Non-methane Volatile Organic Compounds in the UK
Alastair C. Lewis, David C. Carslaw, Sarah Julia Moller
Abstract
Volatile organic compounds (VOCs) are a broad class of air pollutants which act as precursors to tropospheric ozone and secondary organic aerosols (a component part of PM2.5).The National Atmospheric Inventory (NAEI) indicates that UK emissions of anthropogenic VOCs peaked around 1990 at 2,840 kt yr -1 and then declined to ~810 kt yr -1 in 2017.Notable has been success in reducing emissions from the tailpipe of gasoline vehicles and other evaporative losses of VOCs from fuels (including natural gas) during their production and distribution.Ambient observations of selected VOCs in the Defra Automated Hydrocarbon Network also show significant declines since the 1990s, including species that are emitted directly from fuel loss, such as alkanes and mono-aromatics, and VOCs that are by-products of incomplete combustion such as alkenes and ethyne.The rates of reduction in ambient concentrations slowed around 2010 and have now plateaued.Benzene and 1,3 butadiene have specific limit and target values in the UK and concentrations of these have been successfully reduced such that the UK has reported no exceedances in recent years.Whilst both emissions and concentrations of VOCs have fallen, further reductions in VOC emissions are anticipated for the UK to meet obligations under the National Emission Ceiling Directive in 2030 and UNECE Convention on Long-Range Transport of Air Pollution.