Away from the flames, millions of Australians are breathing unhealthy air this summer as smoke from the country’s disastrous wildfires clouds skies from Sydney to Canberra to Melbourne. Australia’s capital, Canberra, has been blanketed by a thick haze of smoke from nearby fires for more than a week. The city recorded its worst air quality day on Jan. 2, with readings of dangerous fine particulate pollution spiking to over 200 micrograms per cubic meter on average during the worst hour, according to Berkeley Earth, a nonprofit research group that aggregates data from air-quality monitoring sites. Readings for the day averaged nearly 100 micrograms per cubic meter, a level considered “unhealthy” under air quality standards developed by the United States Environmental Protection Agency.

Normally, air pollution in the city is low. Southeastern Australia is experiencing one of the worst fire seasons on record, with hundreds of fires burning across the states of New South Wales and Victoria. Fires have seared millions of acres since October, destroying more than a thousand homes and killing at least 19 people, including three volunteer firefighters.

Wildfires release air pollutants like carbon monoxide and nitrous oxide, which can harm the health of residents nearby and firefighters on the front lines. Another byproduct of burning, fine particulate pollution known as PM2.5 because particles measure less than 2.5 micrometers across, can be transported long distances.Breathing in these tiny particles can worsen asthma and other respiratory disorders, and lead to heart attack and stroke, among a slew of other health effects. High levels of PM2.5 pollution are particularly harmful to older people, the very young and people with compromised immune systems.

An elderly woman is reported to have died on Thursday after going into respiratory distress when she got off a plane at the Canberra airport.