Characterization, composition and source identification of Iraqi aerosols

Abstract

Soldiers that are deployed overseas are breathing ambient air containing concentrations of fine particulate matter known to cause adverse effects to human health. A study initiated in 2008 was designed to determine the concentrations and compositions of fine particulate matter in Baghdad, Iraq. This study used a Davis Rotating drum Unit for Monitoring (DRUM) aerosol impactor to continuously collect size (eight stages between 0.09 and 10 microns in aerodynamic diameter) and time (hour and a half resolution) resolved aerosol samples for mass concentration and elemental composition analyses. Results of this study show that fine particulate matter is associated with geogenic and anthropogenic source emissions. Trace metal concentrations combined with vanadium (V) can be correlated to industrial and urban source emissions, while lead (Pb) is associated with geogenic and anthropogenic sources. The mass loadings on the finest size fractions (0.09-0.26) of the DRUM aerosol impactor (0.09-0.34 microns) correlated with the mass loadings of coarse particles (2.5-10.0 microns) as both had similar elemental mass ratios, and thus were interpreted as having a common geogenic source. Brittle fragmentation theory was incorporated in this study to assist in explaining particle behavior and was effective at explaining particle breakdown in no wind/low wind situations. The aerosol particle samples collected during this study contained high total soil mass concentrations in all size stages. However, a peak in mass concentration was observed within the ultrafine (0.09-0.26 microns) stage that is not consistent with current hypotheses about the size distribution of mechanically produced soil particles through brittle fragmentation theory. The production of soil particles cannot fully be explained by brittle fragmentation theory during high wind scenarios. It is more likely that a combination of processes (brittle fragmentation, saltation, long-range transport, and midair collisions during high wind conditions) occur that result in excess mechanical grinding to produce ultrafine soil particles during high wind scenarios. A calibration study was conducted on the 8-stage DRUM aerosol impactor to ensure that the production of ultrafine particles was not a result of brittle minerals (calcium sulfate, sodium bicarbonate, and finely ground quartz) breaking down in the sampler. Mineral particles were not observed on the smallest size fractions under either 'wind' (4.1 m/s) or 'high wind' (8.3 m/s) conditions. This fact confirmed that the particles were not breaking down into smaller particles than observed in the initial size distribution characterized by an optical particle counter. These findings suggest that the increases in soil element concentrations on the DRUM stages seen in data sets from Iraq and White Sands, NM, are not a product of particle fragmentation during sampling. The production of these particles are important in that the fine particulate matter concentrations frequently exceed military exposure guidelines of 65 μg m⁻³ and individual constituents, such as lead, exceed U.S. national ambient air quality standards designed to protect human health.