Baseline characterisation of source contributions to daily-integrated PM2.5 observations at Cape Grim using Radon-222

Numerical analysis of two-filter method for continuous measurement of airborne Rn-222

The two-filter method enables the continuous measurement of airborne Rn-222 via simultaneously sampling and counting. However, the slow time response of the two-filter detector and the overlapping counting data derived from the intervallic data acquisition make the interpretation of measurement results complicated. A valid data analysis to exactly match the series of counting data with the corresponding radon concentrations is desired. In this work, the continuous sampling and counting processes of the two-filter method is depicted numerically and the calculation of radon concentration from the raw counting data is given with detailed formulas. The numerical model is used to quantitatively investigate the influences of several key factors, including the volume of the radon delay chamber (5-10 000 l), the flow rate of air sampling (2.5-1000 l min^-1) and the interval time of data acquisition (5-120 min), on the measurement sensitivity and accuracy, which provides an approach for the optimization of the design and measurement settings of a specific two-filter detector in relation to these aspects.

Composition of Clean Marine Air and Biogenic Influences on VOCs during the MUMBA Campaign

Volatile organic compounds (VOCs) are important precursors to the formation of ozone and fine particulate matter, the two pollutants of most concern in Sydney, Australia. Despite this importance, there are very few published measurements of ambient VOC concentrations in Australia. In this paper, we present mole fractions of several important VOCs measured during the campaign known as MUMBA (Measurements of Urban, Marine and Biogenic Air) in the Australian city of Wollongong (34°S). We particularly focus on measurements made during periods when clean marine air impacted the measurement site and on VOCs of biogenic origin. Typical unpolluted marine air mole fractions during austral summer 2012-2013 at latitude 34°S were established for CO2 (391.0 ± 0.6 ppm), CH4 (1760.1 ± 0.4 ppb), N2O (325.04 ± 0.08 ppb), CO (52.4 ± 1.7 ppb), O3 (20.5 ± 1.1 ppb), acetaldehyde (190 ± 40 ppt), acetone (260 ± 30 ppt), dimethyl sulphide (50 ± 10 ppt), benzene (20 ± 10 ppt), toluene (30 ± 20 ppt), C8H10 aromatics (23 ± 6 ppt) and C9H12 aromatics (36 ± 7 ppt). The MUMBA site was frequently influenced by VOCs of biogenic origin from a nearby strip of forested parkland to the east due to the dominant north-easterly afternoon sea breeze. VOCs from the more distant densely forested escarpment to the west also impacted the site, especially during two days of extreme heat and strong westerly winds. The relative amounts of different biogenic VOCs observed for these two biomes differed, with much larger increases of isoprene than of monoterpenes or methanol during the hot westerly winds from the escarpment than with cooler winds from the east. However, whether this was due to different vegetation types or was solely the result of the extreme temperatures is not entirely clear. We conclude that the clean marine air and biogenic signatures measured during the MUMBA campaign provide useful information about the typical abundance of several key VOCs and can be used to constrain chemical transport model simulations of the atmosphere in this poorly sampled region of the world.