8 research outputs found
Wideband Characteristic Basis Functions in Radiation Problems
In this paper, the use of characteristic basis function (CBF) method, augmented by the application of asymptotic waveform evaluation (AWE) technique is analyzed in the context of the application to radiation problems. Both conventional and wideband CBFs are applied to the analysis of wire and planar antennas
Occurrence and Seasonality of Cyclic Volatile Methyl Siloxanes in Arctic Air
Cyclic volatile methyl siloxanes (cVMS) are present in technical applications and personal care products. They are predicted to undergo long-range atmospheric transport, but measurements of cVMS in remote areas remain scarce. An active air sampling method for decamethylcyclopentasiloxane (D5) was further evaluated to include hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), and dodecamethylcyclohexasiloxane (D6). Air samples were collected at the Zeppelin observatory in the remote Arctic (79° N, 12° E) with an average sampling time of 81 ± 23 h in late summer (August−October) and 25 ± 10 h in early winter (November−December) 2011. The average concentrations of D5 and D6 in late summer were 0.73 ± 0.31 and 0.23 ± 0.17 ng/m3, respectively, and 2.94 ± 0.46 and 0.45 ± 0.18 ng/m3 in early winter, respectively. Detection of D5 and D6 in the Arctic atmosphere confirms their long-range atmospheric transport. The D5 measurements agreed well with predictions from a Eulerian atmospheric chemistry−transport model, and seasonal variability was explained by the seasonality in the OH radical concentrations. These results extend our understanding of the atmospheric fate of D5 to high latitudes, but question the levels of D3 and D4 that have previously been measured at Zeppelin with passive air samplers.acceptedVersio
Occurrence and seasonality of cyclic volatile methyl siloxanes in Arctic air
Cyclic volatile methyl siloxanes (cVMS) are present in technical applications and personal care products. They are predicted to undergo long-range atmospheric transport, but measurements of cVMS in remote areas remain scarce. An active air sampling method for decamethylcyclopentasiloxane (D5) was further evaluated to include hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), and dodecamethylcyclohexasiloxane (D6). Air samples were collected at the Zeppelin observatory in the remote Arctic (79° N, 12° E) with an average sampling time of 81 ± 23 h in late summer (August−October) and 25 ± 10 h in early winter (November−December) 2011. The average concentrations of D5 and D6 in late summer were 0.73 ± 0.31 and 0.23 ± 0.17 ng/m3, respectively, and 2.94 ± 0.46 and 0.45 ± 0.18 ng/m3 in early winter, respectively. Detection of D5 and D6 in the Arctic atmosphere confirms their long-range atmospheric transport. The D5 measurements agreed well with predictions from a Eulerian atmospheric chemistry−transport model, and seasonal variability was explained by the seasonality in the OH radical concentrations. These results extend our understanding of the atmospheric fate of D5 to high latitudes, but question the levels of D3 and D4 that have previously been measured at Zeppelin with passive air samplers
Calibration and Application of a Passive Air Sampler (XAD-PAS) for Volatile Methyl Siloxanes
Because
the atmosphere is key to understanding the environmental
behavior of volatile methyl siloxanes (VMS), a variety of reliable
air sampling methods are needed. The purpose of this study was to
calibrate and evaluate an existing, polystyrene–divinylbenzene
copolymeric resin-based passive air sampler (XAD-PAS) for VMS. Sixteen
XAD-PAS were deployed for 7–98 days at a suburban site in Toronto,
Canada, while the VMS concentration in air was monitored by an active
sampling method. This calibration and a subsequent field test further
allowed for investigation of the temporal and spatial variability
of VMS in the region. Uptake in the XAD-PAS of octamethylcyclotetrasiloxane
(D4), decamethylcyclopentasiloxane (D5), and three linear VMS was
linear throughout the whole deployment period. Sampling rates were
between 0.4 and 0.5 m<sup>3</sup>/day. The XAD-PAS measured ∑VMS
concentrations ranged from nondetects in rural areas (<i>n</i> = 3), to 169 ± 49 ng/m<sup>3</sup> in the urban region (<i>n</i> = 21), to levels above 600 ng/m<sup>3</sup> at sewage
treatment plants (<i>n</i> = 2). Levels and composition
of VMS within the urban area were remarkably uniform in space. Levels,
but not composition, were highly variable in time and weakly correlated
with temperature, wind speed, and wind direction