Concentration levels and source apportionment of ultrafine particles in road microenvironments

摘要: Abstract A mobile laboratory unit (MOBILAB) with on-board instrumentation (Scanning Mobility Particle Sizer, SMPS; Ambient NOx analyzer) was used to measure size-resolved particle number concentrations (PNCs) of quasi-ultrafine particles (UFPs, 9–372 nm), along NOx, in road microenvironments. On-road measurements were carried out and around a large Greek urban agglomeration, the Thessaloniki Metropolitan Area (TMA). Two 2-week measurement campaigns conducted during warm period 2011 cold 2012. During each sampling campaign, MOBILAB driven through 5-day inner-city route second external covering total wide range districts (urban, background, industrial residential), types (major minor roads, freeways, arterial interurban roads). All routes working days, morning afternoon hours under real-world traffic conditions. Spatial classification involved assignment points location bins defined by aspect ratio adjacent street canyons (USCs). Source apportionment further out, applying Positive Matrix Factorization (PMF) size distribution data. Apportioned PMF factors interpreted, employing two-step methodology, which (a) statistical association factor contributions 12 h air-mass back-trajectories ending at TMA measurements, (b) Multiple Linear Regression (MLR) using as dependent variables, while relative humidity, solar radiation flux, vehicle speed independent variables. The applied data analysis showed that low-speed cruise high-load engine operation modes are two dominant sources UFPs most microenvironments TMA, significant from background photochemical processes period, explaining reversed seasonal variation UFP concentrations, compared those observed cities across Northern Europe. It also demonstrated town planning exerts profound effect on mitigation emissions.