Particulate matter, gas-phase and particle-bound polycyclic aromatic hydrocarbons in an urban environment heavily impacted by vehicular traffic (Bologna, Italy)

A set of 8 polycyclic aromatic hydrocarbons (PAHs) has been analysed in a traffic-limited area in Bologna downtown, both in the gas-phase and in the particulate phase (PM10), and gas-to-particle partitioning has been investigated. From Sep 2002 to May 2003, 28 high volume PM10 samplings were carried out, and in 50 % of the samplings, PM10 concentrations exceeded the limit of 50 microg/m3 established by a 1999 EU directive. A precisely defined sampling strategy was adopted to limit artifacts (8 h sampling in the same time interval) in the 28 samplings carried out in different meteorological conditions. A linear log-log correlation was found between gas-particle partitioning coefficients KBp and the subcooled liquid vapour pressures pB0LB, with rP2P = 0.82 and slope = -0.59. This empirical correlation may be used to anticipate the total (gas + particle-bound) concentration of each PAHs in this urban site, once PM10 and the particle-bound concentration is measured. Parallel samplings of PM10 and of PM2.5 allowed us to ascertain that PM2.5 represents the gross contribution to PM10 and that most of the particle-bound PAHs reside on the finest fraction of particulate matter.