That feeling of spring in the air will soon combine with pollen grains, some smoke, and potentially even dangerous pollutants as the weather continues to warm.
March not only marks the beginning of meteorological spring, but also the beginning of the ozone season, which lasts from March 1 to October 31. As we all know. discussed beforeNorth Carolina Department of Air Quality (NC DAQ) released daily Air Quality Index forecast during the ozone season for ground-level ozone, which can cause adverse health effects at high, out-of-the-year concentrations for fine particulate matter.
Air quality assessment in 2021
Last year, North Carolina continued to enjoy clean air quality most days. During the 2021 ozone season, there are only two days (May 24 and July 30) that any monitoring device in the state measures daily ozone concentrations that exceed the standard set by the EPA for clean air quality.
Another two days (4th of july and July 21) has an impact on air quality from fine particles caused by smoke from very different origins, such as discussed in a previous post introduced our newest air quality tool, Person reporting ambient information.
Most notably, smoke from wildfires in the western United States and central Canada was carried by upper-level winds into North Carolina in late July. That largely reflects the recent evolution of our air quality: locally, conditions have gotten much better, but we still have to be wary of the air we share with regions. other.
Recent air quality trends
Indeed, North Carolina air quality continues to improve, and we can gauge that change using ozone design value. Design value is a statistic that describes the air quality status of a given location relative to the level of the National Ambient Air Quality Standards (NAAQS), set by the EPA. Design ozone values are calculated using a three-year average of the fourth highest average daily ozone concentration over 8 hours measured at an air quality monitor.
A number of factors – including (but not limited to) better fuel efficiency for cars, better industrial controls and tighter environmental regulations – have led to emissions levels precursors required for lower ozone formation.
As ozone levels drop, the number of days above the threshold is also reduced. At the turn of the millennium, we averaged 100 or more Code Orange days per year, with about a third of those days reaching Code Red, or Unhealthylevels.
Starting around 2012, overshoot days became rarer, with an average of only a handful of Code Orange days per year and only one Code Red day since 2013. You can learn more about the values. North Carolina’s ozone design and even how they compare to other states, by exploring Ozone design value prediction tool.
Our growing ozone climate
Together with the reduction of precursor pollutants such as nitrogen oxides (NOx) and volatile organic compounds (VOCs) that lead to ozone formation, the meteorological patterns typically associated with our peak ozone concentrations have also changed since a decade ago.
Historically, those high ozone days were easy to spot. Whenever an area of high pressure (at the surface and overhead) forms over the eastern United States during the summer months, parts of the state are likely to experience increased daily ozone concentrations.
The exact location and strength of the high pressure are not all that matters; As long as the sky is sunny and the wind is light, ozone levels can increase significantly due to much higher daily NOx and VOC emissions from pollution sources that were less controlled (at the time) such as power plants and automobiles.
Along with the decline in ozone precursor emissions – especially NOx – in recent years we have observed that a different atmospheric pattern is currently responsible for many of our highest ozone days in North Carolina.
Called the “Omega block,” the pattern is aptly named for its configuration: an area of high pressure surrounded by low pressure on both sides, much like the Greek letter omega .
The Omega blocks are famous for having prolonged warm and dry weather due to subducting air combined with high pressure. In addition, air masses below the high pressure are often trapped due to the inherent inward rotational circulation pattern.
This can lead to air mass stagnation and increased pollution, not only below the high pressure area, but also downwind of the area between the high and low pressure systems in the south. east, where pollution can sometimes propagate southward.
The pattern change observed during high ozone days in North Carolina in recent years could be a direct result of our air quality improvement. Due to the reduction in precursor emissions, it now takes a longer time for the air mass to stagnate before enough precursors can accumulate to produce high concentrations of ozone.
New era of NC . air quality information sharing
As part of an ongoing partnership between the State Climate Office and the NC DAQ, we are excited to announce the launch of our latest collaborative resource: Air quality portal. It will be the new hub for accessing NC DAQ’s daily air quality forecasts and discussions, along with a collection of tools, research, and educational information about the past, present, and future. future of the air we breathe.
It is our hope that this one-stop division will serve both the professional and public air quality communities. From sharing what’s outdoors today to showing local changes in air quality over the past decade, the Air Quality Portal has the answers.
Several tools are available – including Person reporting ambient information and we have been recently refurbished Wind Rose Tool – already available in the Air Quality Portal. It will even have a blog of its own, written by NC DAQ forecasters, with detailed information on air quality during this ozone season and beyond.
Although the frequency of high ozone days has decreased significantly over the past decade, in times when the air is still not satisfactory, we can turn to our abundance in terms of air quality and importance. weather monitoring, along with the knowledge we’ve gained in recent years, to provide more accurate, accurate, and informative forecasts for North Carolina.
