Reducing uncertainties in Ozone formation via Chamber Studies of VOC Oxidation

Lead Research Organisation: University of Leeds
Department Name: Sch of Chemistry

Abstract

Chambers are a vital tool in understanding the chemistry of our atmosphere. They are an ideal vehicle to test proposed mechanisms under simplified, controlled but realistic conditions. The HIRAC (Highly Instrumented Reactor for Atmospheric Chemistry) chamber was constructed during grant NE/C513493/1 and contains several significant features: 1) Uniquely, for an indoor chamber, we can monitor OH and HO2 radicals directly using the FAGE technique. 2) As the chamber is of a stainless steel construction, it is possible to vary pressures over tropospherically relevant conditions. 3) Many important species can be measured by a variety of techniques. This allows us to investigate the possibility of systematic measurement errors. Concentrations of tropospheric ozone are predicted to rise with implications for climate change and air quality. The current proposal seeks to study a number of reactions that are important in determining ozone levels. The mechanims are complex and can only be unravelled via experimental measurements. HIRAC, with a range of complementary detection systems, is an ideal tool to tackle these systems. The reactions to be studied are: 1) Ozone/alkene reactions have been shown to be an important source of OH radicals especially at night. We propose to measure OH and co-product yields as a function of alkene structure in order to construct temperature and pressure dependent structure activity relationships. 2) OH + aromatics - The peroxy radical formed from the attack of OH on the aromatic ring and addition of O2 can react via two channels, either generating a phenol + HO2 (radical regeneration) or ring opening to give dicarbonyl species which are important radical and aerosol precursors. The branching ratio for peroxy radicals formed from reaction of OH with benzene and toluene will be investigated, supported by ab initio calculations. 3) Recent work in our laboratory has identified significant fragmentation of the CH3CO radical formed from OH abstraction of ethanal. If confirmed, this would have important implications for PAN formation. Modelling simulations shown that monitoring CO and CO2 yields should confirm the presence or absence of chemically activated acetyl decomposition under atmospheric conditions. 4) OH + alkynes. The reaction with OH is the major atmospheric removal process for acetylene, an abundant anthropogenic and biomass pollutant. In the prescence of O2, there are two product channels generating glyoxal/OH and HCOOH/HCO. Glyoxal can be photolysed at relatively long wavelengths to give 2HCO radicals and is hence an important HOx source but, being relatively involatile, is also known to be a good aerosol precursor. The atmospheric budget of formic acid is poorly constrained. 5) OH + alkenes. Ethene oxidation is the single largest contributor to European O3 formation. The major uncertainties in this reaction is the rate of reaction of the intially formed hydroxyperoxy radical with NO and the fate of the product alkoxy radical. Both issues can be addressed by product studies in HIRAC As part of the proposal temperature control will be provided for HIRAC to simulate all conditions of the troposphere. One element of the study will be a systematic study (through a tied studentship) of a range of OH, Cl and NO3 reactions via relative and absolute techniques to construct temperature dependent structure activity relationships (SAR). Such SAR are vital in the development of the MCM for temperature dependent modelling of O3 formation and other issues.

Publications

10 25 50

publication icon
Lockhart J (2013) Mechanism of the reaction of OH with alkynes in the presence of oxygen. in The journal of physical chemistry. A

publication icon
Winiberg Frank A. F. (2016) Direct measurements of OH and other product yields from the HO(2)aEuro- +aEuro-CH3C(O)O-2 reaction in ATMOSPHERIC CHEMISTRY AND PHYSICS

 
Description This project focused at looking at key reactions that contributed to the generation of O3 (a harmful pollutant and contributor to global warming) in the troposphere. The project utilized an advanced atmospheric chamber and an initial component of the project was to install a new laser system for OH and HO2 (key atmospheric intermediates) detection and to make the chamber temperature controllable. Following the instrumental upgrades we have successfully examined the following relevant reaction systems:

O3 + isoprene, looking at OH and HO2 detection

OH + alkyne reactions

OH + acetaldehyde.

Additionally we have also developed a new method for pressure dependent calibration of OH and HO2 detection.
Exploitation Route Explotation has been through academic publications and conference presentations. Two publications and 3 PhD thesis have been published. A further publication has been accepted in ACP.
Sectors Environment

URL http://www.chem.leeds.ac.uk/HIRAC/
 
Description Work performed as part of this project has enhanced our understanding of ozone reactions in the troposphere and of oxidative chemistry in general. Outputs from the project have been included in the master chemical mechanism (MCM) which is an important tool linking to policy (e.g. modelling ozone forming potentials). Ozone formation links strongly to air quality (and hence health) and also contributes significantly to radiative forcing.
First Year Of Impact 2011
Sector Environment
Impact Types Policy & public services

 
Description EUROCHAMP 2020
Amount £3,000,000 (GBP)
Funding ID 730997 
Organisation European Commission 
Department Horizon 2020
Sector Public
Country European Union (EU)
Start 12/2016 
End 12/2020
 
Description Equipment Grant associated with BioEnergy CDT at University of Leeds
Amount £110,000 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 11/2014 
End 06/2015
 
Description Marie Curie Fellowship Award
Amount £300,000 (GBP)
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 07/2013 
End 06/2015
 
Description EUROCHAMP Activity 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Participants in your research and patient groups
Results and Impact Outreach and collaboration with other researchers across Europe. Hosted visitors from Germany and Spain.

Publications and research collaborations
Year(s) Of Engagement Activity 2012,2013,2014