Size distributions of fine and ultrafine particles in the city of Strasbourg: Correlation between number of particles and concentrations of NOx and SO2 gases and some soluble ions concentration determination

An Electrical Low Pressure Impactor (ELPI) was used during spring and autumn 2003 in the centre of Strasbourg for the measurement of atmospheric aerosols size distribution. The concentration of NOx and SO2 in air was simultaneously measured with specific analysers. Samples were collected in the range 0.007–10 μm in equivalent aerodynamic diameter size. Number distributions are representative of a pollution originating from urban traffic with a particle size distribution exhibiting a nucleation mode below 29 nm and an accumulation mode around 80 nm in size. A mean particle density equal to 39000±35000 total particles per cm3 with a size ranging from 7 to 10 μm was obtained after a sampling period of 2 weeks in spring. About 86.9% of the number of particles have an aerodynamic diameter below 0.1 μm and 13.1% between 0.1 and 1 μm. Correlation coefficients between the number of particles impacted on each ELPI plate and gas concentrations (SO2 and NOx) showed that the numbers of particles with diameter between 0.10 and 0.62 μm are highly related to the NOx concentration. This result indicates that particles are traffic induced since NOx is mainly emitted by cars as shown by measurements on various sites. Particles are less clearly correlated to the SO2 concentration.Particle analysis on different ELPI plates for a sampling period of 2 weeks in autumn showed high level of soluble NO3−, SO42− and NH4+ ions. Indeed, up to 90% b.w. of these three species were found in the particle range 0.1–1 μm. The formation of particulate NH4NO3 is favoured by high NOx concentration, which induces the formation of gaseous HNO3.