The role of long-range transport and domestic emissions in determining atmospheric secondary inorganic particle concentrations across the UK

摘要

Surface concentrations of secondary inorganic particle components over theUK have been analysed for 2001–2010 using the EMEP4UK regional atmosphericchemistry transport model and evaluated against measurements. Gas/particlepartitioning in the EMEP4UK model simulations used a bulk approach, whichmay lead to uncertainties in simulated secondary inorganic aerosol. However,model simulations were able to accurately represent both the long-termdecadal surface concentrations of particle sulfate and nitrate and anepisode in early 2003 of substantially elevated nitrate measured across theUK by the AGANet network. The latter was identified as consisting of threeseparate episodes, each of less than 1 month duration, in February, Marchand April. The primary cause of the elevated nitrate levels across the UKwas meteorological: a persistent high-pressure system, whose varyinglocation impacted the relative importance of transboundary versus domesticemissions. Whilst long-range transport dominated the elevated nitrate inFebruary, in contrast it was domestic emissions that mainly contributed tothe March episode, and for the April episode both domestic emissions andlong-range transport contributed. A prolonged episode such as the one inearly 2003 can have substantial impact on annual average concentrations. Theepisode led to annual concentration differences at the regional scale ofsimilar magnitude to those driven by long-term changes in precursoremissions over the full decade investigated here. The results demonstratethat a substantial part of the UK, particularly the south and southeast,may be close to or exceeding annual mean limit values because of import ofinorganic aerosol components from continental Europe under specificconditions. The results reinforce the importance of employing multiple yearsimulations in the assessment of emissions reduction scenarios on particulate matterconcentrations and the need for international agreements to address thetransboundary component of air pollution.