Local Atmospheric Ozone Production Perturbation Instrument - Proof of Concept

Ozone is a major pollutant in the lower atmosphere, known to be harmful to human health, ecosystems, vegetation and certain materials. Ozone is produced as a consequence of the atmospheric degradation of VOCs (Volatile Organic Compounds) in the presence of oxides of nitrogen (NOx). As ozone is a secondary pollutant, control of ozone levels is not straightforward, with ozone production rate showing a highly non-linear dependence upon NOx and VOC levels. Detailed atmospheric chemistry models may be used to inform air quality strategies for ozone abatement, however the link between model predictions, emission controls and ozone production rates is hard to evaluate, as a combination of in situ ozone production, local chemical effects and transport all contribute to variations in ozone levels at a given site. Moreover, even the most detailed models (or measurements) cannot incorporate all atmospheric processes (or species), and model mechanisms are subject to ongoing development. The aim of this project is to test a new approach to directly measure the local atmospheric ozone production rate, and its dependence upon chemical and physical conditions. By perturbing the ambient chemical conditions (for example, through addition of NOx or VOCs), and measuring the effect of the perturbation upon the local ozone production rate, this technology will allow the efficacy of air quality strategies to be directly evaluated (and the importance of local production vs. transport determined). By comparing the measured (and perturbed) ozone production rate with that predicted using atmospheric models, our understanding of the underlying chemical processes may be tested. The fundamental approach will be to sample ambient air into reactors with residence times of a few minutes, exposed to either ambient light or ambient light with the UV component removed. In the former, ozone production continues as in the ambient atmosphere, while in the latter, the ozone production chemistry is switched off by excluding UV light, allowing an ozone baseline to be determined. By comparing the ozone levels exiting each reactor (strictly, O3 + NO2), the in situ ozone production rate may be deduced. By adding reagents to the sampled airstream, the effects of perturbations to the ambient conditions may be investigated and the extent of VOC vs. NOx control may be established. By illuminating the chambers artificially with a controlled spectral distribution, the importance of different chemical mechanisms driving ozone production may be tested. The project will deliver proof-of concept data for a new approach to perform perturbed ozone production rate measurements. Future development of this technology will enable atmospheric measurements which will improve our understanding of the rate of, and most efficient controls upon, atmospheric ozone production. Such measurements will be of considerable use to atmospheric scientists, policy makers and air quality practitioners.