Particular about particulates

IF A fine powder combining arsenic, black carbon, formaldehyde, nickel, sulphur dioxide and nitrogen oxide sounds unpleasant, imagine how it would be if 200 tonnes of it were dumped on your town every day. Imagine, too, that it was proved to be cancerous, with most of it coming in the shape of particles small enough to lodge in the deepest, most tender parts of your lungs. Such is the woe of India’s capital. With a count of “respirable suspended particulate matter” that is roughly double that of China’s notoriously smoggy capital, Beijing, Delhi is ranked by the World Health Organisation (WHO) as the world’s most polluted big city. Several other Indian cities are nearly as atrocious (see table).

Perhaps 25,000-50,000 of greater Delhi’s 25m people die prematurely every year because of air pollution. The number is growing: admissions for respiratory ailments at a busy teaching hospital soared fourfold between 2008 and 2015 according to an investigation by the Indian Express, a newspaper. And the trouble is not confined to the capital. In the country as a whole the number of early deaths caused by toxic air could exceed 600,000 a year. The largest cause is not cars or factories: it is smoke from home cooking, while in northern India stubble-burning in the countryside is also a factor. But vehicles play a big part, and it is to this source that the keenest attention is now being paid.

Ashes to Ashes

On January 15th Delhi wrapped up a drastic two-week experiment to reduce car emissions by restricting road use to odd- or even-numbered licence plates on alternate days (a method occasionally used in Beijing, São Paulo and a dozen other cities). When the local government announced the scheme in December, many predicted failure. Proud car-owners would ignore it. Police would be too few or too corrupt to enforce compliance. And anyway, in a city with 2.9m cars but some 7m motorbikes and motorised rickshaws, and with many exempt from the ban such as taxis and other public vehicles, the effects would be minimal.

Yet it seems to have been a striking success. With teams of volunteers manning corners to shame would-be shirkers into parking their cars, and police out in force to slap on fines, few flouted the ban. Nor can anyone now claim to be unaware of a problem to which residents had become so inured that it has hardly featured in elections to date. Public transport was more crowded, but passengers were delighted to find traffic markedly lighter.

True, by the measure of the nastiest element in Delhi’s toxic cocktail, ultrafine particles, the drop in emissions was not drastic. The first days of the new year even saw a discouraging spike in concentrations of PM10 and PM2.5, as the diameter of two sizes of particles are commonly defined in thousandths of a millimetre. In parts of the city, PM2.5 (the more harmful of the two sorts, because it penetrates the lungs more deeply) exceeded 500 micrograms per cubic metre. That is 20 times the WHO’s guideline for safe air.

Still, notes Anumita Roychowdhury of the Centre for Science and Environment, a think-tank in Delhi, those highs were largely due to winter weather, and were lower and shorter-lasting than previous peaks. The odd-even test not only showed that such emergency measures can limit dangerous pollution; it showed how much more efficient public transport can be when road space is freed up to let it move.

The positive response has jolted politicians and India’s courts into action. In December the country’s Supreme Court slapped a citywide ban on the registration of luxury diesel cars. Soon afterwards, the national government declared that it would speed up the introduction of stricter emissions standards for new passenger cars. It is now considering a similar move for two- and three-wheelers. The government is also hurrying to improve the quality of fuel.

If both new sets of regulations come into effect by 2020, as is planned, new vehicles will emit only a fraction of the pollution they do today. Other initiatives include the expansion of Delhi’s metro, measures to maintain roads better (the dust kicked up from these accounts for a big proportion of breathable particulates), restrictions on lorries entering the city, and plans to enforce the replacement or retrofitting of older vehicles. If all this is done, Delhi may get acceptable air in a few years’ time.

It is not the first time the central government has acted against air pollution. Over a decade ago it introduced a battery of pollution controls, such as requiring most buses, taxis and auto-rickshaws to convert to natural gas. It banned the burning of rubbish and shut down heavily polluting industries as well as power plants. Those measures worked too, getting rid of the coarsest grit. People noticed that their shirt collars were no longer dirty, says Sumit Sharma of Delhi’s The Energy and Resources Institute, another NGO. “They thought the problem was solved.”

Wild is the Wind

Two things then intervened to undermine progress. One was a tripling of the number of vehicles on India’s roads between 2002 and 2013. The other was misguided government policy. By subsidising diesel in a bid to woo farmers who rely on it to power water pumps and tractors, successive governments encouraged a massive shift in Indian vehicle markets. Between 2000 and 2013 the proportion of new cars with diesel engines rose steeply, from one in 20 to one in two.

California’s environmental regulatory agency—the body that recently exposed cheating on diesel emissions tests by the German car firm Volkswagen—says diesel exhaust poses the highest cancer risk of any toxic air contaminant it has evaluated. Luckily, the Indian government’s mistake has already been corrected. In October 2014 it scrapped diesel subsidies; sales of diesel vehicles have already dropped. This month a supreme-court judge had this to say to lawyers from a carmaker who argued against the ban on diesel-guzzlers: “So are your vehicles emitting oxygen?” The horrors of Delhi’s air are sinking in.