Our summer started not with sunshine but with smoke last week, causing the most widespread hazardous air quality seen in years across the eastern US.
Together with our partners at the North Carolina Department of Air Quality (NC DAQ) who are responsible for providing air quality forecasts for the state, we are taking a closer look at the event. and its impact on our atmosphere in NC.
Origin of smoke
ONE anomalous ridge of high pressure built across Canada this spring, allowing record-breaking hot and dry conditions to prevail across the country. Towards the end of May, a combination of unseasonably warm weather the temperature reaches the 90s and dry weather throughout Quebec created ideal conditions for forest fire grows.
As the thunderstorm moves through, lightning strikes ignite more fires. In total, more than 150 wildfires in the province burned nearly 400,000 acres in the first week of June.
In North Carolina, we enjoyed relative the weather has been cooler in the past monthbut ironically, the overall weather pattern behind those pleasant conditions eventually pushed the smoke in our direction.
North-northwesterly winds around a fixed depression upper level low pressure system off the Northeast coast blew the smoke south in the middle of last week. On its way to North Carolina, it created Code Purple air quality across the mid-Atlantic – complete with a spooky orange fog – on Wednesday, June 7.
Our own air quality problems began on Tuesday, June 6 as a cold face pushed in from the north, carrying the smoke and trapping it close to the ground beneath a dense layer of clouds, sent pollutant concentration increases.
Our north anchored upper-level low-pressure system provided a continuous stream of smoke-filled air directly from Canada into our region. As that lower upper layer slowly receded north and east over the weekend, smoke transport ended and particulate pollution levels gradually lowered.
This same type of setup was responsible for another recent episode of poor air quality in July 2021as smoke from central Canada moved in, rapidly increasing hourly pollution levels across much of the state.
Observation conditions
The main concern during last week’s smoke event was fine particulate matter: effectively, small bits of burned trees and ash were carried by the wind from fires spreading across eastern Canada, including Quebec and Nova Scotia.
This type of pollution is classified as PM2.5, or particulate matter less than 2.5 micrometers in diameter – only a fraction of the width of a human hair. Due to their small size, these particles can be easily inhaled and cause respiratory problemsalong with eye, nose and throat irritation.
The EPA standard for assessing PM2.5 levels is average daily concentration — that is, the 24-hour average from midnight to midnight — as measured by the statewide network of official NC DAQ monitoring stations. NC DAQ forecasters are predicting this daily average with air quality forecast for PM2.5.
In addition, this concentration serves as the basis for the color coding Classification of air quality indexreflect the health effects of long-term exposure.
A mean daily concentration of at least 35.5 micrograms per cubic meter equivalent to Code Orange, or Unhealthy for sensitive groups such as children, the elderly and people with heart and lung diseases. And when the average daily concentration exceeds 55.5 micrograms per cubic meter, that’s the Code Red range, or Unhealthy for everyone.
The first signs of worsening air quality during the event appeared on Tuesday across the Triad. That afternoon, PM2.5 concentrations were observed at the Hattie Avenue display in Winston-Salem add to 76.2 micrograms per cubic meter – definitely within the Code Red range, if concentrations stay that high throughout the day. The daily average for both NC DAQ Forsyth County monitors ends at Orange code level.
For Wednesday, NC DAQ forecast common Code Red conditions through Piedmont and the Northern Mountains. On that day, supervisors in Montgomery and Wake counties registered maximum concentration in 1 hour within that range, although fine particle concentrations decreased later in the day, leaving most areas with Daily average yellow code.
Raleigh’s Millbrook Monitor recorded average daily PM2.5 concentrations in the Orange Code range on both Thursday And Friday. This is the first multi-day Code Orange PM2.5 event for the Triangle since November 18-19 2016, when smoke from Appalachian forest fire spread across the state.
Most states experience Code Gold AQI levels or worse Tuesday through Sunday. That was accompanied by elevated ozone levels along with cloudy skies combined with a lingering smoky air mass, visible above. satellite images and can even be detected by our ECONet. On Tuesday night, our station in Greensboro measured solar irradiance values up to 40% lower than expected on another clear day at this time of year.
A rare air quality event
North Carolina saw Significantly improved air quality, largely due to vehicle and power plant emissions regulations that have cleaned the air locally. In recent years, it has brought specific atmosphere setting or large wildfires that cause serious and/or persistent air quality concerns.
However, some parts of the state have have seen air quality decline this year from sources closer to home. This spring, a fire burning in our relative’s backyard is also causing the intervals low visibility, Depleted air qualityand even ashes fall from the sky in eastern North Carolina. The Great Lake Fire caught fire in the Croatan National Forest on April 19 and created a plume of smoke that affected areas from New Bern to the north.
During that short-lived smoke event before weekend rains helped put out the fires, NC DAQ monitors in Northampton County and Pitt County measured 1-hour maximum PM2.5 concentrations. ninety four And 127 micrograms per cubic meter respectively. Both are in the Code Red range, although their average daily concentrations are only Code Yellow. Sites closer to the fire may have experienced Code Red or worse conditions.
Code Red AQI Days are rare in North Carolina. The last time average daily PM2.5 concentrations reached or exceeded that particulate contamination level over a large area of the state was during the November 2016 Western Wildfires in California. Charlotte and more western North Carolina.
In eastern North Carolina, the last or worse Code Red event – before the Great Lake Fire – due to PM2.5 levels is likely to occur in June 2011, as smoke from the Bay of Pains fire burning along our coast pushed inland. Finally, many regions also have Code Red ozone concentration above June 29, 2012associated with a hot, polluted air mass moving in from the west.
While air quality conditions improve daily, this spring and early summer have reminded us that under the right conditions – including the fires burning in our state, or more than a thousand miles away – unhealthy air quality is still possible in North Carolina.
