Virginia DEQ has issued an air quality health alert for the region that includes the City of Danville and Pittsylvania County.
Those with health conditions as well as all children and elderly people should avoid outdoor activity.
Of Virginia's 24 DEQ regions, the Roanoke region has the highest overall threat.
The air pollution is the result of numerous large wildfires burning in the Canadian plains and in the western U.S.
Air pollution levels are expected to stay moderate to high in Central and Southside Virginia until late Friday, when they are expected to return to mild.
Particle pollution is made up of particles found in soot, dust, smoke and fumes. The burning of coal, oil, diesel and other fuels produces these particles. The particles are small enough to enter deep into the lungs and cause health problems.
Ozone and particle pollution have been linked to short-term health concerns, particularly among children, asthmatics, people with heart or lung disease and older adults.
The effects of these pollutants can be minimized by avoiding strenuous activity or exercise when levels are high.
Pollution particles enhance sunrises and sunsets, which gives the sun and moon a bright red glow.