Let me introduce you to TORM, the total ozone reactivity monitor

An important part of my Academy Research Fellow project (2017-2022) funded by Academy of Finland was the development of an instrument to measure total ozone (O3) reactivity. The paper describing the method we use, based on an idea by Dr. Detlev Helmig, and developed together with his group, has just been published in Atmospheric Measurement Techniques.

At the time of my proposal submission in 2016, there had been only one publication on the topic of total O3 reactivity measurement by Prof. Jun Matsumoto (Waseda University, Tokyo, Japan). I was also aware of measurements that had been done by Dr. Helmig's group that had been presented at conferences. This is why I visited Prof. Matsumoto in Tokyo in December 2017 and then went to Boulder CO, U.S.A., with Anssi Liikanen, in January 2018. Anssi stayed almost two months to work in Dr. Helmig's laboratory, performing many tests on the total O3 reactivity monitor (TORM).

 

Figure 1. Left: TORM at the Toolik Field Station, Alaska, U.S.A. The wooden box contains the flasks forming the reactor and the rack underneath holds two ozone monitors. Right: Schematic of TORM as deployed at the University of Michigan Biological Station, taken from our published paper (Helmig et. al, 2022).

 

Compared to total hydroxyl radical (OH) reactivity measurements that we used earlier, total O3 reactivity measurements are more selective, as O3 reacts with fewer compounds than OH. O3 oxidize compounds that have a carbon-carbon double (C=C) bond in their chemical structures. Many emissions of natural origin into the atmosphere (biogenic emissions) include compounds such as terpenes, who do have at least one C=C bond. For this reason, we hoped to show with total O3 reactivity measurements that we are able to identify the chemical composition of these emissions in their totality. 

In 2020, Prof. William Bloss's group also published results of their total O3 reactivity measurements, but the main idea that makes TORM different from the other methods (Matsumoto, 2014; Sommariva et al., 2020), is that it uses a modified ozone monitor to measure directly the ozone loss in the instrument reactor, instead of relying on two different monitors to measure the same quantity. While the idea is very simple, it is not as straightforward as one might think in practice, which is why lots of testing was necessary to make the method reliable. All the details can be found in the published paper:

 

Helmig, D., Guenther, A., Hueber, J., Daly, R., Wang, W., Park, J.-H., Liikanen, A., and Praplan, A. P. (2022). Ozone reactivity measurement of biogenic volatile organic compound emissions. Atmos. Meas. Tech., 15, 5439–5454. doi:10.5194/amt-15-5439-2022.   

 

The original manuscript was submitted in October 2021. For a myriad of reasons, it took almost a year to address the reviewers comments, revise the manuscript, and correct the errors found during proofreading. Our efforts were important as this peer-reviewed and published paper describes TORM in detail. Two different versions of the instrument (the original one developed at the University of Colorado Boulder, and the other one built at the Finnish Meteorological institute) have been deployed in various location. Preliminary results seem to indicate that even from tree emissions, we cannot fully explain the measured total O3 reactivity with identified compounds. I will certainly report more about these results here, once published, so stay tuned!

References

• Matsumoto, J. (2014). Measuring Biogenic Volatile Organic Compounds (BVOCs) from Vegetation in Terms of Ozone Reactivity. Aerosol Air Qual. Res., 14, 197–206. doi:10.4209/aaqr.2012.10.0275.
• Sommariva, R., Kramer, L. J., Crilley, L. R., Alam, M. S., and Bloss, W. J. (2020). An instrument for in situ measurement of total ozone reactivity. Atmos. Meas. Tech., 13, 1655–1670. doi:10.5194/amt-13-1655-2020.