The study analysed how policies addressing air pollution and climate change interact. A focus was on how measures in one policy area affect emissions and environmental impacts related to the other policy area and quantified ancillary benefits.
The study predicted the effects of three scenarios of cost-effective pollutant reduction:
- A scenario driven by concern for climate impacts
- A scenario targeting the effects on ground level ozone
- A scenario targeting the impacts of suspended particulate matter (PM)
Scenarios were applied to the EU, USA and China and covered a range of pollutants: primary emissions of PM2.5, sulfur dioxide, nitrogen oxides, methane, VOC and carbon monoxide. In all scenarios the starting point for the pollution reductions was the level of emissions achieved through current legislation. For Europe this largely implies the application of existing EU and national legislation on stationary and mobile sources. Reductions were attained mainly by end-of-pipe measures, such as catalytic converters and other cleaning technologies, and retro-fitted measures, such as replacing household stoves. Fuel switching, for example, from oil to gas, was not considered.
The results indicated that the cost-effective reductions in the climate-focused scenario were similar to the air quality-focused scenarios for certain pollutants such as PM2.5, VOC, carbon monoxide and methane. For example, in the EU an additional €25 billion per year expenditure would reduce VOC by approximately 1.5 million tonnes for both the climate-focused scenario and the ozone-focused scenario. The same expenditure would reduce primary PM2.5 by about 300,000 tonnes for the climate-focused scenario and the PM focused-scenario. The response curves are similar to those of Europe and the USA as well as in China. It is noticeable that costs per tonne reduced are generally lower in these regions, and in particular in China.
At all levels of expenditure the climate-focused scenario has only a minor importance for sulfur dioxide and low reductions for nitrogen oxides, due to their small or negative (cooling) impact on the climate. The ozone-focused scenario produced large reductions in nitrogen oxides and the PM-focused scenario produced large reductions in nitrogen oxides and sulfur dioxide.
The results suggest potential co-benefits in integrating climate change policy and air quality legislation for certain pollutants in all studied regions, as reductions may be generating large net benefits from both perspectives. Potentially this could also increase the political acceptance of reductions and allow more ambitious environmental targets to be set. The form of such 'integrated policy' has several options, for example, formally recognising pollutants as climate change agents and involving them in emissions trading schemes. The study also indicates the potential for international co-operation throughout the northern hemisphere on air quality issues, as this would also help mitigate global climate change.