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Impacts of climate change on air pollution levels in the Northern Hemisphere with special focus on Europe and the Arctic - (NERI)

PhD project for Gitte Brandt Hedegaard

Project description

A PhD study carried out within the COGCI PhD School

Main goal and hypotheses

The main goal of this PhD work is to understand and quantify the involved processes and subsequent impacts of a future changing climate on future air pollution concentrations and depositions in the 21st century.

The main hypothesis is that a future changing climate will have an impact on future air pollution concentrations and depositions of important chemical species in different parts of the world. The work will be based on the coupling of a climate model with a long-range chemical transport model and running the coupled system for several centuries (1860-2100). The coupled system will furthermore be used for sensitivity studies in order to test a large set of sub-hypotheses.


Present concentration and deposition levels of air pollution have serious impacts on human health and on natural terrestrial and marine ecosystems. Any changes (decrease or increase) in the general air pollution levels will have positive or negative impacts on health or ecosystems. Especially in pristine areas like the Arctic, the sensitivity to any changes is large. The weather has substantial influence on the chemical composition of the atmosphere. A climate change can therefore have vital importance for future air pollution levels as well as the changes in the anthropogenic emissions. It is important to be able to distinguish between the effects from climate change and emissions projections. Until now a lot of studies have been addressing future emission reduction scenarios and its consequences (see e.g. Bach et al., 2006). However, only a few studies on the isolated effects of a changing climate on air pollution concentrations and depositions exists, and these studies only examines the impacts from single processes at the time, (see e.g. Prather et al., 2003; Hogrefe et al., 2004; Johnson et al., 2001; Zlatev and Brandt, 2005). For example, Hogrefe et al., 2004, used a regional model centered over the eastern USA and showed that the effect from a changed climate may contribute as equal to the air pollution levels in the future as the effects from changed emissions and growing intercontinental transport.

A more multieffect approach is needed where all processes and impacts are studied simultaneously (see e.g. Hedegaard, 2006; Langner et al., 2005; Murazaki and Hess, 2006). Nearly all processes involved in the chemical composition of the atmosphere are dependent on the weather and thereby also on climate change. Atmospheric transport and transport patterns including the horizontal and vertical mixing is directly determined by the different weather parameters as e.g. wind, convection, mixing properties in the ABL, solar radiation, temperature, and heat fluxes, etc. The atmospheric chemical reactions and photolysis rates are determined e.g. by the humidity, global radiation as function of the cloud cover and type, temperature, albedo, etc. Furthermore, the precipitation frequency and amount and the surface properties have great influence on the wet and dry deposition levels. At last there are several parameters that have a large influence on the emissions, as e.g. the temperature dependence of natural emissions of volatile organic compounds (VOC's) and the temperature dependence of anthropogenic emissions from domestic heating, power consumption, etc. Natural emissions of NOx also depends on the weather, e.g. from lightning or from soil.

Description of work and methodology

The PhD project will be based on the coupling of the climate change models ECHAM5 and HIRHAM with the nested long-range chemical transport air pollution model, the Danish Eulerian Hemispheric Model (DEHM). This will form the basic tool for investigating the importance of the different physical/chemical parameters for assessing the impacts of climate change on air pollution levels and its effects on ecosystems and human health.

DEHM is an Eulerian model covering the northern Hemisphere, presently with 150 km x 150 km resolution. The model has two-way nesting capabilities giving the opportunity to calculate results with higher resolution over limited areas, as e.g. Europe. The coupling to the HIRHAM model furthermore provides the basis for studying the effects with greater regional details over Europe. DEHM exists in different versions including different set of chemical species giving the capability to study the impacts of photo-oxidants, particles, POPs and heavy metals including mercury.

As a starting point the coupling will be one way, i.e. output data from the climate model(s) will be used to drive the air pollution models. During the project it is envisaged that steps towards a two-way coupling of the regional climate model HIRHAM and the air pollution model DEHM will be initialised in order to identify relevant feedbacks between pollutants and meteorological processes, and therefore the climate. This would also make a feasible scientific foundation for improving the climate model with more detailed and comprehensive description of some green house gases (e.g. ozone or methane) and particles, which at the moment is relatively simple described in climate models.

Since the natural emissions might be very important in the impact studies, a further development of biogenic and natural emission models in DEHM model is needed. These includes the model for biogenic VOC emissions for isoprene and an extension with terpenes, NOx emissions from lightning discharging and from soil, particles from forest fires, studies of natural emissions from the ocean and further development of models for air/sea exchange for e.g. DMS, NH3, halogens, etc.

Coupling the climate models with the chemical transport model gives the unique possibility of studying the effects of real climate changes including multiple weather parameters on air pollution levels. However, in order to understand and quantify the effects from a single parameter, a large amount of sensitivity studies are also needed. For example, it is hypothesized that climate change will have a large influence on the typical atmospheric transport patterns. The signal from a change in transport patterns will be difficult to distinguish from other important processes in the model results from the full coupled model system. Therefore, it is necessary to carry out a great number of sensitivity studies where all parameters are kept constant except the parameter under examination. In this way it is possible to test a lot of weather parameter oriented hypotheses, and to answer questions connected to each parameter, as e.g.: 1) What are the key meteorological parameters, which are assumed to change with a changing climate that has greatest influence on the future air pollution levels and how large are the impacts? 2) What is the impact of changing atmospheric transport pathways on air pollution concentrations and depositions in the Arctic? 3) What are the impacts of increasing temperatures on the natural emissions of VOCs and NOx? 4) What are the impacts of a shift in precipitation levels and frequency on air pollution concentrations and depositions?


The project will be carried out as a co-operation between University of Copenhagen, NERI and DMI, where supervisors have already been assigned. Furthermore, the PhD project will be formally connected to the newly formed Centre of Energy, Environment and Health (CEEH), funded by the Danish Research and Innovations Agency for the period 2007-2011. The PhD project will furthermore contribute to the Arctic Monitoring and Evaluation Programme (AMAP), which already has acknowledged the importance of climate change impacts on air pollution in the Arctic as a key research area. These institutions and formal networks will give ideal scientific working conditions.


Bach, H., M. S. Andersen, J. B. Illerup, F. Møller, K. Birr-Pedersen, J. Brandt, T. Ellermann, L. M. Frohn, K. M. Hansen, F. Palmgren, J. Seested and M. Winther (2006). Vurdering af de samfundsøkonomiske konsekvenser af Kommissionens temastrategi om luftforurening, Faglig rapport fra DMU, Nr 586, 2006.
Hedegaard, G. B. (2006). Impacts of climate change on air pollution levels in the northern hemisphere, Master Thesis, pp. 100., to appear.
Hogrefe, C., Lynn, B., Civerolo, K., Ku, J.-Y., Rosenthal, J., Rosenzweig, C., Goldberg, R., Gaffin, S., Knowlton, K., and Kinney, P. (2004). Simulating changes in regional air pollution over the eastern united states due to changes in global and regional climate and emissions. Journal of Geophysical research, 109:D22301, doi 10.1029/2004JD004690.
Johnson, C., Stevenson, D., Collins, W., and Derwent, R. (2001). Role of climate feedback on methane and ozone studied with a coupled ocean-atmosphere-chemistry model. Geophysical Research Letter, 28(9).
Langner, J., Bergström, R., and Foltescu, V. (2005). Impact of climate change on surface ozone and deposition of sulphur and nitrogen in Europe. Atmospheric Environment, 39:1129{1141.
Murazaki, K. and Hess, P. (2006). How does climate change contribute to surface ozone change over the united states. Journal of Geophysical Research, 111:D05301, doi:10.1029/2005JD005873.
Prather, M., Gauss, M., Berntsen, T., Isaksen, I., Sundet, J., Bey, I., Brasseur, G., Dentener, F., Derwent, R., Stevenson, D., Grenfell, L., Hauglustaine, D., Horowitz, L., Jacob, D., Mickley, L., Lawrence, M., von Kuhlmann, R., Muller, J.-F., Pitari, G., Rogers, H., Johnson, M., Pyle, J., Law, K., van Weele, M., and Wild, O. (2003). Fresh air in the 21st century. Geophysical Research Letters, 30(2):1100.
Zlatev, Z. and Brandt, J. (2005). Impact of climate changes in europe on european pollution levels. Proceedings from the First ACCENT Symposium, Urbino, Italy, page 6.

Dato: 12-Nov-2009