Fireworks’ role in 4th of July, Diwali festival air quality

While many understand that wildfire smoke and visibly dark emissions from factories and vehicles contribute to poor air quality, it may be harder to grasp the role your local fireworks play since they are so short lived.

As Independence Day approaches each year, air quality forecasters look at the precipitation, cloud cover and wind forecast for any given area as per usual- then usually tack up the AQI by a couple more points.

Depending on if July 4 falls on a weekend day or not, this forecast becomes trickier as towns and individuals set off fireworks on days other than July 4th. Regardless, the cumulative amount of low-level smoke introduced to the atmosphere is not negligible when predicting air quality.

Understanding how the atmosphere evolves on any given day, particularly in the summertime, plays a significant role in how the smoke is dispersed:
- As the sun rises, sunshine heats the ground, which heats the air directly above the ground, which then rises and mixes with the cooler air above. As the day wears on, the mixing increases and infiltrates higher and higher into the atmosphere.
- Usually, this process helps to disperse early morning rush hour emissions. When the sun sets, the opposite occurs.
- When additional heating stops, the mixing process is stopped short, dooming everything in the lower atmosphere to stay there through the night. On the Fourth of July, this means that at sunset - right when the mixing stops - incredible amounts of firework smoke are suddenly trapped in the lowest level of the atmosphere.
- Therefore, overnight levels of particles and smoke in the air are significantly higher than they would be naturally, and are stuck that way until a sunny or breezy day mixes it away.

Forecasters must pay close attention to wind patterns, since smoke can be transported great distances overnight. For example, if there was a southwesterly breeze in the Northeast during the night of July 4th, very poor air quality would be in store for Connecticut and other places downwind of D.C., Baltimore, Philadelphia and New York City. (In fact, Connecticut experiences poor air quality due to emissions from these cities on a pretty regular basis. Future blog entry?)

If you’re interested in specific numbers, Dr. Marshall Shepherd wrote a timely piece on the topic this year, which you can find here.

For this article, he consulted satellite data that detects aerosols and particles in the atmosphere, and presented the data for the Atlanta area. His findings clearly show a big jump in particle pollution in the area in early July.

Since Independence Day fell on a Tuesday, many towns likely decided to set off fireworks the weekend before, therefore spreading the smokiness over the course of several days.

In State College, Pennsylvania, (where AccuWeather HQ is located), fireworks from Friday, June 30 through Tuesday, July 4 are likely the culprit for the early July jump in particle and aerosol measurements.
(If you would like to generate this graphic for your location, click here)

As dramatic as this increase may seem, the air quality in the U.S. doesn’t rise to especially dangerous levels often, even on the Fourth of July and New Years. On the Air Quality Index (AQI) scale of 0 to 500, it is rare for any location to exceed 150, even for one day.

In India, however - where air quality is already famously poor due to the climate and industrial economy - fireworks are also used by millions on religious holidays. On and following these holidays, the air quality index shoots off the charts - above an AQI of 500 - in many Indian cities for days at a time.

Diwali - the Hindu festival of lights - occurs every year in mid-October, and is celebrated by millions with feasting, praying and setting off copious amounts of fireworks. Smoke inundates the cities following Diwali celebrations, often with no help from the dry, stagnant weather of the dry season.

Despite government claims that efforts will be made to mitigate the increasingly poor air quality during the holiday season, the AQI regularly rises to extreme levels in India’s cities for several days following Diwali.

Above, a screenshot of post-Diwali AQI values throughout the capital city of New Delhi sits above an AirNow.gov AQI forecast for Southern California for July 15th (below), where hundreds of thousands of acres of wildfires are currently burning and creating a deteriorating air quality scenario.

It is obvious that densely populated, industry heavy Indian cities reach incomparably poor air quality levels following fireworks celebrations. Where residents of these cities anticipate days of Hazardous AQI, it is rare for any U.S. city to reach even very unhealthy levels at any time of year, even when surrounded by wildfires.

While fireworks are a fun and beautiful way to celebrate holidays of any kind, it is also important to keep in mind the lasting impact they can have on local air quality. Particle pollution tends to be more extreme in the wintertime, when the atmosphere mixes less than in the summer - keep this post in mind when New Years fireworks make city streets and your neighborhood hazy on the morning of Jan. 1.

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