Local and Regional Air Pollution
This external costs category includes pollutants emissions with impact pathways on a local or regional scale. The most analysed impact pathways are usually those with the major health concerns. Also air pollution impacts on agriculture and on building materials have been studied, but they seem to be of minor importance (provided that buildings considered have not an historical and tourism relevance). Air pollution damages to certain ecosystems (acid and nitrogen depositions on forests, parks, lakes and wetlands) have been analysed as well, but it is more difficult to transfer and generalise the results of case studies.
Talking about health effects, those of fuel combustion processes in the various activity sectors (electricity conversion, transport, civil use, etc.) have been extensively analysed by the ExternE EU research project. The main health pollutants linked to combustion processes are particulate matter (PM), sulphur dioxide (SO2) , nitrogen oxides (NOx), the volatile organic compounds family (VOCs) that includes some cancerogenic substances, and traces pollutants such as heavy metals. Air pollution from chemical plants (non combustion air emissions) may have very different health impacts from the qualitative and quantitative point of view.
The most important health impact pathways of combustion processes analysed by ExternE (more than eighty) may be grouped in this way:
- mortality and morbidity effects of particulate matter (a long term exposure effect and an immediate short term effect are distinguished by the epidemiological review made within ExternE)
- mortality and morbidity effects of sulphur dioxide (direct and indirect effect are distinguished, since aerosol sulphates originating from SO2 are considered to be harmful as primary particles)
- mortality and morbidity effects of aerosol nitrates produced by Nitrogen oxides emissions (in this case only the indirect effect of NOx is considered, considered to be harmful as primary particles)
- mortality and morbidity effects of ozone, a gas whose formation in the atmosphere is very complex to model, which seems to be formed by the joint effects of NOx, VOCs, NH4 and specific meteorological conditions;
- cancer mortality and morbidity due to specific substances of the VOCs family
External costs valuation allows for a comparison between the various air pollutants’ health effects in the context of the emissions source. ExternE great result has been to valuate the particulate matter (primary and secondary) contribution within the overall health effect of transport air pollution: for example this allowed to highlight the responsibilities of diesel vehicles as compared to gasoline ones either in the urban and in the extraurban contexts. In fact, there is no pollutant more harmful than others in absolute terms. For example CO may be very harmful at very high concentrations in closed environments, but integrated models such as ExternE say that CO concentrations in the open environment are responsible for negligible health damages as compared to other pollutants. The external costs comparison between pollutants depends from the activity intensity, the emissions amount and the context variables, such as the intensity of population exposure.
External costs valuation of air pollution health impacts is based on integrated modelling, the main parts of which are:
a) atmospheric dispersion and chemical transformation model. For example, two models are used by ExternE Transport: Roadpol for the local scale, Ecosense for the regional scale;
b) a screening of best estimates for the various epidemiological effects of human exposure to air pollutants (so called exposure-response functions, that link the increase in the pollutant concentrations to the expected health effect);
c) a selected set of economic damage values for the various type of health effects considered reflecting the economic variables that describe the exposed populations (willingness to pay to avoid the various health effets).