Abstract
Ambient air pollution from PM2.5 is a major risk to human and environmental health, with significant impacts on mortality and morbidity. Mitigation policies—which may be regional or national in extent—need to consider both primary and secondary particles to be effective, balancing within-region emissions and longer-range transport phenomena. The modelling system WRF-CMAQ was used to simulate the impact of emissions reductions in the West Midlands region of the UK, evaluating the change in total PM2.5 and in its primary and secondary components. Domestic combustion, road transport and agriculture emissions were reduced individually or in combination, at a national or at local level. Combined reduction of road transport and agriculture emissions showed the strongest reduction (29%) in average PM2.5 if applied at national level. At the local level, reductions from domestic combustion were shown to be the most effective policy (13.4% on average). Secondary inorganic fractions of PM2.5 are the most abundant, with 25% NO3− 21% SO42− and 13% NH4+ on average. Scenario analysis shows that the contribution of secondary components to the fractional change of PM2.5 dominates for national policies (up to 0.86 for NO3−) when road transport and agriculture activities are reduced, while at the regional level the elemental and organic carbon fractional changes are dominant (up to 0.64 for organic carbon).
Highlights
Within the UK-wide reductions (UK)/European context, some recent studies have focused on the effect of long-range transport of aerosols from northwest Europe to the UK [10,11] while others focused on the sensitivity of final concentrations to primary PM2.5 emission reductions for present and future periods [12]
The simulations using Weather Research and Forecasting (WRF) and Community Multi-Scale Air Quality Model (CMAQ) were conducted for two monthly periods representative of winter and summer conditions of 2016, namely January and July, applyvariables (e.g., U, V, T and Q) calculated by WRF to the original re-analysis value from the data used by WRF (e.g., ECMWF) with a certain frequency of time (e.g., 6 h)
Comparing the difference in PM2.5 reduction from the UK to the West Midlands (WM) case, we find that scenario A leads to, on average, 4.2% difference between national and regional-only emissions changes, while scenarios B and C show a higher difference between these two approaches of around 18%
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Within the UK/European context, some recent studies have focused on the effect of long-range transport of aerosols from northwest Europe to the UK [10,11] while others focused on the sensitivity of final concentrations to primary PM2.5 emission reductions for present and future periods [12]. While some works have focused on high-resolution numerical simulations over the city of London [16,17], none have previously addressed the impact of national vs regional primary PM2.5 emission reductions on total and individual secondary inorganic fractions in the West Midlands.
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