Sitting at a desk in his small office here, Ma Jun, one of China’s best-known environmental advocates, shows off his latest tool in the fight against the nation’s crippling air pollution- a computer app.Displayed on a tablet, the app shows a map of northeastern China covered with large orange circles, each representing one of the country’s major polluters, reporting its emissions in real time.The data come from automated monitoring equipment the government has installed at about 10,000 plants around the country. Ma and his colleagues at the Institute of Public and Environmental Affairs, a Beijing-based environmental group, have made that information available to millions of Chinese on their own computers and mobile devices.The app is part of an ambitious effort by environmentalists to use data and social media to use the power of public opinion in a country that lacks other routes to social change, such as elections or an independent judiciary.China has many laws against pollution, Ma said, but “enforcement is weak” because the cost of committing violations is too low.Many of the worst polluters are state-owned companies or have close ties to regional officials. Among the worst offenders are companies such as Tianjin Pipe Group, China’s largest producer of crude-oil pipelines, which recently ranked as the region’s top source of airborne particulates, and the Dezhou Kaiyuan power plant in Shandong province, southeast of Beijing, which topped the list for sulfur dioxide, emitting seven times the limit.Especially at the local and provincial level, officials suffer from a “lack of motivation” to pursue serious polluters, Ma said. Public “transparency is one of the very few options we have” to “drive enforcement,” he said.Over the past several months, the app has been downloaded about 10,000 times.Whether making data about emissions accessible to the public will be enough to overcome entrenched resistance to pollution cleanup remains to be seen. But the stakes could hardly be higher.A study published last year by the U.S. National Academy of Sciences indicated that air pollution, primarily from coal burned for heat and electricity, reduces the average life span of the 500 million residents of northern China by 5 1/2 years, compared with those living in the somewhat less polluted southern part of the country where the government does not supply steam heat in the winter.A separate study conducted by researchers at Tsinghua and Peking universities and released last month by the New York-based Natural Resources Defense Council estimated that in 2012, coal burning led to 670,000 premature deaths in China from diseases such as heart disease, stroke, emphysema and lung cancer. As far away as California, emissions blowing across the Pacific from China on some days account for up to a quarter of airborne pollutants such as sulfur compounds, according to U.S. pollution data.Moreover, the same smokestack plumes that blanket China’s cities in stifling clouds of tiny, lung-scarring particles make the country the world’s leading contributor to global warming.Chinese President Xi Jinping struck an agreement with President Barack Obama under which China pledged to cap its emissions of carbon dioxide, which scientists say is the major contributor to global warming, within 15 years. It also promised to boost its use of renewable fuels to one-fifth of the nation’s power consumption by 2030.Meeting that goal and improving the health of China’s population require grappling with the country’s huge reliance on coal. Other factors, including cars, construction dust and burning of waste, contribute to pollution, but coal, which provides about 70 percent of China’s energy, accounts for 50 percent to 60 percent of the fine particulates in its air and most of its carbon emissions, said Alvin Lin, energy policy director at the NRDC’s Beijing office.Officially, China has embraced the goal of reducing that pollution. This year, Premier Li Keqiang vowed a “war on pollution” as part of China’s efforts to upgrade its economy.After years of trying to suppress information about pollution, the government in recent years increasingly has admitted its extent. Until 2012, for example, no cities in China were allowed to publicly disclose the level of so-called PM2.5, the tiny particles that cause the most damage to human lungs, Ma said. Now 190 cities do.State-controlled news media report extensively on air quality, although the government still sometimes blocks access to data from the air quality monitoring station on the roof of the U.S. Embassy here.A cleanup on the scale of what China needs, however, will be hugely expensive and time-consuming. To reduce its reliance on coal-generated electricity, for example, China plans to build nearly 60 new nuclear power stations, up from 23 currently, with 26 of them already under construction, according to the International Atomic Energy Agency. The country also will increase its imports of natural gas and greatly expand its use of solar and wind power over the next couple of decades, officials say.Senior Chinese economic officials say the country also will have to close down its oldest, dirtiest and least efficient heavy-industrial facilities, such as steel mills and cement factories, where China has far more production capacity than it needs.Many of those moves run up against powerful, entrenched interests. Local and regional officials are still judged mostly on their ability to hit economic growth targets, although the central government has moved to start adding environmental goals to their evaluations. State-owned firms, such as Sinopec, the huge oil and gas company, have strong influence over government policy.Officials, however, also have compelling reasons to back a cleanup, including fears of domestic unrest and worries over the mounting costs of pollution.As recently as five years ago, the environment ranked relatively low among public concerns. But now, pollution routinely is among the top issues the Chinese worry about, along with jobs, retirement security and education, said Victor Yuan, whose company, Horizon, runs China’s largest polling operation.Translating that general concern into specific pressure for cleaning the air is where Ma’s pollution map comes in.If the public understands exactly where the pollution is coming from, “it becomes risky for governors and mayors to interfere,” Ma said. He and his colleagues have seen progress. Since they began publicizing factory emission levels, about 200 major polluters have contacted them to discuss their cleanup plans, he said.Even in the best of circumstances, cleaning China’s air to the level of international health standards would take decades, much as it has in the U.S., Ma acknowledged. But, he said, a relatively small number of plants contribute outsize amounts to China’s pollution, and targeting them can bring about significant improvements much sooner.Ma cites the blue skies at November’s Asia-Pacific economic summit in Beijing as proof of what can be achieved. The Chinese government took extraordinary steps to clear the air, including shutting down polluting factories across the region and giving government workers days off to reduce traffic. The results showed “you don’t need 30 years” to clear the air, Ma said, just the motivation to tackle the job.After years of pursuing “development at any cost,” China has hit “some sort of watershed moment” when public unhappiness over pollution reached a level that the government cannot afford to ignore, Ma said. “The smog issue finally has created some real political will” for change.Times staff writer Julie Makinen and Tommy Yang in The Times Beijing bureau contributed to this report.