A probabilistic source attribution model for nanoparticles in air suspension applied on the main roads of Madrid and Mexico City

In the first part, we present a simple Probabilistic Source Attribution (PSA) procedure, which allows an estimate of the percentage of the contribution of previously defined sources to the total particulate air pollution determined by a simple field measurement. Four kinds of air pollution sources of small particles (size in the nanometre range, certainly less than 1 μm) can be distinguished on the main roads. The distinction is based on different physical and chemical surface properties of the particles observable via the ratio of the signals provided by two portable sensors with different operating principles (photoelectric charging (PC) and diffusion charging). In the second part, we apply PSA to on-road measurements in Mexico City and Madrid in the years 1999–2001, and in Madrid again in the year 2006. The results show a change in the main source of nanometric particles in Madrid from the period 1999–2001 to 2006 associated with a reduction in the nanoparticulate air pollution by a factor of 3. From the measurement performed in Mexico City, we were able to deduce that a small percentage of one source type (called superpolluters) contributes strongly to the total measured air pollution.