The air we breathe

Ben Kennedy, SPARK Writer | With every breath we take, we can inhale droplets of liquid, dust and even microscopic fungi. These solid and liquid particles, known as aerosols, modify our atmosphere through chemical reactions and are responsible for the destruction of ozone, as well as being important seeds for cloud formation. Chemistry professor Parisa Ariya's research suggests that living aerosols may affect many other types of aerosols, and that despite their relatively low abundance, these airborne critters may be critical to the balance of our climate.

Chemistry professor Parisa Ariya
Claudio Calligaris

All aerosols related to biological activity are called bioaerosols. Our current models of global climate do not account for bioaerosols because it was assumed that few organisms survive for long floating around in our atmosphere, due to extreme temperature variation and lack of food. Despite this, microbiologists have seen over the past few decades that many organisms can survive for long periods in our atmosphere.

As an atmospheric chemist, Ariya gained international recognition studying halogens and mercury aerosols in the Arctic. Her current study of bioaerosols is a new direction for her research. Ariya openly admitted that "Initially, I had no clue about microbiology, and learned about it while collaborating with microbiologists." Now she also works with physicists and atmospheric scientists, and runs three state-of-the-art labs where chemical reactions involving aerosols are analyzed.

Ariya's new direction evolved from a timely "goof" by one of her postdoctoral fellows. An experiment had been set up to investigate reactions between ozone and an organic solution. The researcher accidentally left a valve open on the reaction chamber and over the weekend a biological sludge formed on the windows of the chamber. Ariya explained that the micro-organisms contained in the laboratory air gained access to the experiment and grew by eating the organic solution. Those micro-organisms drastically changed the experimental results, producing a variety of new bioaerosols and completely depleting the organic solution. This sparked the idea that bioaersosols, airborne micro- organisms and their by-products may have a critical impact on our atmosphere. Until recently, researchers in the field of atmospheric chemistry had presumed that the effects of the bioaerosols were insignificant compared to the non-biological reactions that constantly occur in our atmosphere.

The initial results are encouraging: Ariya has measured rates of bioaerosol-driven chemical reactions and has shown that they can be faster than non-biological reactions, although these rates vary according to the species of micro-organisms and conditions, such as temperature and humidity, in the reaction chamber. She has also shown that bioaerosols can cause chemical changes in surrounding aerosols just by touching them. This significantly increases their impact, because it means that even dead micro-organisms can affect the chemistry of the atmosphere.

Ariya has satellite images that show large clouds of aerosols travelling across the globe. People in Montreal may remember ash from forest fires in Northern Quebec blowing over the city, but dust from as far away as the Sahara can also reach Montreal. In all likelihood, bioaerosols are within the aerosol clouds that circulate in our atmosphere.

The complex nature of bioaerosols means that their precise global importance is still unknown. Besides incorporating bioaerosol reactions into global chemical and climate models, Ariya also wants to determine whether bioaerosols play significant roles in the chemistry of snow. Fresh snow landing on your tongue may seem less refreshing if Ariya shows that it is full of bugs.

McGill's SPARK program (Students Promoting Awareness of Research Knowledge) is funded by NSERC and run by the Faculty of Education, VP Research Office and the University Relations Office. See www.spark.mcgill.ca for more information and articles.