HARRISBURG — Pennsylvania environmental regulators say a four-week study of air quality near natural gas drilling operations failed to turn up harmful emissions levels.

The Department of Environmental Protection said today its assessment focused on volatile organic compounds typically found in petroleum products, as well as other pollutants near drilling sites in Susquehanna and Sullivan counties.

DEP says its testing revealed the main constituents of natural gas and related compounds, but none at concentrations that would trigger health problems.

The agency has received odor complaints from residents downwind of extraction and processing sites.