Modelling the source contribution in the urban background of major air pollutants for 10 European cities in near-real time with LOTOS-EUROS

Air quality is a key aspect of present environmental discussions. Due to the global networking of individual mobility and goods traffic as well as the long-distance transport of pollutants, air pollution now has not only a regional but also continental, European, and intercontinental dimensions. Today, millions of people currently living in polluted regions and are exposed to concentration levels of particulate matter and nitrogen oxides, leading to increased mortality rates. To protect human health, limit values have been set throughout Europe. The newly proposed limit values by the European commission for nitrogen dioxide and particulate matter are currently exceeded in most cities in Europe.

Substantial health benefits may be achieved through political mitigation strategies. This requires a strategy for monitoring cross-border air pollution and quantifying the contributions by source groups and regions of origin. For area-wide analyses and statements detailed, temporally and spatially high-resolution approaches based on chemistry transport models (CTMs) are typically carried out. CTMs aim to reproduce observed pollution variability as good as possible and can be used to forecast air pollution. CTMs can further be used to perform source attribution studies. However, near real-time (NRT) information on the contribution to air pollutants for different emission sources is so far limited.

Within the MI-TRAP project, we are setting up a NRT transport-oriented source apportionment service by provision of a daily analyses of hourly averaged concentrations of the priority pollutants (PM_2.5, PM₁₀, NO and NO₂) in the urban background. By avoiding the use of city-specific proprietary data we will create a highly scalable solution for NRT mapping for cities in Europe. Through a nesting procedure we will provide the information of the background concentration in 10 cities on a ~1x1 km² horizontal grid resolution. The LOTOS EUROS model is used in a NRT operational configuration with meteorological input data from the German Weather Service (DWD) and with emissions as provided through CAMS-REG. Local emissions will be incorporated after a separate NRT emission modelling.

We will calculate the contribution of the different transport modes at the urban background scale using the source apportionment functionality of the LOTOS-EUROS model. The model contains a labelling approach for particulate matter and nitrogen oxides, allowing to flexibly track the contributions of predefined source categories for regions, sectors or combinations thereof. The contributions are calculated and tracked for each process description in the model and are valid for current atmospheric conditions, since all chemical transformations occur at the same concentrations of oxidants.

First results show that combustion processes from traffic, industry & energy production and residential heating are the most important domestic sources. The contributions from residential combustion, energy & industry, shipping and agriculture vary significantly from region to region and between the seasons. The largest variation from day to day and between night and day were observed for road transport. The contribution from non-road transport is most important along the main shipping routes.

We aim to present the results of the first model simulations and its evaluation against observations at the conference.