of blacktop; more VOCs due to gas stations and factories

environmental impacts

reduces sunlight; limiting photosynthesis; O3 damages plant stomata and irritates animal resp. tracts

human impacts

resp. irritant; worsens asthma, bronchitis; COPD; irritates eyes

economic impacts

inc. health care costs to treat asthma, bronchitis, COPD; lost productivity due to sick workers calling out; dec. ag. yields due to less sunlight reaching crops and damage to plant stomata

vehicles reduction

dec. the number of vehicles on road dec. NO2 emissions; fewer vehicles = less gas = fewer VOCs

energy reduction

inc. electricity production from renewable sources that don’t emit NOx (solar, wind, hydro); nat. gas power plants release far less NOx than coal

urban heat island effect

urban areas tend to have higher surface and air temperature than surrounding suburban and rural areas due to low albedo and less evapotranspiration

thermal inversion

cold air trapped at surface of earth beneath the warner mas above, so pollutants are trapped

effects of thermal inversion

resp. irr., dec. tourism revenue, dec. photosynthetic rate