Measuring Submicron-Size Fractionated Particulate Matter on Aluminum Impactor Disks

Abstract

ABSTRACT. Submicron-sized airborne particulate matter (PM) is not collected well on regular quartz or glass fiber filter papers. We used a micro-orifice uniform deposit impactor (MOUDI) to fractionate PM into 6 size fractions and deposit it on specially designed high-purity thin aluminum disks. The MOUDI separated PM into fractions 56-100, 100-180, 180-320, 320-560, 560-1000, and 1000-1800 nm. Since the MOUDI has a low flow rate (30 L/min), it takes several days to collect sufficient carbon on 47-mm foil disks. The small carbon mass (20-200 g C) and large aluminum substrate (~25 mg Al) present several challenges to production of graphite targets for accelerator mass spectrometry (AMS) analysis. The Al foil consumes large amounts of oxygen as it is heated and tends to melt into quartz combustion tubes, causing gas leaks. We describe sample processing techniques to reliably produce graphitic targets for 14 C AMS analysis of PM deposited on Al impact foils.

Anomalous elevated radiocarbon measurements of PM2.5

“…Biomass burning from wild fires, residential wood burning and campfires, secondary organic aerosols (SOA) from vegetation, and food cooking produce high levels of PM with carbon that generally reside in the atmosphere for 3-7 days. Significant biogenic carbon has been reported in PM retained on a 2.5 lm filter (PM 2.5 ) and on smaller particles [1][2][3][4][5][6][7][8][9][10][11]. The high biogenic carbon content of PM in these studies was generally attributed to SOA whether they were collected at remote, rural or metropolitan sites.…”

“…Two component end member models are often used for source apportionment studies of particulate matter (PM) to estimate the contributions of major carbon sources [1][2][3][4][5][6][7][8][9][10][11]. Carbon-14 ( 14 C) can be used to distinguish between fossil carbon free of 14 C and biogenic carbon possessing a contemporary 14 C/C ratio.…”

“…The high biogenic carbon content of PM in these studies was generally attributed to SOA whether they were collected at remote, rural or metropolitan sites. Increased PM due to seasonal residential wood burning was the focus of two studies [3,8]. Bench and Herckes [1] applied source apportionment to the impact of haze in Yosemite National Park in California, USA.…”