Abstract. Atmospheric gaseous sulphuric acid was measured and its influence on particle formation and growth was investigated building on aerosol data. The measurements were part of the EU-project QUEST and took place at two different measurement sites in Northern and Central Europe (Hyytiälä, Finland, March-April 2003 and Heidelberg, Germany, March-April 2004). From a comprehensive data set including sulphuric acid, particle number size distributions and meteorological data, particle growth rates, particle formation rates and source rates of condensable vapors were inferred. Growth rates were determined in two different ways, from particle size distributions as well as from a so-called timeshift analysis. Moreover, correlations between sulphuric acid and particle number concentration between 3 and 6 nm were examined and the influence of air masses of different origin was investigated. Measured maximum concentrations of sulphuric acid were in the range from 1×10 6 to 16×10 6 cm −3 . The gaseous sulphuric acid lifetime with respect to condensation on aerosol particles ranged from 2 to 33 min in Hyytiälä and from 0.5 to 8 min in Heidelberg. Most calculated values (growth rates, formation rates, vapor source rates) were considerably higher in Central Europe (Heidelberg), due to the more polluted air and higher preexistent aerosol concentrations. Close correlations between H 2 SO 4 and nucleation mode particles (size range: 3-6 nm) were found on most days at both sites. The percentage contribution of sulphuric acid to particle growth was below 10% at both places and to initial growth below 20%. An air mass analysis indicated that at Heidelberg new particles were formed predominantly in air advected from southwesterly directions.

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Abstract. The EU-project MINATROC (MINeral dust And TROpospheric Chemistry) aims at enabling an estimation of the influence of mineral dust, a major, but to date largely ignored component of tropospheric aerosol, on tropospheric oxidant cycles. Within the scope of this project continuous atmospheric measurements of gas-phase HNO 3 and SO 2 were conducted in June and July 2000 at the CNR WMO station, situated on Monte Cimone (MTC) (44 • 11 N -10 • 42 E, 2165 m asl), Italy. African air transporting dust is occasionally advected over the Mediterranean Sea to the site, thus mineral aerosol emitted from Africa will encounter polluted air masses and provide ideal conditions to study their interactions. HNO 3 and SO 2 were measured with an improved CIMS (chemical ionization mass spectrometry) system for ground-based measurements that was developed and built at MPI-K Heidelberg. Since HNO 3 is a very sticky compound special care was paid for the air-sampling and backgroundmeasurement system. Complete data sets could be obtained before, during and after major dust intrusions. For the first time these measurements might provide a strong observational indication of efficient uptake of gas-phase HNO 3 by atmospheric mineral-dust aerosol particles.

[1] Mineral dust, one of the most abundant aerosols by mass in the atmosphere, may have a lasting but to date almost unexplored effect on the trace gases nitric acid (HNO 3 ) and sulfur dioxide (SO 2 ). These gases have an important influence on, for example, the tropospheric ozone cycle, aerosol formation or acid rain. Within the second part of the MINATROC project (Mineral Dust and Tropospheric Chemistry) we investigated the interaction of mineral dust with gaseous HNO 3 and SO 2 . The measurements were performed on a high mountain plateau (Izaña, Tenerife, 2367 m asl) using the highly sensitive CIMS (Chemical Ionization Mass Spectrometry) technique. During five periods of medium and one period of high atmospheric dust load, the HNO 3 concentration decreased with increasing dust concentrations, and in all cases the HNO 3 detection limit was reached. From the HNO 3 decrease the uptake coefficient g HNO 3 was calculated for the first time on the basis of in situ measurements. For the observed events, g HNO 3 varied between 0.017 and 0.054. Moreover, during the dust events a significant decrease of ozone (O 3 ) of the order of 30% was detected. The measurements and the analyses made in this paper show that the direct uptake of O 3 on dust is a minor pathway for O 3 depletion compared to the indirect effect, i.e., HNO 3 depletion on dust which takes away a source of the O 3 precursors nitrogen oxides. In contrast, a general interaction between SO 2 and mineral dust was not observed. Positive as well as negative and no correlations between SO 2 and mineral dust were detected.Citation: Umann, B., F. Arnold, C. Schaal, M. Hanke, J. Uecker, H. Aufmhoff, Y. Balkanski, and R. Van Dingenen (2005), Interaction of mineral dust with gas phase nitric acid and sulfur dioxide during the MINATROC II field campaign: First estimate of the uptake coefficient g HNO 3 from atmospheric data,

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