Long-range transport potential and atmospheric persistence of cyclic volatile methylsiloxanes based on global measurements. (August 2019)

• Record Type: Journal Article
• Authors: Xu, Shihe; Warner, Nicholas; Bohlin-Nizzetto, Pernilla; Durham, Jeremy; McNett, Debra
• Is Part Of: Chemosphere. Volume 228(2019)
• Page Start: 460
• Page End: 468
• Publication Date: 2019-08
• Subjects: D4 -- D5 -- D6 -- Spatial concentration gradients -- Air monitoring data -- Atmospheric persistence -- Long-range transport; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2019.04.130
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: This study investigates persistence (P) and long-range transport potential (LRTP) of cyclic volatile methylsiloxanes (cVMS) based on the field measurements in the Northern Hemisphere. The field data consisted of published outdoor air concentrations of octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6) at urban, suburban, rural and remote locations excluding the point sources. Three major trends were observed. First, D4 and D6 concentrations were correlated with measured concentrations for D5 at the same times and locations in the majority of the datasets, reflecting the common sources and similar removal mechanism(s) for these compounds. Second, as the sampling sites changed from the source to remote locations along a south-to-north transect, average cVMS concentrations in air decreased in an exponential manner. The empirical characteristic travel distances (eCTD) extracted from these spatial patterns were smaller than model estimated values and differed in order among individual compounds (D4 ∼ D5 < D6). Finally, D5/D6 concentration ratios were also found to decrease exponentially along the same spatial gradient, contrary to model predictions of an increase based on current knowledge of mechanisms controlling atmospheric cVMS degradation. These findings suggest that there may be additional removal process(es) for airborne cVMS, currently not accounted for, that requires further elucidation. Highlights: Good interspecies correlations found between measured airborne cVMS concentrations. Airborne cVMS concentrations and D5/D6 concentration ratios decrease in south-to-north spatial pattern. Analysis of spatial patterns suggests possible additional degradation mechanism(s) for cVMS in the atmosphere.