Air pollutants in the troposphere Basics: Chemical fate of pollutants in the troposphere Photochemical smog and ‘classical smog’ The Gothenburg protocol Norwegian emissions Air Quality Guidelines and exceedances in Norway Heavy metals POPs
Tropospheric chemistry in a nutshell O2 H2O The ‘detergent’ of the atmosphere hn l<310nm O3 O* OH. (hydroxyl radical) hn M NO CO M O2 O(3P) O2 CO2 hn NO2 hn NO NO2 H. NO NO2 sink: OH, M O2 H2O2 (hydrogen peroxide) O2 HNO3 HO2 . HO2 . (hydroperoxyl radical) Wet deposition Dry deposition
Oxidation of methane and otherhydrocarbons O2 H2O hn l<310nm O3 O* OH. (hydroxyl radical) hn M NO CH4 O(3P) O2 O2, M H2O hn NO2 hn NO NO2 CH3. NO NO2 sink: OH, M O2 H2O2 (hydrogen peroxide) O2 HNO3 HO2 . CH3O2 . (methylperoxyl radical) Wet deposition Dry deposition
NO NO2 CH3O2 . (methylperoxyl radical) CH3O . O2 HO2 HCHO (formaldehyde) CH3O . Further degradation and oxidation of formaldehyde via photolysis or reaction with OH or HO2 to CO and finally to CO2
Photochemical smogLos Angeles Smog • Where there is much traffic and sunshine • Main reagents: • NOx, VOC,O3, CO • Oxidative Huston, Texas
Fluctuations in concentrations of photochemical smog during the day and PAN Sunlight • Sunlight+ VOC + NOx = O3 O3 The dominant oxidant is O3. The figure is a generalisation based on various studies.
When exposed to sunlight, NO2 can cause formation of ozone: First atomic oxygen is formed Atomic oxygen can react with O2 to form ozone Since mainly NO is emitted, we need a reaction that gives NO2. However, oxidation by O3 would reverse the reaction, i.e. decrease O3 Reactions with free peroxyl radicals may instead oxidise NO to NO2 RO2• radicals may have been formed through reactions involving hydrocarbons, e.g.: A chain reaction involving CO, OH• and HO2• may also produce NO2 (net reaction): NO2 + hν (λ< 400 nm) NO + O O + O2 + M O3 + M*NO2 + O2 O3 + NO O3 + NO NO2 + O2(O3 is often low within cities) NO + HO2• NO2 + HO• NO + RO2• NO2 + RO• OH• + CH4CH3• + H2O CH3• + O2 + M CH3O2• + M* CO + NO + O2 CO2 + NO2 Why is the oxidant concentration in photochemical smog (mainly ozone) increasing during mid-day?
The non-linearity between NOx and VOC O3 concentration isolines Both NOx and VOC emissions must be reduced 160 ppb VOC conc. 140 ppb 120 ppb 100 ppb At high NOx levels: NO is titrating O3 → O3 may increase if only NOx is reduced. NOx conc.
Classic smogLondon smog • Where there is much burning of fossil fuels • Main constituents: • Particles (incl soot), CO, S-compounds
Local S-limits for residual oil Catalytic cars Limits for point sources Focus on NO2 and PM Regional LRTAP Geneva 1979 SO2 NOx VOC Multi Gothenburg 1999 Climate Change IPCC Rio Kyoto 1997 Kyoto approved by China 2002 Marrakesh Priorities given to local, regional and global pollution problems LRTAP: Long-range transboundary pollution IPCC: Intergovernmental Panel on Climate Change
The Gothenburg protocol (1999) A sophisticated environmental agreement • Addresses three different air pollution problems: - Acidification - Eutrophication - Ground-level ozone • Four different gases/groups of gases: - Sulphur dioxide (SO2) - Nitrogen oxides (NOx) - Ammonia (NH3) - Volatile organic compounds (NMVOCs) • Based on scientific studies through an integrated assessment of critical loads, deposition patterns and abatement costs
Commitment reached Norwegian SO2 emissions
Historical development of sulphur dioxide emissions in Europe (Source: Vestreng et al., 2007)
European sulphur emissions 1980-2000 • The decrease is generally larger after 1990 • Greater from sources that emit S that is deposited in sensitive regions 1000 tones/yr
European nitrogen emissions 1980-2000 Regional differences in N emission changes are more pronounced than for sulphur emissions. 1000 tones/yr
Norwegian emissions of particles (PM10) • Particles less than 10 μm are along with CO and NOx of largest importance for air quality in cities • Burning of biomass and metallurgic industry the most important sources
Classical air pollutants are generally reduced in Europe Figure from Monks et al 2009
Norwegian emissions of environmental toxins • Large reductions due to • Improved flue cleaning technology • Esp. waste incineration • Shutdown of chemical and metallurgic industry • Pb reduction due to unleaded petrol
Air quality guidelines for some pollutants (mg/m3) HEALTH VEGETATION • Concentration of air pollutant below which adverse effects to human health are acceptable. a. WHO argue that if the 24 hour limit is satisfied, the annual average will be satisfactory. Guideline for 10 min: 0.5 mg/m3
Concentrations in Oslo (down town) air. Guidelines NOx PM10
Developed vs developing countries Monks et al 2009
Average annual PM10 concentrations (particular matter with diameter less than 10 μm) in selected Asian cities in 2003 WHO guideline
Air pollution – not only local and regional problem anymore Increasing evidence that many air pollutants are transported on a hemispheric or global scale. Observations and model predictions show the potential for intercontinental transport of • ozone and its precursors • fine particles • acidifying substances • mercury • persistent organic pollutants
Ozone (surface level) – damage to crops Exposure-response functions for yield loss
Persistent Organic Pollutants (POPs) • The grasshopper effect”: POPs evaporate and deposit several times(distillation) • Concentrations in cold polar areas may therefore become serious.
POPs (Europe)Trends of PCDD and PCDF DIOXINS and FURANS PCDD: Polychlorinated dibenzo-p-dioxins PCDF: Polychlorinated dibenzofurans C, Cl, O, H 2,3,7,8-tetrachlorodibenzodioxin concentrations in air and soil emissions