Along the roads and sidewalks they spread small crushed stones, road salt when the plough. Couple that with carbon soot. They banned fire places which helps but emissions from chimneys, vehicles, and pollution are still there. On a dry day, traffic kicks up a lot of this road dust that you can see in the air. It isn't good to breath as it irritates the nasals. Micro bugs can be in the particles and make you sick. Some days I wear a mask outside by heavily used roads. The city does send street sweeping and vacuum machines out to clean the roads and sidewalks but it literally takes till summer to clean it all up. They usually have to repaint all the lines on the roads each year. In the spring they can be worn off in some places with makes driving harder.
Anyway, a good rain over several days can go a long way to deal with the small crushed stones and dust. The timing is perfect they year. Most of the snow and ice has melted with it's help.