Using mass reconstruction along a four-site transect as a method to interpret PM₁₀ in west-central Scotland, United Kingdom

Concurrent 24-hr samples of particulate matter of median aerodynamic diameter less than 10 μm (PM₁₀) were collected over a 10-day period in August 2000 at four sites along a transect in west-central Scotland, UK (passing from the coast through the city of Glasgow) in line with the prevailing southwesterly wind. Each sample was analyzed for chloride (Cl ^-), nitrate (NO_3-), sulfate (SO₄ ^2-), ammonium (NH₄ ⁺), calcium (Ca ²⁺), iron (Fe), and organic hydrocarbon material (OHM). The contribution from elemental carbon (EC) was estimated. Sampling days were categorized according to local wind direction, synoptic flow, and air mass back trajectories. Chemical mass balance (CMB) reconstruction of the following PM₁₀ components was derived for each wind direction group and at each transect location: ammonium sulfate ((NH₄)₂SO ₄), ammonium nitrate (NH₄NO₃), sodium chloride (NaCl), gypsum (CaSO₄), OHM, EC, soil/surface dusts, and particle-bound water. The results showed that PM₁₀ at the coastal site was dominated by the marine background (NaCl) compared with the urban sites, which were dominated by local primary (EC and soil/resuspension) and secondary sources (NH₄NO₃, (NH₄) ₂SO₄, and OHM). There was evidence of Cl^- depletion as NaCl aerosol passes over urban areas. There was also evidence of longrange transport of primary PM₁₀ (EC and OHM); for example, at the coastal site from transport from Ireland. The work demonstrates how the general approach of combining mass reconstruction along a transect with other information such as wind/air-mass direction generates insight into the sources contributing to PM₁₀ over a more extended spatial scale than at a single receptor.