ROXMAS (ROx Chemical Conversion/CIMS), a novel method for atmospheric speciated measurements of HO2 and the sum of organic peroxy radicals (SRO2) developed by MPI-K, has been successfully deployed in a field campaign on Monte Cimone, Italy, June-July 2000. The method relies on amplifying chemical conversion of peroxy radicals to gaseous sulfuric acid via the chain reaction with NO and SO2 and detection of the sulfuric acid by CIMS. Speciated measurements have been realized by diluting atmospheric air in either N2 or O2 buffer, thus exploiting the dependence of the conversion efficiency of RO2 to HO2 on [O2], [NO], and [SO2]. Speciated measurements of HO2 and RO2 are required to provide further insight into radical partitioning and thus to elucidate further the mechanisms of the oxidation of volatile organic compounds in the troposphere. This methodology yields useful speciated results for atmospheric conditions where CH3O2 makes a major contribution to total RO2. Under other conditions it gives an upper limit for [HO2] and a lower limit for [SRO2].

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 HNO3 and SO2 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. HNO3 and SO2 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 HNO3 is a very sticky compound special care was paid for the air-sampling and background-measurement 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 HNO3 by atmospheric mineral-dust aerosol particles.

A 5 weeks experiment (1 June to 5 July 2000) took place at a mountain site, Mt Cimone (44º11' N, 10º42' E, 2165 m a.s.l.), that is representative of Southern Europe background conditions. During this field campaign, a comprehensive characterisation of trace gases and radicals, involved in the production and destruction of O3, as well as of chemical, physical and optical properties of the aerosol was done. Atmospheric gases and aerosols were measured continuously over the 5 weeks period, in order to characterize their background concentrations in the free troposphere and their respective differences in air containing dust aerosols advected from Africa. Due to its location and elevation, Mt Cimone gets free tropospheric air both from the Mediterranean and from the Po Valley, which makes it an invaluable place to study gas/aerosol interactions. A global chemical model coupled to a GCM was used to simulate based upon ECMWF reanalysis the ozone over the region during the period of the field study. The heterogeneous reactions of O3, N2O5, HNO3 and NO3 were accounted for. We estimate that during the field campaign, the effect of heterogeous reactions was to reduce by 8 to 10% the ozone concentration at MTC in cases when air had passed over the Mediterranean Sea. When air was coming from the Atlantic or continental Europe, the reduction of ozone is still 4%. This reduction is mostly due to the large uptake of HNO3 and is the the topic of ongoing work to assess how it affects the global cycle of O3 and the global nitrogen budget.