Size-resolved,real-time measurement of water-insoluble aerosols in metropolitan Atlanta during the summer of 2004 |
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| Institution: | 1. Department of Pediatrics, Emory University School of Medicine, 2015 Uppergate Drive, Atlanta, GA 30322, USA;2. School of Civil and Environmental Engineering, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332, USA;3. School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332, USA;1. Laboratory for Atmospheric Research, Dept. of Civil & Environmental Engineering, Washington State University, Pullman, WA, USA;2. African Centre for Technology Studies, Nairobi, Kenya;3. Dept. of Civil & Environmental Engineering, Rice University, Houston, TX, USA;4. Houston Advanced Research Center, The Woodlands, TX, USA;1. Aerosol & Atmospheric Research Laboratory, Department of Physics, Sri Krishnadevaraya University, Anantapur 515 003, Andhra Pradesh, India;2. Space Physics Laboratory, Vikram Sarabhai Space Centre, Trivandrum 695 022, Kerala, India;1. Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA;2. National Park Service/CIRA, Colorado State University, Fort Collins, CO, USA |
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| Abstract: | During the month of August 2004, the size-resolved number concentration of water-insoluble aerosols (WIA) from 0.25 to 2.0 μm was measured in real-time in the urban center of Atlanta, GA. Simultaneous measurements were performed for the total aerosol size distribution from 0.1 to 2.0 μm, the elemental and organic carbon mass concentration, the aerosol absorption coefficient, and the aerosol scattering coefficient at a dry (RH=30%) humidity. The mean aerosol number concentration in the size range 0.1–2.0 μm was found to be 360±175 cm?3, but this quantity fluctuated significantly on time scales of less than one hour and ranged from 25 to 1400 cm?3 during the sample period. The mean WIA concentration (0.25–2.0 μm) was 13±7 cm?3 and ranged from 1 to 60 cm?3. The average insoluble fraction in the size range 0.25–2.0 μm was found to be 4±2.5% with a range of 0.3–38%. The WIA population was found to follow a consistent diurnal pattern throughout the month with concentration maxima concurring with peaks in vehicular traffic flow. WIA concentration also responded to changes in meteorological conditions such as boundary layer depth and precipitation events. The temporal variability of the absorption coefficient followed an identical pattern to that of WIA and ranged from below the detection limit to 55 Mm?1 with a mean of 8±6 Mm?1. The WIA concentration was highly correlated with both the absorption coefficient and the elemental carbon mass concentration, suggesting that WIA measurements are dominated by fresh emissions of elemental carbon. For both the total aerosol and the WIA size distributions, the maximum number concentration was observed at the smallest sizes; however the WIA size distribution also exhibited a peak at 0.45 μm which was not observed in the total population. Over 60% of the particles greater than 1.0 μm were observed to be insoluble in the water sampling stream used by this instrumentation. Due to the refractive properties of black carbon, it is highly unlikely that these particles could be composed of elemental carbon, suggesting a crustal source for super-micron WIA. |
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