Identifying tropospheric baseline air masses at mauna loa observatory between 2004 and 2010 using radon-222 and back trajectories

dc.contributor.authorChambers, SDen_AU
dc.contributor.authorZahorowski, Wen_AU
dc.contributor.authorWilliams, AGen_AU
dc.contributor.authorCrawford, Jen_AU
dc.contributor.authorGriffiths, ADen_AU
dc.date.accessioned2015-09-28T06:17:56Zen_AU
dc.date.available2015-09-28T06:17:56Zen_AU
dc.date.issued2013-01-16en_AU
dc.date.statistics2015-09-26en_AU
dc.description.abstractWe use 7 years of hourly radon observations at Mauna Loa Observatory (MLO), together with 10-day back trajectories, to identify baseline air masses at the station. The amplitude of the annual MLO radon cycle, based on monthly means, was 98 mBq m–3 (39 –137 mBq m–3), with maximum values in February (90th percentile 330 mBq m–3) and minimum values in August (10th percentile 8.1 mBq m–3). The composite diurnal radon cycle (amplitude 49 mBq m–3) is discussed with reference to the influences of local flow features affecting the site, and a 3-hour diurnal sampling window (0730–1030 HST) is proposed for observing the least terrestrially influenced tropospheric air masses. A set of 763 baseline events is selected, using the proposed sampling window together with trajectory information, and presented along with measured radon concentrations as a supplement. This data set represents a resource for the selection of baseline events at MLO for use with a range of trace species. A reduced set of 196 “deep baseline” events occurring in the July–September window is also presented and discussed. The distribution (10th/50th/90th percentile) of radon in deep-baseline events (8.7/29.2/66.1 mBq m–3) was considerably lower than that for the overall set of 763 baseline events (12.3/40.8/104.1 mBq m–3). Results from a simple budget calculation, using sonde-derived mixing depths and literature-based estimates of oceanic radon flux and radon concentrations in the marine boundary layer, indicate that the main source of residual radon in the lower troposphere under baseline conditions at MLO is downward mixing from aged terrestrial air masses in the upper troposphere. © 2012, American Geophysical Union.en_AU
dc.identifier.citationChambers, S. D., Zahorowski, W., Williams, A. G., Crawford, J., & Griffiths, A. D. (2013). Identifying tropospheric baseline air masses at Mauna Loa Observatory between 2004 and 2010 using Radon-222 and back trajectories. Journal of Geophysical Research: Atmospheres, 118(2), 992-1004. doi:10.1029/2012jd018212en_AU
dc.identifier.govdoc6075en_AU
dc.identifier.issn2169-897Xen_AU
dc.identifier.issue2en_AU
dc.identifier.journaltitleJournal of Geophysical Research: Atmospheresen_AU
dc.identifier.pagination992-1004en_AU
dc.identifier.urihttp://dx.doi.org/10.1029/2012jd018212en_AU
dc.identifier.urihttp://apo.ansto.gov.au/dspace/handle/10238/6230en_AU
dc.identifier.volume118en_AU
dc.language.isoenen_AU
dc.publisherJohn Wiley and Sonsen_AU
dc.subjectRadonen_AU
dc.subjectTroposphereen_AU
dc.subjectPollutionen_AU
dc.subjectTerrestrial ecosystemsen_AU
dc.subjectRadioactive wastesen_AU
dc.subjectWinden_AU
dc.titleIdentifying tropospheric baseline air masses at mauna loa observatory between 2004 and 2010 using radon-222 and back trajectoriesen_AU
dc.typeJournal Articleen_AU
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