New Delhi's air has already been ranked as the world's most polluted. But as researcher Joshua Apte tells DW, a new study has yielded some alarming results for anyone living near or alongside roads in the Indian capital.
Following a study published this year of 1,600 cities across the globe, the World Health Organization (WHO) found that New Delhi had the world's highest annual average concentration of small airborne particles - higher than major Chinese cities. The tiny floating particles, measuring 2.5 micrometres or less in diameter, are hazardous because they can penetrate deeply into the lungs and cause respiratory and cardiovascular diseases.
While Delhi authorities have disputed the WHO's findings, India's environment court, the National Green Tribunal, recently slammed the government over the capital's air pollution levels, directing all vehicles older than 15 years be taken off the city's roads and ordering that pollution checks be undertaken for all state-run buses and that air purifiers be installed at the city's busy markets.
While environmentalists welcomed the court's ruling, a study conducted by researcher Joshua Apte and his partners at the University of California, Berkeley, and the Indian Institute of Technology in New Delhi suggests this might not be enough. Roaming the Indian capital's streets in a autorickshaw fitted with air pollution monitors, the researchers found that average pollution levels were up to eight times higher on city roads. Air quality is represented by the annual mean concentration of fine particulate matter: PM10 and PM2.5, referring to particles smaller than 10 or 2.5 microns.
In a DW interview, Apte says the high pollution levels in Delhi come from a wide variety of sources, with no single dominant emissions source. As with many other places in the world, transportation is an important source, accounting for roughly 30 percent of the total PM2.5 emissions within the Indian capital.
DW: How would your describe the issue of air pollution in India's capital New Delhi?
Air pollution is a large and growing health concern in New Delhi and throughout India. In terms of health risks, the most important pollutant is thought to be PM2.5 - fine particulate matter - which has a strong association with premature death from heart attacks, stroke, lung cancer, and other diseases. Roughly 630,000 Indians die each year from diseases related to outdoor air pollution, more than three times as many as AIDS and malaria combined.
Over the course of a year, urban background - ambient - pollution levels in Delhi are among the highest levels measured in the world. However, official air quality monitors miss one important aspect of the air pollution that ordinary citizens experience. In Indian cities - and in many other countries, including the USA -, PM2.5 is measured at a small number of background sites that tend to be located away from major sources such as traffic. These monitors do not reflect elevated levels of pollution that people are exposed to on the road.
Our study took a detailed look at one aspect of air pollution - the very high levels that one frequently encounters in traffic. We found that the exposures that one experiences on and near roads can substantially exceed what one would measure at an official monitoring site.
What are the main contributing factors to this development?
Delhi has high urban background levels of PM2.5, with annual average concentrations roughly 15-20x higher than WHO's recommended guideline: annual average concentration of 10 µg per cubic meter.
PM2.5 in Delhi comes from a wide variety of sources, with no single dominant emissions source. As with many other places in the world, transportation is an important source, accounting for very roughly 30 percent of total PM2.5 emissions within Delhi. Industrial pollution is an important source in some parts of Delhi, including less-regulated informal industries such as brick manufacturing located just outside of the city.
Other distributed local sources include burning of wood and waste, diesel backup generators, and construction. Finally, the wind brings in air pollution from outside Delhi - from electricity generation, burning of crop wastes, and other sources - contributing to the high levels.
Did your measurements/readings differ from those obtained by the city's official air quality monitors?
In our study we wanted to compare levels of air pollution in New Delhi traffic with the urban background that one typically reads about. We spent 4 months making detailed measurements of three types of particulate matter inside auto-rickshaws and cars in rush hour traffic. Simultaneously, we made continuous measurements of urban background pollution in a clean, high-income Delhi neighborhood.
As one would expect, average pollution levels on the road were much higher - depending on the type of PM, anywhere from 50 percent to 8 times higher than the urban background. The levels of in-vehicle pollution measured rank among the very highest levels routinely measured in a transportation setting anywhere in the world.
Our findings suggest that time spent in traffic represents an additional major source of pollution exposure that is not fully accounted for in the official measurements. In addition to the 2-3 hours that many people spend in Delhi traffic, one must consider the large number of people who live near major roads, or spend their lives working in and on the streets. For example, many auto-rickshaw drivers routinely work 10 hours or longer each day.
Delhi authorities have disputed a recent WHO report that the city has the world's highest annual average concentration of small airborne particles. Does your study confirm the WHO's findings or is it even worse?
In my opinion, this discussion is really beside the point. This is, of course, a contest where no-one wins. No matter where New Delhi falls in this ranking, there is ample evidence that pollution levels in Delhi are far higher than a safe level of exposure.
Annual average concentrations of 150 µg per cubic meter substantially exceed what the WHO, the US EPA, and the Indian government consider to be a safe level of PM2.5 exposure - respectively 10, 12, and 40 µg per m3. The crucial discussion here ought to lie around strategies for promptly and substantially reducing levels of air pollution in Delhi.
As an aside, there are of course pitfalls in this type of ranking. First, Delhi has one of the most extensive air quality monitoring networks of any Indian city - but levels may well be higher in other cities with less data available. Second, as our study shows, pollution levels in a city vary sharply in space and time - and some parts of Delhi are of course more polluted than others.
What I meant to ask was: what were the highest pollution levels you measured?
We conducted our study during morning and evening rush hour traffic over four months that represent a range of winter and summer conditions (February - May). Overall ambient pollution levels were highest in the winter period (February). In-vehicle levels were consistently high throughout the entire study period, but of course, varied widely over short periods of time as we moved through traffic.
For example, a brief encounter with the exhaust plume of high-emitting vehicles is shown in this YouTube video. Short-duration peak in-vehicle levels of pollution on each trip were between 3 and 20 times higher than the ambient concentrations in Delhi. While we don't know enough to say what the health risks of these intense bursts of pollution might be, they are short enough in duration that holding one's breath could be enough to somewhat avoid them.
How dangerous has the situation become for public health in the capital?
The very high levels of pollution in Delhi do raise important health concerns - especially for the young, old, and vulnerable. Winter in Delhi brings episodes of severe pollution, with daily average levels exceeding 300 µg/m3 and hourly levels sometimes topping 600 µg/m3. One hears news reports of spikes in hospital admissions for respiratory and cardiac conditions during these times.
Because comprehensive archival data on pollution in Delhi are not readily available to the scientific community at large, it's hard to draw a complete picture about how pollution levels are shifting in Delhi. From the data I have seen, however, it's quite clear that the situation has not improved much, if at all, over the past several years.
What must the people of Delhi and the Indian government do to tackle this issue?
This is the area of the problem that gives me the greatest hope. There are numerous low-hanging fruits that can help put Delhi on a path towards much cleaner air - and plenty of opportunity for India to display its engineering and scientific prowess in addressing air quality.
Some key approaches to cleaner air in Delhi include tightening vehicle emissions standards to world-class levels, adopting cleaner fuels in passenger vehicles (CNG, low-sulfur diesel), phasing out older vehicles, cleaning up the high emitting trucks that ply Delhi's roads at night, reducing urban burning of wood and wastes, reducing emissions from diesel backup generators, and cleaning up rural industries such as brick kilns.
There is also a tremendous opportunity to leapfrog more polluting paths of development, whenever possible. For example, solar electricity is now price competitive with imported coal power in the Indian market. There are numerous examples of these win-win scenarios that save money, reduce pollution, and save lives. And of course, India has the talent to innovate new approaches to reducing pollution that can be an inspiration to the rest of the world.
Joshua Apte is an ITRI-Rosenfeld Postdoctoral Fellow at Lawrence Berkeley National Laboratory, and also an Assistant Professor at the University of Texas at Austin.