The Environmental Protection Agency on Thursday set a new health standard that coal-fired power plants and other industries will have to meet on sulfur dioxide, a pollutant that triggers asthma attacks and causes other respiratory problems.

The EPA set the new standard within a range that an independent panel of scientists suggested. This marks the first time the standard has been changed since the original one was issued in 1971.

The new rule sets the amount at 75 parts per billion over a one-hour period, a level that's aimed at protecting people who go outdoors from short-term exposures. The EPA said that even brief exposure could create health problems, especially for children, people with asthma and older people.

Data released on Thursday has shown that the US economy is continuing to grow, with both factory output and the services sector still expanding.

US factory orders increased 1.2% in April, said the Commerce Department, led by a big rise in orders for commercial aircraft.

The Institute of Supply Management said service industries grew in May for the fifth month in a row.

US economists are now awaiting Friday's release of May's unemployment data.

This is expected to show that while the US economy added about 500,000 jobs last month, unemployment remained at just under 10%.

The reason for this apparent contradiction is that more people are starting to look for work as the economy continues to recover, thereby boosting the size of the overall labour force.