acid was the limiting reagent in urban ammonium nitrate PM formation. In contrast, NOx ... for base run (std) and for 50% reduced NH3 emissions (eNH3x0.5) ...
Cite abstract as Author(s) (2007), Title, European Aerosol Conference 2007, Salzburg, Abstract T12A041
Sensitivity of urban and rural Ammonium-Nitrate Particulate Matter to Precursor Emissions in Southern Germany U. Uhrner1, S. Drechsler2, R. Wolke3, P.J. Sturm1 and A. Wiedensohler3 1
Traffic and Environment, VKM-THD, Technical University of Graz, Inffeldgasse 81, 8010, Graz, Austria 2 LUBW, Hertzstrasse 173, 76187, Karlsruhe, Germany 3 IfT, Permoserstrasse 15, 04318, Leipzig, Germany Keywords: Particulate Mass, Ammonium nitrate, Aerosol modelling, Emissions, Growth
Fine particulate matter (PM10, PM2.5) is considered as one of the most important pollutants regarding health effects. European standards for PM10 (40 µg/m³ annual mean, max. 35 days above 50 µg/m³ as daily mean; 2nd daughter directive EC/30/99) are difficult to meet in most European cities. During winter time, a significant fraction of PM10 consists of inorganic species, in particular ammonium nitrate and ammonium sulphate. An inorganic fraction of approximately one third is frequently found in PM10 probes. During an air pollution episode, the inorganic fraction exceeded 40 μgm-3 at a busy road in the city centre of Stuttgart in February 2005 (Drechsler et al., 2006). The inorganic fraction was mainly composed of ammonium nitrate and to a lesser extent of sulphate, indicating a major impact of NOx emissions and photochemical reactions on secondary aerosol formation. The sensitivity of secondary ammonium nitrate formation was investigated using a box model approach for the urban area of Stuttgart and the neighbouring rural area Rems-Murr Kreis. The model was used to simulate atmospheric chemistry (Stockwell et al., 1997) and gas/particle partitioning of inorganic compounds (Nenes et al., 1999). Emissions from the detailed UMEG (2004) emission inventory were used. The evolution of the simulated urban particulate matter (PM) ammonium nitrate was found to be highly sensitive to changes in ammonia emissions (see Figure 1). Ammonia, rather than nitric acid was the limiting reagent in urban ammonium nitrate PM formation. In contrast, NOx emissions and hence nitric acid was the limiting reagent in the rural case (see Figure 2). Another important parameter in the sensitivity studies is the assumed well mixed layer used within these box model simulations. Decreasing mixing layers lead to stronger ammonium nitrate formation. The overall behaviour of these model sensitivity studies agrees qualitatively well with composition resolved PM10 measurements taken next to a busy road (ATV ~80000) in Stuttgart and mixing height computations for the aforementioned episode.
Figure 1. Simulated evolution particulate NO3 & NH4 for base run (std) and for 50% reduced NH3 emissions (eNH3x0.5), Stuttgart case.
Figure 2. PM NO3 & NH4 for base run (std) and for 50% reduced NOx emissions (eNO x 0.5), RemsMurr district case. Drechsler, S., Ahrens, D, Lumpp, R., Holst, T. und Uhrner, U., Hohe Feinstaubbelastung als Folge sekundärer Aerosolbildung, Zeitschrift „Immissionsschutz, 06/2006. Nenes, A., Pandis, S. N., and Pilinis, C., Continued development and testing of a new thermodynamic aerosol module for urban and regional air quality models, Atmos. Environ. 33, 1553-1560, 1999. Stockwell, W. R., Kirchner, F., Kuhn, M., and Seefeld, S., A new mechanism for regional atmospheric chemistry modeling, JGR, 102, D22, 25847-25879, 1997. UMEG (2004) Bericht-Nr.4-04/2004 LuftschadstoffEmissionskataster Baden-Württemberg (air pollution emission data base) 2002.
