Abstract
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 setup. At high NOx conditions ([BVOC] / [NOx] < 7, [NOx] > 23 ppb) new particle formation was suppressed. Instead, photochemical ozone formation was observed resulting in higher hydroxyl radical (OH) and lower nitrogen monoxide (NO) concentrations. When [NO] was reduced back to levels below 1 ppb by OH reactions, NPF was observed. Adding high amounts of NOx caused NPF to be slowed by orders of magnitude compared to 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. This suggests that peroxy radicals are involved in NPF. The rates of NPF and photochemical ozone production were related by power law dependence with an exponent approaching −2. This exponent indicated that the overall peroxy radical concentration must have been similar when NPF occurred. 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 intermediates limit the rate of new particle formation. In contrast to the strong effects on the particle numbers, the formation of particle mass was substantially less sensitive to NOx concentrations. If at all, yields were reduced by about an order of magnitude only at very high NOx concentrations.
Highlights
Secondary organic aerosols (SOA) are an important component of tropospheric aerosols, affecting the radiation balance of Earth’s atmosphere either directly by scattering or absorbing incoming sunlight or by acting as cloud condensation nuclei
The impact of nitrogen oxides (NOx = nitrogen monoxide (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 setup
We found that the photochemical system behaved more complicated than expectable from a simplistic approach: assuming that NPF would be controlled by permutation reactions of first-generation peroxy radicals led to contradictions
Summary
Secondary organic aerosols (SOA) are an important component of tropospheric aerosols, affecting the radiation balance of Earth’s atmosphere either directly by scattering or absorbing incoming sunlight or by acting as cloud condensation nuclei. Due to the strong biogenic sources of volatile organic compounds, a large fraction of SOA has natural sources. Plant emitted biogenic volatile organic compounds (BVOC) are oxidized in the atmosphere and the oxidation products condense on preexisting particulate matter, increasing their size and modifying their properties. New particle formation (NPF) has been frequently observed all over the world (Kulmala et al, 2004a), in clean background air (e.g., Dal Maso et al, 2007) as well as in urban atmospheres (e.g., Betha et al, 2013). The mechanisms of NPF are not yet clarified.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
