Week 5.docx

Air Quality and Climate Change – Mitigation Measures Week 5 1. Impact of air quality on climate change Greenhouse Gases (or contribute to warming) Air Quality Pollutants O3 – Ozone NOx – Nitrogen Oxide CH4 – Methane SO2 – Sulphur Dioxide CO2 – Carbon Dioxide NH3 – Ammonia N2O – Nitrous...

Air Quality and Climate Change – Mitigation Measures Week 5 1. Impact of air quality on climate change Greenhouse Gases (or contribute to warming) Air Quality Pollutants O3 – Ozone NOx – Nitrogen Oxide CH4 – Methane SO2 – Sulphur Dioxide CO2 – Carbon Dioxide NH3 – Ammonia N2O – Nitrous Oxide BC – Black Carbon IVOC – Intermediate volatile organic compounds IVOC – Intermediate volatile organic compounds SVOC – Semi volatile organic compounds (can be in gas or aerosol phase) SVOC - Semi volatile organic compounds (can be in gas or aerosol phase) BC – Black Carbon O3 – Ozone Air Pollution refers to the presence of substances in the atmosphere that have a detrimental effect on humans and other living organisms. Greenhouse Gases are gases that have the ability to absorb and trap heat. Air quality – can be precursors to pollutants with negative or positive radiative forcing. NOx, SO2, NH3, VOC Are all precursors of secondary aerosol p They reflect solar radiation back to space which has a cooling affect Aerosols have a negative (cooling) radiative forcing on climate Reductions in precursors of secondary aerosol likely to lead to increase in temperature Black Carbon (BC) A product of incomplete combustion in UK emitted from diesel vehicles Black Smoke (AQ) or soot Can be a substantial part of PM2.5 Absorbs solar radiation positive (warming) radiative forcing e.g. Emissions of Black Smoke from Portugal (2003) Over a dark surface such as an ocean or forest, the forcing can be negative Over a bright surface such as a desert or snow or above cloud, the forcing is positive Forcing is therefore dependent upon the direction of the wind blowing the smoke (in this example) Tropospheric O3 Secondary pollutant One of the largest single components of the current radiative forcing of climate NOx, VOC and CO are precursors of ozone (O3) NO2 emissions need to be controlled (as well as VOC) AQ management is concerned with ground-level ozone Radiative forcing of climate is more influenced by ozone at higher altitudes NO2 in presence of sunlight and oxygen causes formation of ozone Greenhouse Gases (GHG) Most effective high in the troposphere The radiative impact is high and temperatures are low Aerosol Effect also depends on altitude Air pollutants Concentrations at the surface is most important issue in AQ Distribution is highly inhomogeneous and most are short-lived Global Warming Potentials (GWP) and Radiative Forcing metrics to describe AQ pollutants such as aerosols on CC is problematic! Also – ozone cannot be assigned a GWP because it is secondary. The relationship between the effects on regional radiation of pollutants and regional temperature response is far from clear, especially for pollutants that are not evenly distributed. In principle, any pollutant that contributes to both local and regional pollution problems and also acts as a radiative forcing agent or changes the distributions of radiative forcing agents, may potentially produce a link between AQ and CC issues 2. Impact of climate change on air quality Increasing Temperatures Will lead to changes in chemistry associated with ozone formation Will lead to increase in water vapour in the atmosphere - ↓ background O3 - ↑ urban O3 where NOx is high Potential increase in flux of O3 from stratosphere to troposphere from NO and NO2 NO2 in presence of sun creates ozone CO, CH4 and NMVOCs are also emitted Ozone can be deposited Ozone in presence of water creates OH – this can react with the start of the cycle Ozone isopleths Should NOx or VOC be decreased as a way to decrease ozone e.g. Heatwaves 2003 Correlation between heat and sunlight– effects ozone chemistry Heat waves are predicted to be ‘typical’ by the 2040s And will lead to ↑ summer pollution events With heatwaves and increasing temperatures massive increase in Biogenic VOCs are seen: BVOCs are oxidised by OH/ozone/NO3 and Nox and produce ozone and secondary organic aerosol High frequency of summer pollution events Increases in emissions of biogenic compounds e.g. Isoprene Trees: Emissions of BVOC are different for different tree species Tree planting schemes aimed at energy production or carbon sequestration should take into account the potential for increased emissions of VOC and their impact on ozone and SOA Hot/dry summers ↓ the uptake of O3 through the stomata of plants which leads to ↓ damage to plant but ↑ in ground level O3 Winter smog events likely to be less prevalent because of ↓ winter stagnation events 3. Mitigation measures for air pollution and climate change Difficult to use output from current climate models to investigate the effects of climate change on regional AQ Improvements in the temporal resolution are needed to examine processes with daily variations, and seasonal changes in emissions from natural sources Shorter timescales are also needed for projections (2020 – 2030, for example). Surface T and soil dryness are key to understanding the likely severity of future summer pollution episodes Climate models are becoming more sophisticated, but still need improvement to represent the real world Simplest chemistry models only include chemistry for NOx, O3, CH4 and CO – a total of 20 species Complex chemistry models simulating urban pollution may need to treat over 100 species Global tropospheric-climate modelling typically include 50-60 species including isoprene and their oxidation products NO model can represent all the important chemicals found in the atmosphere e.g. Master Chemical Mechanism (MCM) http://chmlin9.leeds.ac.uk/MCMv3.3.1/home.htt Near explicit mechanism Describes the degradation of 142 NMVOC emitted in the atmosphere All molecules react with NO3, O3 and OH Over the past 20-30 years most attention has been focused on mitigation of AQ impacts through: (1) legislation - LEZs (2) changes to technology – electric cars Little or no consideration has been given to the impacts (beneficial or detrimental) on climate Extra emissions need to be considered (air quality and climate change need to work together) AQ policies and CC policies have (largely) been developed separately from one another Mitigation measures can be broadly identified and categorised into: Conservation: reducing the use of resources through energy conservation Efficiency: reducing use and emissions of AQ & climate active pollutants Abatement: the application of a technological approach to reduce emissions Fuel switching: substituting a higher emission fuel with a lower emission fuel Demand management: implementing policies/measures to control or influence the demand for a product or service (conserving energy) Behavioural change: changing habits of individuals to reduce emissions From 2002 to 2020 UK emissions have shown significant reductions: NOx 45% SO2 64% VOC 26% PM10 19% NH3 10% CO2 4% < carbon dioxide hasn’t decreased as much as you’d expect and this is an example of where AQ policy hasn’t aligned with CC policy There have been massive decreases in emissions Reductions observed because the large emitters have now been controlled – mitigation measures! Trade offs: Reduced sulphur in fuel Reduction in SO2 emissions and S limits in fuel Increased (<5%) refinery CO2 emissions These could be offset by improvements to petrol engine efficiencies Flue gas desulfurisation (FGD) Reduction in SO2 emissions Formation of CO2 (~3%) via use of limestone in wet scrubbing Diesel fuel vs Petrol Diesel fuel is generally considered to have GHG benefits over petrol Diesel cars have larger engines than equivalent petrol engines – reduces CO2 benefits Diesel fuel demand is larger so refinery processes used – reduces CO2 benefits Diesel leads to BC (soot) emissions – contribution to warming effects? Selective catalytic reduction (SCR) – put on cars to reduce NOx emissions reduces NOx and CO2 emissions but can increase N2O enables engines to operate with higher efficiencies Mitigations measures that could reduce emissions of AQ and climate-active pollutants Could lead to increased N2O emissions GWP, radiative efficiencies and lifetimes are large Win/wins: Energy conservation measures Benefits of improved efficiencies can be reduced through encouraging increased demand in same (or other) products Combined heat and power Fuel switching to lower carbon or renewables (e.g. coal to natural gas) Reduction in CO2, SO2 and NOx, especially when used with abatement Measure Effect Power generation Fuel switching to lower carbon or renewables (e.g. coal to natural gas) Reduction in CO2, SO2, NOx (esp., if with abatement) Combined heat and power Reduction in AQ and climate-active pollutants if used to replace conventional electricity generation Transport Use of certain new technologies and fuels (e.g. hybrid vehicles) Reduces point of use and fuel chain emissions of CO2 and AQ pollutants Low emission zones Only if newer (more efficient) vehicles replace older (less efficient) vehicles Efficiency Improvements More efficient domestic appliances/industrial processes; improvements in technology Often a proportionate reduction in climate-active and AQ pollutants; benefits of improved efficiencies can be reduced through encouraging increased demand in same (or other) products Demand Management Road user charging Conservation Home insulation Mitigation measures that could reduce emissions of AQ and climate- active pollutants: Climate mitigations measures that could increase emissions of AQ pollutants Measure Effect Increased aircraft fuel efficiency Reduction in CO2 but increase in NOx Fuel-switching (transport) Increased use of diesel in place of petrol (increase NOx and PM) Use of biofuels under certain conditions General Use of N-based fertilisers could ↑ NH3 emissions. N2O emissions may ↑ for some fuels Transport fuels Increased emissions at point of use and increased production emissions of AQ pollutants Domestic use If used in place of electricity of natural gas – could ↑ PM emissions Waste Management Incineration instead of landfill. Reduced CH4 but increases AQ pollutants Forests as a sink for carbon Potential to ↑ emissions of BVOC AQ mitigations measures that could increase emissions of Climate-active pollutants Measure Effect Power generation Flue gas delusulfurisation (FGD) Formation of CO2 through wet scrubbing Transport Abatement of AQ emissions SCR potential to increase N2O Reduced sulfur in fuels Increased refinery CO2 emissions. Measures that could result in increased AQ and Climate-active pollutant emissions Measure Effect Increased demand for products / services Aircraft – increased fuel efficiency has been exceeded by increased demand Transport modal shifts Increased use of short-haul flights at the expense of rail Increased use of coal for electricity generation If used in place of renewables, nuclear or natural gas Use of biofuels under certain circumstances Significant increase in N2O if nitrogen-based fertilisers used; transportation emissions over long distances (if imported); increased AQ emissions if used in high proportions at point of use; fuel-chain emissions increase particularly if significant use of fossil fuels