Suppression of air pollution via aerosol mediated removal of peroxy radicals

Air quality is an acute societal concern with around 7 million people dying per year from the combined effect of outdoor and indoor air pollution. Ozone (O3) is a harmful pollutant and this project is associated with the discovery of a new "aerosol inhibited" photochemical O3 regime. For the last 30-years, air quality policy for reducing O3 pollution has split the world into NOx or VOC (volatile organic carbon) limited regimes based on the dominant radical (ROx) chain termination step.

Depending on the regime, policymakers have either reduced NOx or VOC emissions to reduce O3. This has led to substantial reduction in O3 concentrations over Europe and North America. For some parts of the world the dominant chain termination reaction is not one of the standard routes, but rather the reactive removal of the peroxy radical HO2 onto aerosol surfaces, placing these regions into the new "aerosol inhibited" photochemical regime.

There is a strong interaction and hence tension between policies to reduce particulate matter (PM, also damaging to health) and O3. Efforts to reduce PM (aerosol) levels would lead to the unintended consequence of increasing O3 concentration (as might have been seen recently in China). The rates of uptake of HO2 onto aerosols are poorly constrained, and a much better understanding of this ozone regime is necessary to drive the best policy.

In this project a new field instrument for the direct measurement of the rate of removal of peroxy radicals onto aerosols, which when deployed alongside our existing free-radical measurements, will provide a unique capability to understand the real world uptake of radicals onto aerosol. We will make field measurements to enable the formulation of novel parameterizations for heterogeneous removal.

These will be included in models to further understanding O3 regimes important for air quality and climate.

The project is a combination of fieldwork, laboratory studies and numerical modelling, and will have the following specific objectives: (1) To develop a new field instrument to measure the rate of loss of HO2 and some RO2 onto ambient aerosol

(2) To deploy this instrument at the NERC Air Pollution Supersite in Manchester alongside simultaneous measurements of OH, HO2, RO2 and OH reactivity (using FAGE instrumentation), together with a comprehensive suite of supporting gas-phase and radiation measurements, as well as aerosol surface area and aerosol composition, which are all available from the Manchester site

(3) Determine uptake coefficients onto aerosols for HO2 and RO2 from field measurements in (2) and using new laboratory data develop new parameterizations of HO2 and RO2 uptake coefficients.

(4) To incorporate aerosol surface processes into models and use the new parameterizations of uptake coefficients from (3) to quantify aerosol uptake to understand how heterogeneous processes influence our understanding of ozone control policies.

The research will lead to an improved representation of chemical oxidation mechanisms in models that are used for the prediction of future changes in climate and air quality. The student will benefit from using a wide range of instrumentation (lasers, optics, vacuum and gas handling, data acquisition, electronics) and modelling tools, and by working with expert investigators will receive advanced technical training and enhance their skills base considerably.

The Leeds FAGE instrumentation is part of the National Centre for Atmospheric Science. There is scope for further collaboration with atmospheric scientists in Leeds and elsewhere.