Biogenic Emissions and Nocturnal Ozone Depletion Events at the Amphitrite Point Observatory on Vancouver Island

Routine monitoring stations on the west coast of North America serve to monitor baseline levels of criteria pollutants such as ozone (O3) arriving from the Pacific Ocean. In Canada, the Amphitrite Point Observatory (APO) on Vancouver Island has been added to this network to provide regional baseline measurements. In 2014, McKendry, I. G., Christensen, E., Schiller, C., Vingarzan, R., Macdonald, A. M., & Li, Y. (2014) reported frequent nocturnal O3 depletion events (ODEs) at APO that generally correlated with alongshore winds, elevated concentrations of carbon dioxide (CO2), and stable boundary layer conditions but the cause (causes) for this remains (remain) unclear. This manuscript presents results from the Ozone-depleting Reactions in a Coastal Atmosphere (ORCA) campaign, which took place in July 2015 to further investigate ODEs at APO. In addition to the long-term measurements at the site (e.g., CO2 and O3 mixing ratios), abundances of biogenic volatile organic compounds (BVOC) and aerosol size distributions were quantified. On the majority of measurement nights, ODEs were observed and characterized by a simultaneous increase in CO2 and BVOC abundances, in particular of limonene, a terpene 2.5 times more reactive with respect to oxidation by O3 than other monoterpenes. Back trajectory calculations showed that ODEs occurred mainly in air masses originating from the west-northwest where the air would have travelled parallel to the coastline and above kelp forests. Head-space analyses of seaweed samples showed that bull kelp is a source of gas-phase limonene, consistent with its high relative abundance in air masses from the west-northwest sector. However, the enhanced terpene and CO2 content showed that the air likely also came in contact with terrestrial vegetation via mesoscale transport phenomena (such as slope flows and land–sea breeze circulations) that were generally poorly captured by the back trajectories. The absence of aerosol growth during ODEs indicates that dry deposition is likely the primary O3 loss mechanism.

Keywords

marine boundary layer, ozone depletion, coastal zone, monoterpene emissions, kelp, limonene

Citation

Tokarek, T. W., Brownsey, D. K., Jordan, N., Garner, N. M., Ye, C. Z., Assad, F. V., Peace, A., Schiller, C. L., Mason, R. H., Vingarzan, R., & Osthoff, H. D. (2017). Biogenic emissions and nocturnal ozone depletion events at the Amphitrite Point Observatory on Vancouver Island. Atmosphere-Ocean, 55(2), 121-132. http://dx.doi.org/10.1080/07055900.2017.1306687

URI

http://hdl.handle.net/1880/113538

Collections

Science Research & Publications

Full item page