For the second time in less than a year, a state air monitor has recorded high levels of dangerous air pollutant near the Northern Metal Recycling shredder in north Minneapolis, the Minnesota Pollution Control Agency reported.

The state environmental agency cannot pinpoint what's causing the recent pollution spike, other than perhaps the warmer weather might play a role. Last year, Northern Metals agreed to shut down its shredder in the area and relocate in 2019, after years of air pollution problems and pressure from neighbors.

On April 24, the agency's air monitor located just south of the Lowry Bridge on the west bank of the Mississippi River recorded a 24-hour average of 161 micrograms per cubic meter of airborne particulates called PM10, exceeding the federal standard of 150.

Hourly recordings on the same day showed levels that were as high as 500 micrograms per cubic meter, according to Frank Kohlasch, manager of the MPCA's air assessment section.

"We are very concerned about the impact ... on people working and living near that industrial part in Minneapolis," Kohlasch said.

Deemed harmful to human health, the pollutant has been linked to aggravated asthma, respiratory problems and premature death.

The MPCA air monitor had recorded high levels of the particulate at the same location two other times since the monitoring started in 2014.

In an e-mail to constituents Thursday, Rep. Diane Loeffler, DFL-Minneapolis, raised concerns about health risks posed by the air pollution.

"We need to reduce the level of fine particulates in our area and it's my hope that the city's comprehensive plan, now in development, will exclude new businesses that might contribute to this in areas already identified as being overburdened," Loeffler said.

The MPCA and the city of Minneapolis have been coordinating efforts to step up street sweeping and other activities to reduce pollution in the industrial zone.

"This particulate is a serious matter. We take it very seriously and we are trying to stay ahead of the problem," said Jim Doten, Minneapolis supervisor of environmental services.

In recent years, the MPCA has sought to reach voluntary agreements with industrial facilities in north Minneapolis aimed at reducing air particulate matter that may contribute to pollution. So far, six companies have signed the agreement; the agency is working with three other companies to sign, said Sarah Kilgriff, MPCA's manager of the land and air compliance section.

In March 2017, Northern Metal Recycling reached a settlement with the MPCA to pay $2.5 million in costs and penalties, and to relocate the recycling plant from Minneapolis to Becker by August 2019. Nearly 25 percent of the settlement money was appropriated for asthma and lead-poisoning mitigation in neighborhoods surrounding its north Minneapolis plant.

The settlement was one of the largest the MPCA has ever negotiated.

"Just because Northern Metals is moving doesn't mean that we still don't have significant work to do in that area because that area is a heavy industrial area," Kilgriff said.

If particulate levels continue to violate the federal standard, the state agency may take additional enforcement and the U.S. Environmental Protection Agency may step in.

Mukhtar M. Ibrahim • 612-673-4689 Twitter: @mukhtaryare