The origin of PM10, PM2.5 and NO2 background levels in Germany with focus on North Rhine-Westphalia

Air pollution is bad for human health and an international problem which is far from being solved. A large portion of the total PM10 and NO2 burden at, e.g., a street canyon, comes from background concentration. To analyse the origin of these background concentrations, simulations for PM10, PM2.5, and NO2 have been performed with the chemical transport model EURAD (EURopean Air pollution Dispersion model system) for the domain of North Rhine-Westfalia (NRW) with different groups of emission sources within NRW switched off. The results allow a better estimation of the kind of measures needed to meet the EU limit values for PM10 and NO2. Additionally, simulations for Germany with and without anthropogenic emissions in Germany have been performed to determine the contribution of transboundary transport to the background concentration in Germany. The model results show that the contribution of the different sources depends upon the area and constituent. 30 to 80% of the background concentration (annual mean) stems from transboundary transport of air pollutants. While at the conurbation Rhine-Ruhr industry is the main contributor for PM10 and PM2.5, and road traffic for NO2, in the rural areas the contribution of industry and road traffic has about the same magnitude for all constituents

An outbreak of Saharan dust causing high PM10 levels north of the Alps.

A pronounced episode of long range transport of Saharan dust occurred from May 27 to June 1 2008. Elevated PM10 concentrations were observed as the particle cloud travelled from Southern France via parts of Italy, Switzerland and Austria to North-West Germany. The main transport of Saharan dust occurred aloft, leading to an uneven distribution of elevated PM10 concentrations at the ground. While most of Austria was affected near ground level, elevated PM10 burdens in Switzerland were only measured at two alpine stations. Chemical analyses and comparison of PM2.5/PM10 ratios revealed a change in the PM10 composition during the transport. While the high PM10 levels in the alpine region were mainly due to Saharan dust, visible in the high amount of PM10 and almost no change in PM2.5, the PM10 maxima in North-West Germany were mainly caused by secondary aerosol and a smaller but still significant share of dust particles. This is confirmed by maxima in the PM2.5 fraction occuring at the same time as the PM10 maxima and a high amount of ammonium nitrate and ammonium sulfate identified by chemical speciation. The exceedances of the European PM10 daily limit value during the episode can thus predominantly be assigned to natural sources in the Alpine region and in Bavaria, but only to a smaller part in North-Western Germany

Impact of Laptev Sea flaw polynyas on the atmospheric boundary layer and ice production using idealized mesoscale simulations

The interaction between polynyas and the atmospheric boundary layer is examined in the Laptev Sea using the regional, non-hydrostatic Consortium for Small-scale Modelling (COSMO) atmosphere model. A thermodynamic sea-ice model is used to consider the response of sea-ice surface temperature to idealized atmospheric forcing. The idealized regimes represent atmospheric conditions that are typical for the Laptev Sea region. Cold wintertime conditions are investigated with sea-ice–ocean temperature differences of up to 40 K. The Laptev Sea flaw polynyas strongly modify the atmospheric boundary layer. Convectively mixed layers reach heights of up to 1200 m above the polynyas with temperature anomalies of more than 5 K. Horizontal transport of heat expands to areas more than 500 km downstream of the polynyas. Strong wind regimes lead to a more shallow mixed layer with strong near-surface modifications, while weaker wind regimes show a deeper, well-mixed convective boundary layer. Shallow mesoscale circulations occur in the vicinity of ice-free and thin-ice covered polynyas. They are forced by large turbulent and radiative heat fluxes from the surface of up to 789 W m−2, strong low-level thermally induced convergence and cold air flow from the orographic structure of the Taimyr Peninsula in the western Laptev Sea region. Based on the surface energy balance we derive potential sea-ice production rates between 8 and 25 cm d−1. These production rates are mainly determined by whether the polynyas are ice-free or covered by thin ice and by the wind strength