6.3 Photochemical smog Flashcards
source of tropospheric ozone
the reaction of nitrogen oxides (NOₓ) and volatile organic compounds (VOCs) in the presence of sunlight. These precursor gases mainly come from vehicle emissions, industrial processes, and burning of fossil fuels. Ozone forms as a secondary pollutant during these reactions in the lower atmosphere.
what is tropospheric ozone
in the troposphere, ozone is considered a pollutant
the effects of tropospheric ozone
- ozone is a toxic gas and an oxidising agent
- it damages crops and forests
- irritates eyes
- can cause breathing difficulties
- ground level ozone reduces plant photosynthesis and can therefore reduce crop yields significantly
- highly reactive and can attack fabrics and rubber materials
how are secondary pollutants formed?
in the presence of sunlight, when primary pollutants undergo a variety of reactions with other chemicals already present in the atmosphere. tropospheric ozone is an example of a secondary pollutant.
how many primary + secondary pollutants are found in photochemical smog
100
why is tropospheric/ground-level ozone a secondary pollutant
bc it is formed by reactions involving oxides of nitrogen (NOx)
why does ozone drift to surrounding areas
because it can take a number of hours, hence the polluted air may have drifted into suburban+ surrounding areas
thermal inversions
trap smog in valleys + basins i.e. LA, Santiago, Mexico City, Rio de Janero
the air is unable to disperse bc cold air that is trapped beneath a layer of less dense, warm air from the surrounding mountains and hills prevents the warm air from rising
cold air is denser than warm air, so it traps the warm air below and causes concentrations of air pollutants to build up near the ground instead of being dissipated by ‘normal’ air movements.
what about urban areas?
urban microclimates generally have less vegetation than surrounding rural areas, and the concentration of buildings, industries and offices generates much heat.
how does deforestation or burning produce smog? case study
forest fires of Southeast Asia in the late 1990s and in 2012-2014 produced the Asian ‘brow haze’, throughout much of Malaysia, Indonesia and Singapore
why are places with high air pressure more prone to smog?
winds in high pressure systems are usually weak meaning pollutants remain in the area and are not dispersed
poor air quality -> persists for few days bc stable high pressure conditions generally prevail
notably Mediterranean climates have conditions of high air pressure all season, meaning poor air quality can remain for months
elements of areas prone to smog
local topography - low lying areas
climate - high air pressure areas
population density - number of vehicles
economic losses caused by urban air pollution
- cost of clean up strategies
- loss of tourism
- decreased worker productivity
- increased cost of health care
- decreased crop productivity
- cost of replacing materials
case study economic losses caused by urban air pollution
world bank indicates that the cost of air pollution in China is worth approx. 4% of its GDP anually
pollution management strategies in which photochemical smog can be managed
clean up:
- reforistation
- re-greening
reduce the amount of pollutants released into the environment:
- fitting cars with catalytic convertors to reduce NOx emissions
- increased use of public transport -> reduces total emmissions of fossil fuels
- preventing cars in parts of the city (green zone in FFM) /legislation
changing human activity:
- wearing masks to help reduce inhalation of pollutants
