Abstract
Abstract. As one aspect of the NETwork on Climate and Aerosols: addressing key uncertainties in Remote Canadian Environments (NETCARE), measurements of the cloud condensation nucleation properties of 50 and 100 nm aerosol particles were conducted at Ucluelet on the west coast of Vancouver Island in August 2013. The overall hygroscopicity parameter of the aerosol (κambient) exhibited a wide variation, ranging from 0.14 ± 0.05 to 1.08 ± 0.40 (where the uncertainty represents the systematic error). The highest κ values arose when the organic-to-sulfate ratio of the aerosol was lowest and when winds arrived from the west after transport through the marine boundary layer. The average κambient during this time was 0.57 ± 0.16, where the uncertainty represents the standard deviation. At most other times, the air was predominantly influenced by both marine and continental emissions, which had lower average PM1 κambient values (max value, 0.41 ± 0.08). The two-day average aerosol ionic composition also showed variation, but was consistently acidic and dominated by ammonium (18–56% by mole) and sulfate (19–41% by mole), with only minor levels of sodium or chloride. Average κorg (hygroscopicity parameter for the aerosol's organic component) values were estimated using PM1 aerosol composition data and by assuming that the ratio of aerosol organic to sulfate mass is related directly to the composition of the size-selected particles.
Highlights
Atmospheric aerosol particles directly affect the Earth’s radiative budget by scattering and absorbing incoming solar radiation (Charlson et al, 1992)
During the entire campaign there were four types of air masses that arrived in Ucluelet: (a) air that was influenced by both marine and continental sources, (b) descending, non-boundary layer air from the west, (c) air predominantly from the west that was clearly from the marine boundary layer without continental influence, and (d) air that was within the marine boundary layer, originated from the west (i.e. Pacific Ocean), and spent time over Vancouver Island
An initial period where the trajectories were likely to be influenced by both marine and continental sources (i.e. air mass type (a), 7–12 August, representing trajectories that arrive from the north having travelled along the west coast of Vancouver Island and the BC mainland); second, an intermediate period of descending, nonboundary layer air from the west (i.e. air mass type (b), 14–16 and 23 August); third, a period of air that was clearly from the marine boundary layer to the west without continental influence (i.e. air mass type (c), 13 and 18–20 August); and a period of air that was within the marine boundary layer, originated from the west (i.e. Pacific Ocean), and spent time over Vancouver Island (i.e. air mass type (d), 21–22 August)
Summary
Atmospheric aerosol particles directly affect the Earth’s radiative budget by scattering and absorbing incoming solar radiation (Charlson et al, 1992). Yakobi-Hancock et al.: CCN activity of size-selected aerosol at a Pacific coastal location In both coastal and marine locations it is common for aerosol of anthropogenic and continental biogenic origin to be present, for instance, as a result of emissions by forests, populated areas, and shipping traffic. In this study we use the hygroscopicity parameter approach to report the CCN activity of 50 and 100 nm ambient aerosol particles that were present on the west coast of Vancouver Island (Ucluelet, British Columbia) in August 2013 These experiments were conducted as part of a campaign to examine cloud formation properties of marine aerosol, as one component of the NETCARE (the NETwork on Climate and Aerosols: addressing key uncertainties in Remote Canadian Environments) project (http://www.netcare-project.ca/). This information is used in conjunction with the ambient aerosol’s PM1 organic-to-sulfate ratio to provide one of the first estimates of the hygroscopicity parameter of organics contained within coastal ambient particles
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