A new study has cast doubts about whether air quality has truly improved in Beijing and has concluded that "irregularities" in the city’s system of measuring air pollution have enabled the city to meet environmental targets linked to the coming Olympic Games.
The study, written by an American environmental consultant, found flaws in Beijing’s "Blue Sky" system of air quality monitoring stations and noted that the city changed its method for measuring pollution in 2006. In particular, officials stopped including readings from two stations in polluted areas and began using readings in three other stations in less polluted locales.
Without this switch, Beijing would have fallen far short of its goals in 2006 and 2007 for the number of days that met national air quality standards, according to the study. The study also found that a disproportionate number of days were rated just below the statistical break point that separates a polluted day from one that passes standards.
"Irregularities in the monitoring of air quality account for all reported improvements over the last nine years," said Steven Q. Andrews, the author of the study, in a telephone interview. Mr. Andrews published an op-ed article about his study on Wednesday in the Asian edition of The Wall Street Journal.
On Wednesday afternoon, Du Shaozhong, deputy director of Beijing’s Environmental Protection Bureau, reviewed a faxed copy of the article but responded in broad terms rather than addressing any specific findings. He agreed that Beijing still needed to make progress in reducing air pollution but said the city’s air had undeniably improved.
"Over the past 10 years, through our enormous hard work, Beijing’s air pollution has visibly improved," Mr. Du said in a statement. "This is an indisputable fact."
He added, "We have patience for that small group of people who don’t understand, and we believe that, as time passes, and in the face of facts, they will eventually understand."
Mr. Andrews said he based his study, which has not undergone peer review, on official government statistics. He spent more than a year in Beijing as a Princeton in Asia fellow at the National Resources Defense Council, or N.R.D.C., a nonprofit environmental group. But he said his study was independent of his association with the council.
With roughly seven months remaining before Beijing plays host to the Olympics, air quality has become a major concern. Chinese officials have pledged that pollution will not be a problem during the Olympics and are discussing contingency plans that include possible factory shutdowns or traffic restrictions, if necessary.
But Beijing officials also have pointed to improved Blue Sky air quality ratings as proof that the city is fulfilling its commitment to clean itself up for the Olympics. The Blue Sky program, used in 84 major cities across China, measures sulfur dioxide, nitrogen dioxide and airborne particulate matter known as PM10.
Pollutants are measured on a scale of 1 to 500, with 500 considered the worst score. Any rating below 101 meets national air quality standards and is considered a "Blue Sky day." The city’s overall daily rating is determined by whichever of the three pollutants has the highest rating for a 24-hour period. In Beijing, PM10 is almost always the worst pollutant.
In 1998, Beijing recorded only 100 Blue Sky days. In 2007, that number had risen to 246, a fact hailed last week in China’s state media.
But Mr. Andrews said the recent improvement was largely the result of changing the formula in 2006. He said the city’s daily pollution rating was based on readings from a subset of the more than two dozen monitoring stations around the city. Mr. Andrews said readings from seven stations were used from 1998 to 2005.
But in 2006, the city dropped two stations located near areas with high traffic and replaced them with three other stations in quieter areas. The impact on the Blue Sky ratings was drastic; Mr. Andrews found that using the original seven stations would have meant 38 fewer Blue Sky days in 2006, and 55 fewer last year.
This would have meant that Beijing had fewer days meeting national air quality standards last year than in 2002, when there were 203.
Mr. Andrews also found that ratings began to change after officials set targets for every monitoring station in the city. He said this political imperative coincided with a rising number of days that rated just below the break point of 101 to qualify as a Blue Sky day.