Comprehensive Analytical System for Measuring Isoprene-derived Nitrates

A comprehensive understanding of the interactions between the biosphere and the atmosphere is crucial for: (i) Earth System science (ii) predicting the impact of future climate change. Isoprene is the most important biogenic volatile organic compound (VOC) in the atmosphere, with its emissions accounting for 1/3 of the global total VOC emissions (i.e. natural and anthropogenic combined). Through its degradation chemistry, isoprene impacts ozone and the formation of aerosols, which together impact global warming and the atmosphere's ability to cleanse itself of pollutants.

Recent model studies show that the calculated impact of isoprene on ozone is critically dependent on the model isoprene chemical scheme, in particular the way the isoprene derived nitrates are treated. There is considerable uncertainty over how much of these nitrates are formed and what subsequently happens to them. Of particular importance is whether the nitrogen oxides, which are tied up in the nitrates, are later recycled or are lost from the atmosphere. This then impacts the amount of ozone that can be subsequently formed.

Virtually everything that is known about isoprene nitrate chemistry is based on theoretical calculations, with most observational constraints based on measurements of either groups of nitrates as totals, or degradation products that come from more than one reaction and precursor species. For any substantial scientific progress to be made comprehensive measurement of individual nitrates is required, in laboratory studies to properly understand the chemistry of individual nitrates, and in the field to determine the true impact of isoprene on ozone and aerosol.

Studies of isoprene degradation chemistry have been greatly limited by measurement techniques and their inability to identify and quantify individual organic nitrates. We therefore propose to:
1. Develop an analytical gas chromatography mass spectrometry instrument capable of detecting and identifying individual isoprene derived nitrates
2. Synthesise 18 individual isoprene derived nitrates to enable their unambiguous detection and identification and for their concentrations to be quantified down to atmospheric levels.

The final products of this "Technology Led" proposal will be novel synthesis protocols and an analytical system that will allow calibrated measurements of 18 individual isoprene nitrates at concentrations down to atmospheric levels. The system can then subsequently be used in both laboratory and field studies. Such an analytical system will be unique and will enable isoprene chemistry to be studied at the level of individual reactions and products. This will facilitate a major advancement in the evaluation of model chemical mechanisms used to predict air quality and climate. It will enable a step change in the ability to constrain these mechanisms by allowing quantification of the rates and products of individual branches of these reaction schemes. Further it will allow the concentrations of individual isoprene nitrates to be measured in the real atmosphere and models tested against these data. Altogether this will enable the impact of isoprene nitrates on nitrogen oxide recycling and ozone to be quantified with well constrained models.

The elevated ozone in England during the 2003 heatwave was attributed, in part, to elevated concentrations of isoprene. Future changes in climate and land-use are likely to affect isoprene emissions so understanding how isoprene impacts nitrogen oxide recycling is important for predicting future ozone concentrations. The potential advancements in scientific understanding that can be made following the development of the technology within this proposal are therefore essential for policy makers developing emission control strategies.

This technology-led proposal is to develop an analytical system that can be used in future scientific research. Therefore immediate beneficiaries are academic in nature. However the potential benefits that can come from this instrumentation are highly relevant to policy makers developing emission control strategies to comply with air quality standards and to mitigate climate change. As such it is also relevant to the wider UK public, their quality of life and health.

The elevated ozone in England during the 2003 heatwave was attributed, in part, to elevated concentrations of isoprene. At this time around 2000 excess deaths were recorded in England and Wales of which 20-40% were attributed to elevated concentrations of ozone and aerosol. Future changes in climate and land-use are likely to affect isoprene emissions so it is important to understand how isoprene impacts ozone. However even the sign (positive or negative) of this varies between models using different chemical schemes, with the treatment of isoprene nitrates identified as the dominant cause of these discrepancies. For any substantial improvements to be made to these schemes comprehensive measurement of individual nitrates is required. This proposal is to develop an analytical system to measure isoprene nitrates, which subsequently can be used in both laboratory and field studies designed to quantify production and loss rates of these compounds and to evaluate model chemical mechanisms used to predict air quality and climate.

The main impact of this proposal on these end-users is therefore several steps beyond the scope or lifetime of this project. To ensure that the full potential of this work is realised by these end-users, we will ensure the technological advancements are made readily available to the academic beneficiaries and that the new technology is utilised in ways that will lead to improved chemical mechanisms and observationally evaluated models. Engaging with academic beneficiaries is therefore the critical first step along the pathway to the wider end-users.