As we approach Canada Day (July 1) and Independence Day in the U.S. (July 4), our thoughts turn to the pyrotechnics that are a typical part of the celebrations. For a chemical engineer, pyrotechnics are a fascinating topic because they rely on rapid combustion reactions and the presence of various elements that give rise to the different colours. However, my research interests are in air quality and I’m at the Air & Waste Management Association conference in Chicago, so I’m going to review the air quality impact instead.
All combustion reactions can potentially generate “fine particulate”, which in the technical literature is usually referred to as “PM2.5” (particulate matter less than 2.5 µm in size). In recent years, PM2.5 has been of increasing regulatory interest and concern because of strong links to cardiac and respiratory disease. There have been other health impacts such as cancer and diabetes associated with PM2.5 exposure too. Some jurisdictions do not yet have PM2.5 regulations, but the World Health Organization (WHO) has recommended an upper limit of 25 µg/m3 (on a 24 hour average basis) in their air quality guidelines from 2005.
So what happens when fireworks explode in the air? We might expect that the rapid, explosive combustion will generate some PM2.5 (as well as larger particulate matter), but the only way to know for sure is to make some measurements. That’s what some research groups have done, and using Google Scholar I found a few research papers detailing their results. Following is a quick summary of key findings.
In 1999, Perry (J. Air & Waste Manage. Assoc., 49: 146-155) used a PM2.5 monitoring network in Washington state around July 4, and found that 18.5 µg/m3 of PM2.5 could be attributed to pyrotechnics (over and above the normal background 24 hour PM2.5). The elements K and S were major contributors (from black powder combustion), but other notable elements were Sr, V, Ti, Ba, Pb, Mg and Al (which are commonly used to generate the various colours). So by themselves, the fireworks didn’t exceed PM2.5 guidelines, but they could if the background level was more than 7 µg/m3. (If you live in Ontario and want to know what the PM2.5 concentration is in your location, here’s a website: http://www.airqualityontario.com/history/summary.php)
More recently, in 2010 Joly et al. (Atmos. Environ. 44: 4325-4329) reported on measurements taken at the 2007 Montréal International Fireworks Competition. In this case, more samples were taken at ground level and within the predicted plume of smoke using personal samplers, so it perhaps better represents the exposure of people attending the event or living downwind. In these findings, levels of PM2.5 were sustained above 1,000 µg/m3 during the display (about 45 minutes) and hit peaks of 10,000 µg/m3 for very short time periods. After the fireworks display ended, the PM2.5 quickly dropped back to background levels of 10 to 40 µg/m3. They also measured elevated concentrations of some elements such as K, Al, Ti and Mg.
So, what does this mean? The exposures during fireworks are potentially quite high but fairly brief, so on a 24 hour average basis it might be OK. On the other hand, there is not much known about the health effects of acute (brief) exposures to very high PM2.5 levels, or the elements that were identified in the particulate. Possibly the best advice is to try to stay up wind of fireworks displays, or avoid them altogether if you have pre-existing cardiopulmonary conditions or concerns (including asthma).