S. G. Howell

A Field Intercomparison of Three Cascade Impactors

ABSTRACT Cascade impactors separate aerosol particles inertially and collect them for later analysis. While laboratory calibrations typically indicate performance close to design specifications, during field operation impactors are subject to a number of sampling artifacts, including particle bounce, inlet and internal losses, and particle size changes as pressure drops within the impactor. To test the vulnerability of some commonly used impactors to these problems under Held conditions, we participated in a shipboard intercomparison off the coast of Washington state between a micro-orifice uniform deposit impactor (MOUDI), a Berner low-pressure impactor, and a Sierra high-volume slotted impactor. Since there were some inconsistencies in the results, a second intercomparison was performed at Bellows Beach, Hawaii, between two MOUDIs and the Berner impactor. Impactor samples were analyzed for soluble inorganic ions including Na+, K+, Cl−, and NO− 3, primarily from large (>1 μm) sea salt particles and NH+ 4...

Variability of sulfate aerosol concentrations at Mauna Loa observatory, Hawaii

Daily total particulate matter observations of sulfate, sodium, and methanesulfonate were collected at Mauna Loa Observatory (19.54°N, 155.57°W, 3397m ASL) during 1995-2008. Observations were restricted to nighttime, downslope conditions and were thus representative of free tropospheric air masses. In this paper we focus analyses on 2008, when active volcanoes in Hawaii, Alaska, Indonesia, and elsewhere may have perturbed the northern hemisphere sulfur budget. The 2008 seasonal cycle of aerosol species was broadly consistent with the 1995-2008 mean, although the springtime peaks of anthropogenically-derived sulfate were larger than typical. Trajectories originated from East Asia less frequently and from North America more frequently in spring 2008 than in the long term data record, possibly linked to the strong La Nina conditions that year.