Before we read too much into the NYT Journalist's article, here is another view:

For an article that talks in excruciating detail of the cataclysmic effect Delhi’s air has had on the health of the author’s child—and the ethical dilemma faced by expats, whether they should risk raising their loved ones in this godforsaken metropolis—for all those morbid adjectives and gut-wrenching, bile-inducing descriptions, Harris quotes but a single scientific study.

“Delhi, we discovered,” he writes, “is quietly suffering from a dire paediatric respiratory crisis, with a recent study showing that nearly half of the city’s 4.4 million schoolchildren have irreversible lung damage from the poisonous air.”

Single it may be, a citation is still a citation. Except that here it is in the form of an article written in The Indian Express, and worse, the study it quotes is born out of data that was collected between 2002 and 2005. Yes, more than 10 years ago.
Discounting the fact that Harris insists on calling it “a recent study”; discounting also the fact that The Indian Express blunders with their subheading—“Just under half of the 44 lakh schoolchildren studied…” it says, while in reality only 11,628 schoolchildren were studied and the results of the survey extrapolated—the cited report is as comprehensive as one can get.

The study points to the harmful effect Delhi’s air had on the health of 11,628 schoolchildren between 2002-2005: “In lung tests conducted on 5,718 students, 43.5% suffered from “poor or restrictive lungs”; about 15% of the children surveyed complained of frequent eye irritation, 27.4% of frequent headache, 11.2% of nausea, 7.2% of palpitation and 12.9% of fatigue.”
But it is more nuanced than that. The study surveyed children from 36 schools, six of which were situated on Delhi’s main roads that are notoriously choked with traffic all through the day, with one, Lakshmi Public School—that presented one-tenth of the children surveyed—located near one of Delhi’s biggest bottlenecks: Vikas Marg intersection. It is also worth noting that in 2002, neither Delhi’s fleet of 6,000 rickety diesel buses had been phased out despite Supreme Court orders, nor had most of the 25,000 odd auto rickshaws converted to compressed natural gas, or CNG.
In the age group of six to eight—the same as Harris’ son—the prevalence of current asthma in Delhi’s children was found to be marginally higher: 2.5% compared to 2% in the control group. Prevalence of current asthma shot up in children belonging to large-sized families and families with poor socioeconomic background (5.1% for a family size greater than six).

The study found a strong positive association between PM10 and eye irritation, but not with asthma or headache. (PM10, or Particulate Matter of size 10 microns, and PM2.5, or Particulate Matter with size equal to or less than 2.5 microns, are the two major determinants of air pollution. It is now an accepted scientific fact that prevalence of PM2.5—measured in µg/m3—is more dangerous than PM10 as it settles deep inside the lungs).
About 27% of Delhi’s children studied were exposed to cigarette smoke at home (control 28%) and, crucially, the study found that a child’s BMI, or body mass index, has a profound influence on his lung function.

http://qz.com/420275/about-that-new-york-times-story-on-delh...