A research done in my city's main train station showed 400,000 UFP particles per cubic centimetre.
I am looking into printing pamphlets and wanted to inquire how does spending half an hour in a 400,000/cm^3 environment compare with smoking when it comes to lungs damage. It can be a rough estimation, something along the lines of: "Spending half an hour in those conditions is equivalent to smoking 5 cigarettes".
The research: "Measurements of air pollution with nanoparticles and evaluation of the passengers' exposure in the Jerusalem central bus station and in the departing buses and also in the Shalom train station and in the departing trains" (pdf). English starts on page 12.