A pragmatic mass closure model for airborne particulate matter at urban background and roadside sites

Twenty-four hour samples of airborne PM10 particulate matter have been collected as coarse and fine fractions using automated dichotomous samplers at four paired roadside and urban background locations in London and Birmingham, UK. The samples have been analysed for sulphate, nitrate, chloride, organic carbon, elemental carbon, iron and calcium and the data have been used to construct a simple model of aerosol chemistry. It is assumed initially that the major components are ammonium sulphate, ammonium nitrate, sodium chloride, elemental carbon, organic carbon and mineral dusts (for which iron and calcium are tracers). This leaves a small proportion of mass unaccounted for, which we attribute to strongly bound water. Increasing the ammonium sulphate and ammonium nitrate content by 29% allows 100% of mass to be accounted for with a high percentage of variance in 24 h mass concentrations explained.