Friday, March 21, 2014

Restrictions on Cars are not Resulting in Expected Reductions in Air Pollution

Why licence plate bans don't cut smog - Car bans such as the one earlier this week in Paris can even make air pollution worse in the long term, analysis shows.
Link to the article @ the Guardian


The Hoy No Circula ('today it doesn't circulate') was introduced by Mexico City in 1989 to combat rampant air pollution. The city bans cars for one day per week, depending on the last number of their number plate. On Mondays five and six don't drive, on Tuesdays it's seven and eight, and so on. The programme was initially successful in bringing down pollution levels, with carbon monoxide (CO) dropping by 11%. But residents began buying second cars (often old inefficient ones) to get around the ban. The long-term impact of the scheme on CO levels has been a 13% rise.


Bogotá's Pico y Placa ('peak and plate') banned cars from driving during the peak traffic hour, two days per week. The Colombians sought to improve on the Mexican model by switching the combinations of days and numbers every year, making it harder to circumvent by buying another car. The policy has failed to deliver clear benefits in air pollution. Restrictions have been tightened periodically, with some of the changes leading to reductions in CO and airborne particles. But one study found most of the major pollutant concentrations were worse because drivers were driving in off-peak hours and driving more to get around the measures.


During the 2008 Olympic Games, Beijing banned cars on the basis of odd and even numbers, similar to the French ban this week. In conjunction with some fortuitous rain and the shutting down of the factories and industries that cause much of Beijing's pollution, the ban drove airborne particulate matter concentrations during the Olympics down by 20%. After the Games, the Beijing authorities kept a one-day a week ban in place. But this, like other long-term licence plate bans, has had a limited effect on air pollution and encouraged drivers to buy second cars.


The Swedish capital implemented its LEZ in 1996. Vehicles are banned from these zones if they fall below certain EU emissions standards . The Stockholm LEZ brought emissions of nitric oxide (NO) and nitrogen dioxide (NO2) down by 20% and particulate emissions down by half. The effect of this on the air quality was noticeable, with NO and NO2 concentrations down 1.3% and particulate concentrations down 3%.


A £5 congestion charge to drive on London's innermost streets was implemented in 2003. Studies showed emissions of dangerous pollutants – NO, NO2 and small particulate matter (PM10) – were reduced by 12%. The charge is now £10.

In 2008, Transport for London introduced an LEZ, which governs the efficiency of lorries, buses and coaches for the whole of Greater London. The zone led to a fall of 20% in tiny particulate matter (PM2.5) but had no discernable impact on PM10 or NO2. Critics say London's LEZ needs to include private vehicles if it is to be effective.


Implemented in 2008, Berlin's LEZ bans all diesel vehicles and petrol vehicles without a closed loop catalytic converter. The effect on levels of diesel pollution, which is a known carcinogen , has been dramatic. Concentrations of diesel particulates have dropped by 14-22%. PM10 concentrations near main roads are down 3% and the number of days when the city's air pollution exceeds European standards has fallen by four to 24 days per year.

No comments: