Long-term measurements of OH reactivity

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


Poor air quality has been cited by DEFRA as the greatest environmental risk to public health in the UK, and exposure to air pollution has recently been listed for the first time as a cause of death in a landmark coroner's ruling on the death of a nine year old girl in London. Air pollution has been reported to affect every organ in the body and has been linked to illnesses including cardiovascular and respiratory diseases, vascular dementia, and Alzheimer's disease. Each year, air pollution causes over 4.2 million premature deaths worldwide and costs the UK economy ~£15 billion. The properties of our air are governed by atmospheric composition, the understanding of which is vital to the development of policies aimed at improving air quality.

The composition of the atmosphere is controlled by the emission rates and chemistry of trace species emitted into the atmosphere from a wide range of sources including industry, vehicle exhausts and plants. Emissions of nitrogen oxides and volatile organic compounds (VOCs) into the atmosphere lead to complex cascades of chemical reactions which are predominantly initiated by naturally occurring OH radicals. This chemistry results in the generation of secondary pollutants such as ozone (O3) and secondary organic aerosol (SOA), which impact the climate and are harmful to human health. However, it is only possible to identify and measure the concentrations of a small fraction of the vast array of over 10,000 different atmospheric VOCs, which limits our ability to provide accurate assessments and predictions of air quality.

Despite such challenges, it is possible to quantify the presence and impacts of unmeasured species in the atmosphere. Since most species emitted into the atmosphere react with OH radicals, measurements of the total loss rate of OH radicals in ambient air provides a means to quantify the presence of unmeasured species, and the extent to which they contribute to the production of ozone and SOA. Such measurements of the total OH loss rate are used to define the OH reactivity (kOH), which can be considered to represent the total loading of reactive pollutants in an air mass that oxidise to secondary pollutants.

The capability for long-term measurements of OH reactivity has the potential for development of a new air quality metric that defines the chemical regime in operation for production of secondary pollutants such as ozone and SOA, and enables monitoring of changing trends in pollutant emissions, evaluation of the accuracy and extent to which the reactivity and impacts of pollutants are considered in atmospheric models, and the provision of more accurate air quality forecasts. However, routine and long-term measurements of OH reactivity are hindered by a lack of suitable techniques.

In this work we will develop a novel instrument to make long-term measurements OH reactivity. We will make long-term measurements of OH reactivity at the recently developed NERC urban air quality measurement supersite in Birmingham and use these to evaluate models used to predict atmospheric composition and air quality.

Compared to instruments currently in use for short-term intensive measurement campaigns, the instrument developed in this work will be lighter, cheaper and more mobile, with lower power consumption and lower staffing demands owing to a more rugged and automated design. The instrument will have potential for atmospheric measurements from ground-based, aircraft and shipborne platforms, as well as laboratory measurements in atmospheric simulation chambers and direct measurements of vehicle emissions.

Ultimately, this work will deliver a robust instrument, providing opportunities for widespread measurements of a key parameter in atmospheric chemistry. Increased availability and more widespread use of reactivity measurements in atmospheric models will lead to significant improvements to our understanding of atmospheric composition and air quality.


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