Size distributions of mass and chemical components in street-level and rooftop PM 1 particles in Helsinki

Abstract

In June 1997, five pairs of simultaneous 24 h atmospheric aerosol samples were collected on working days using Berner low-pressure impactors at 3.5 and 20 m heights at an urban site in Helsinki, Finland. The weather was dry and sunny during the campaign. The results were compared to earlier observations made at the lower site. Average submicron masses were 11 μg/m 3 at both heights. Local vehicle exhaust emissions seemed to accumulate particulate mass especially in the 0.15–0.4 μm size range with the average mass concentration being 12% higher at street level for 0.24 μm particles. Long-range transport and sea salt were important for the 0.4–1.3 μm particles leading to slightly higher average mass concentration at the rooftop site for this size-range. Average concentrations of most components, including mass and sulphate, were higher at the rooftop site in the 0.07–0.15 μm size range suggesting that regional or long-range-transported particles and/or local high-level sources might have enhanced these concentrations at the rooftop site. Average submicron concentrations of Cu, Ba, Fe, Sb, Bi, Al and nitrate were higher at street level suggesting that local traffic and road dust were important sources for these components. Concentrations of Ca, Co, Li, Mo, Na, Ni, Pb, Rb, Se, Sr, Ti, Tl, V, MSA, pyruvate, succinate, malonate, SO 4 2−, Cl −, Na +, K + and Ca 2+ were similar at the two heights or higher at the rooftop site pointing to long-range transport and/or local high-level sources. Comparison of size distributions and concentrations revealed several groups of correlating chemical components: (1) SO 4 2−, oxalate, NH 4 + and methane sulphonate, (2) Tl, As, K +, Cd, B, glutarate, succinate and Pb, (3) V, Ni, and, to a lesser extent, Co and Mo, (4) Ba, Cu, Fe and Sb, and (5) Zn, Rb, Pb and Mo. The suggested principal sources for the above groups are (1) long-range transport, (2) mainly long-range transport with some local contribution, (3) local oil combustion, (4) vehicle exhaust and brake wear, and (5) various local sources and long-range transport.