Exposure concentration levels to ultrafine particles and black carbon along a pedestrian route in Milan

Elevated black carbon (BC) and fine particles concentrations, which have been linked to health problems are typical for urban environments. In Milan, Italy, atmospheric black carbon (BC) concentrations and particle number concentration were measured during December 2013 and July 2014 on two different sampling sites: an urban background site and a 17 km long city track. The resulting dataset was divided into a cold season (84841 BC and PNC data) and warm season dataset (120298 BC and PNC data), covering an overall distance of approximately 1200 km. Samplings took place during morning hours (8:30 – 12:00) and during afternoon hours (15:00 – 18:00) and during all week days except Sundays. Two condensation particle counter (TSI P-trak model 8525) and two micro-aethalometer (AE51) were used for the investigation of seasonal, weekly, daily and spatial variability in an urban environment. After applying noise reduction algorithm on raw data, statistical analysis were applied on the entire dataset. During the cold period, average fixed BC is 3.1 times higher than the respective value for the warm season (1681 ng/m3). Seasonal differences are less marked considering mobile BC, where the ratio between cold period and warm period is 2.0 (3212 ng/m3). Also considering PNC, seasonal variations are evident. Cold period PNC are 2.9 and 2.2 times higher than during the warm period, for the fixed and for the mobile instrument respectively. Daily variations evidence clearly higher values during the morning hours for both seasons. Daily differences are more marked for the PNC than for BC. Street sections without traffic limitations turns out to be more polluted than traffic limited zones, for both considered pollutants. Analysing the congestion charge area (Area C) effect on pollutants concentrations, an higher variation vas observed for BC concentrations compared to PNC. The coefficient of correlation shows a high agreement between mobile and fixed instruments, for both the condensation particle counters and the aethalometers. In both cases a better correlation was found in morning hour data. Good agreement was also found between PNC and BC data. R2 values are higher during the warm period compared to the cold period. Highest correlation values were reached in the most crowded sections, while lowest values were reached in the pedestrian zone (R2RC = 0.69; R2RC = 0.31).