Modelling Past and Future Changes in Secondary Inorganic Aerosol Concentrations in the UK

Abstract

The FRAME (Fine Resolution Atmospheric Multi-pollutant Exchange) model is a Lagrangian atmospheric transport model with a horizontal grid resolution of 5 × 5 km². This work uses FRAME to calculate annual average concentrations of three secondary inorganic aerosol species (NH₄ ⁺, NO₃ ⁻, SO₄ ²⁻) and gas phase SO₂ over the United Kingdom for the years 2000–2010. Modelled concentrations are compared to measurements from 12 monitoring sites which are operated with the UK Eutrophying and Acidifying Air Pollutants (UKEAP) Acid Gases and Aerosols Network (AGANet). The results showed good spatial correlation between measurements of gas and aerosol concentrations and modelled values (R² > 0.8). However FRAME underestimated decreases in sulphate and ammonium aerosol concentrations over the 11-year period and overestimated changes in SO₂ concentrations relative to measurements. Ongoing work to investigate temporal changes in atmospheric oxidation rates should clarify this difference. FRAME showed a more modest reduction in nitrate concentrations (compared to ammonium and sulphate), which is in agreement with measurements.

FRAME was used to estimate air concentrations for two future scenarios based on emissions predictions for the years 2020 and 2030 in which significant reductions in UK emissions in the UK are forecast (40 % for SO₂ and 47 % for NO_x between 2010 and 2030). The relationships between long term changes in precursor gas emissions and the formation of secondary inorganic aerosol are discussed in terms of the modelling results.