The Obama administration on Friday issued a proposed rule governing hydraulic fracturing for oil and gas on public lands that will for the first time require disclosure of the chemicals used in the process.

But in a significant concession to the oil industry, companies will have to reveal the composition of fluids only after they have completed drilling — a sharp change from the government’s original proposal, which would have required disclosure of the chemicals 30 days before a well could be started.

Oil and gas companies will have to capture toxic and climate-altering gases from wells, storage sites and pipelines under new air quality standards issued on Wednesday by the Environmental Protection Agency.

The rule is the first federal effort to address serious air pollution associated with the natural gas drilling process known as hydraulic fracturing, or fracking, which releases toxic and cancer-causing chemicals like benzene and hexane, as well as methane, a powerful greenhouse gas.

The Environmental Protection Agency has postponed its first rules aimed at reducing air pollution from natural-gas wells that are drilled by hydraulic fracturing, following a last-minute push by oil and natural-gas companies to weigh in on the new standards.

The EPA said in a statement Monday it was postponing the rules by two weeks, pushing back a deadline until April 17. The agency said it needed more time to digest more than 150,000 comments that had been submitted on the rule.

Hong Kong has decided to come clean with data on a dangerous form of air pollution, a month and a half after Beijing, a city with smoggier skies and a murkier approach to statistics, did the same.

After years of withholding the data, Hong Kong’s environmental protection department on Thursday began publicly releasing hourly measurements of the tiny pollutants known as PM2.5 – so called because they are smaller than 2.5 micrometers in diameter – that health experts say are especially threatening because they penetrate deeply into the lungs.

There's new evidence that exposure to exhaust from diesel engines increases the risk of lung cancer.

Diesel exhaust has long been classified as a probable carcinogen. But the 20-year study from the National Cancer Institute took a closer look by tracking more than 12,000 workers in certain kinds of mines — facilities that mined for potash, lime and other nonmetals. They breathed varying levels of exhaust from diesel-powered equipment, levels higher than the general population encounters.

China said Friday that two-thirds of its cities currently fail to meet new air-quality standards introduced this week that are based on the pollutants most harmful to health.
Under pressure from a worried Chinese public, the government this week issued revised air-quality targets based on the smallest particulates, which make up much of the country’s air pollution.
Cities will have four years to get their pollution levels down to the new limits, which cover levels of ozone and particulates measuring 2.5 micrometres or less, known as PM 2.5.

China’s cabinet ordered on Wednesday new air-quality standards to measure the most dangerous form of particulate matter, following a public outcry over worsening air pollution.
The State Council told 31 major regional capitals including Beijing and Shanghai to begin monitoring PM2.5 particulate, or fine particles measuring 2.5 microns in diameter, this year, the cabinet said on its website.
The new measure — which had been demanded by environmental campaigners — would be compulsory for 113 more cities in 2013, it said.