Major component composition of PM_(10) and PM_(2.5) from roadside and urban background sites

摘要

Using dichotomous Partisol samplers, airborne particulate matter has been collected and analysed as PM_(2.5) and PM_(10). The instruments were deployed at four sets of paired roadside and urban background locations, three in London and one in Birmingham (UK) and the sampling protocols aimed to give equal weight to all seasons of the year. In addition to determination of sample mass, concentrations have been determined for major chemical components as follows: sulphate, nitrate, chloride, organic carbon, elemental carbon, iron and calcium. The measured concentrations have been converted to equivalent quantities of ammonium sulphate, ammonium nitrate (in PM_(2.5)), sodium nitrate (in PM_(2.5-10)), sodium chloride, elemental carbon, carbon compounds, gypsum and iron-rich dusts. The mass of strongly bound water has also been calculated following the mass closure methodology of Harrison et al. (Atmos. Environ. 37 (2003) 4927). Examination of the difference between roadside (mean 34.7 μg m~(-3) PM_(10)) and corresponding urban background (mean 23.2 μg m~(-3) PM_(10)) samples indicates average mass increments of 11.5 μg m~(-3) of PM_(10) and 8.0 μg m~(-3) of PM_(2.5) for the four site pairs, and that the roadside particle increment is comprised very largely of elemental carbon, organic compounds and iron-rich dusts. The major component composition lies somewhere between that reported as typical of the eastern and western US. A comparison with PM_(2.5) and PM_(15) sampled in Leeds (UK) in 1982 shows a decline in all major constituents except mineral dusts (PM_(2.5) only). In a comparison of data for days with PM_(10) above the EU 24-h Limit Value of 50 μg m~(-3) with data from all days, the component showing the greatest ratio between high pollution days and all days is fine particle nitrate.