Variability of particulate matter concentrations along roads and motorways determined by a moving measurement unit

The spatial variability of aerosol number and mass along roads was determined in different regions (urban, rural and coastal-marine) of the Netherlands. A condensation particle counter (CPC) and an optical aerosol spectrometer (LASX) were installedin a van along with a global positioning system (GPS). Concentrations were measuredwith high-time resolutions while driving allowing investigations not possible with stationary equipment. In particular, this approach proves to be useful to identify those locations where numbers and mass attain high levels (‘hot spots’). In general, concentrations of number andmass of particulate matter increase along with the degree of urbanisation, with number concentration being the more sensitive indicator. The lowest particle numbers and PM1-concentrations are encountered in a coastal andrural area: o5000 cm 3 and6 m gm 3 , respectively. The presence of sea-salt material along the NorthSea coast enhances PM>1-concentrations comparedto inlandlevels. High-particle numbers are encounteredon motorways correlating with traffic intensity; the largest average number concentration is measuredon the ring motorway aroundAmsterd am: about 160 000 cm 3 (traffic intensity 100 000 veh day 1 ). Peak values occur in tunnels where numbers exceed10 6 cm 3 . EnhancedPM 1 levels (i.e. larger than 9m gm 3 ) exist on motorways, major traffic roads and in tunnels. The concentrations of PM>1 appear rather uniformly distributed (below 6m gm 3 for most observations). On the urban scale, (large) spatial variations in concentration can be explainedby varying intensities of traffic andd riving patterns. The highest particle numbers are measuredwhile being in traffic congestions or when behind a heavy diesel-driven vehicle (up to 600 10 3 cm 3 ). Relatively high numbers are observedduring the passages of crossings and, at a decreasing rate, on main roads with much traffic, quiet streets and residential areas with limited traffic. The number concentration exhibits a larger variability than mass: the mass concentration on city roads with much traffic is 12% higher than in a residential area at the edge of the same city while the number of particles changes by a factor of two (due to the presence of the ultrafine particles (aerodynamic diameter o100 nm). It is further indicated that people residing at some 100 m downwind a major traffic source are exposed to (still) 40% more particles than those living in the urban backgroundareas. r 2004 Elsevier Ltd. All rights reserved.