This weekend, Parisians and those visiting the city will enjoy free public transportation as they move from Versailles to La Tour Eiffel. This initiative comes as much of Northern France experiences dangerously high levels of local air pollution, leaving local governments desperate to get cars off the road.

According to air quality measurements across the country, concentrations of PM10 (particulate matter with diameters of less than 10 microns) are alarmingly high. The country has recommended that residents avoid being outdoors, stay away from intense physical activity, and reduce driving speeds (or avoid driving completely, if possible). In Lower Normandy, air pollution levels have hit record levels.

France is not alone in their struggle with air pollution. In China, air quality concerns have reached a point where some companies are looking to compensate employees for living in these polluted environments. Yesterday, Panasonic announced that it would give its expat workers a wage premium to compensate for the country's hazardous air pollution levels.

One of the primary hazardous air pollutants in both France and China is particulate matter (PM), a mix of liquid and solid particles that can contain sulfates, nitrates, ammonium, carbon, metals, and an array of allergens. PM is described by the size of the particles, measured in micrometers or microns. PM10 is shorthand for particulate matter that is less than 10 microns in diameter. In Europe, 50-70% of PM10 is actually PM2.5. That is, very mix of very fine particles less than 2.5 microns in diameter.

Both PM10 and PM2.5 are regulated in much of the world. The World Health Organization (WHO) sets recommended concentration levels according to the potential health impacts of different pollutants. In the case of particulate matter, these impacts include asthma and other respiratory illnesses, lung cancer and cardiopulmonary mortality. Globally, an estimated 800,000 early deaths occur each year as the result of combustion-related emissions (both particulate matter and ozone).

While these particles can come from non-human sources (e.g. volcanoes), anthropogenic sources are the major contributors in cities. PM10 primarily comes from combustion - in car engines (both diesel and petrol), power plants (coal, lignite, heavy oil and biomass), and other industrial activities (for example mining, the manufacturing of cement, and smelting). Therefore, it makes sense that Paris is trying to get cars of the road as a quick fix to current air quality concerns.

This brings about the question - should public transportation be free in cities that are chronically plagued with air quality troubles?

Using centralized public transportation can help regions to more directly control local air pollution. Cities plagued with air quality problems can switch to cleaner diesel buses and electric trains. Thousands of government-owned buses are certainly easier to clean up than tens of thousands of privately-owned vehicles.

Furthermore - as the French have realized - the same public transportation system can be used to encourage people to keep their cars off the road (and the pollution out of the air) in the first place.

Photo credit:

1. Photo of Eiffel Tower by DavidDennisPhotos via Creative Commons.

2. Photo of Beijing in 2005 after two days of rain and during a smoggy day by Bobak via Wikimedia Commons.