1Institut für Bio- und Geowissenschaften, IBG-2, Forschungszentrum Jülich, 52425, Jülich, Germany
2Institut für Energie- und Klimaforschung, IEK-8, Forschungszentrum Jülich, 52425, Jülich, Germany
3Institut für Anorganische und Analytische Chemie, Johannes Gutenberg Universität Mainz, 55128, Mainz, Germany
4Weizmann Institute of Science, Rehovot, 76100, Israel
*now at: Department of Physics, Division of Atmospheric Sciences, Helsinki University, PL 64, 00014 Helsingin yliopisto, Finland
**now at: Frankenstrasse 8, 52382 Niederzier, Germany
Abstract. The impact of nitrogen oxides (NOx = NO + NO2) on new particle formation (NPF) and on photochemical ozone production from real plant volatile organic compound (BVOC) emissions was studied in a laboratory set up. At high NOx conditions (BVOC/NOx < 7, NOx > 23 ppb) no new particles were formed. Instead photochemical ozone formation was observed resulting in higher hydroxyl radical (OH) and lower nitrogen monoxide (NO) concentrations. As soon as [NO] was reduced to below 1 ppb by OH reactions, NPF was observed. Adding high amounts of NOx caused NPF orders of magnitude slower than in analogous experiments at low NOx conditions (NOx ~ 300 ppt), although OH concentrations were higher. Varying NO2 photolysis enabled showing that NO was responsible for suppression of NPF suggesting that peroxy radicals are involved in NPF. The rates of NPF and photochemical ozone production were related by power law dependence with an exponent of approximately −2. This exponent indicated that the overall peroxy radical concentration must have been the same whenever NPF appeared. Thus permutation reactions of first generation peroxy radicals cannot be the rate limiting step in NPF from monoterpene oxidation. It was concluded that permutation reactions of higher generation peroxy radical like molecules limit the rate of new particle formation.
In contrast to the strong effects on the particle numbers, the formation of particle mass was less sensitive to NOx concentrations, if at all. Only at very high NOx concentrations yields were reduced by about an order of magnitude.