Quantitative sampling using an Aerodyne aerosol mass spectrometer 2. Measurements of fine particulate chemical composition in two U.K. cities

Abstract

In part 1 of this series, techniques for generating quantitative information on fine airborne particulate‐size and chemically resolved mass concentration from an Aerodyne aerosol mass spectrometer were introduced. Presented here are the results generated using these techniques from sampling U.K. urban air with such an instrument in Edinburgh during October 2000 and in Manchester during July 2001 and January 2002. Data on the total mass concentrations and size‐resolved mass distributions of nitrate, sulfate, and organic compounds were obtained for all three campaigns and compared with data from other sources, including a micro‐orifice uniform deposit impactor, total particle numbers, CO and NOx concentrations, local wind speed and temperature, and back trajectory analysis. All three locations showed evidence for emissions from local transport, with a mass modal aerodynamic diameter of around 100–200nm. This mode was dominated by hydrocarbons showing little evidence of oxidization. The three sites also exhibited a larger mode consisting of inorganic chemicals and oxidized organics, which appeared to be governed by sources external to the cities and showed evidence of internal mixing. The mass modal aerodynamic diameter varied between approximately 200–500 nm during the winter and 500–800 nm during the summer. The summer also showed an increased mass loading without an increase in total particle number. Evidence of material building up and ageing in the atmospheric surface layer during periods of low wind speeds was also observed.

Characterization of urban and rural organic particulate in the Lower Fraser Valley using two Aerodyne Aerosol Mass Spectrometers

“…This mode was principally composed of organic material with very small concentrations of inorganic species. This finding is consistent with previous observations made at other urban sites in the UK and the US Allan et al, 2003b;Drewnick et al, 2004b). The small organic mode appears to be characteristic of urban sites and fresh emissions.…”

“…The major source of these trace gases in urban environments is from motor vehicle exhaust (GVRD, 2002), and the strong correlation suggests that combustion-related emissions (with traffic likely representing a large fraction) are the main source of the small organic mode at Slocan Park urban site. This is consistent with many other studies including our previous urban measurements in two major UK cities (Allan et al, 2003b) Experiments performed in our laboratories have shown that mass spectra obtained using the AMS compare well to the NIST standard library of mass spectra for a range of chemical compounds with the exception of di-and poly carboxylic acids and humiclike substances, where m/z 44 (CO 2 + ) was found to be much more pronounced in the AMS spectra. The enhanced m/z 44 signal was coupled with a very strong peak at m/z 18 indicative of H 2 O + , implying thermal breakdown of the carboxylic acid group on the vaporizer.…”

“…Since the accumulation mode aerosol at Slocan contained a significant amount of ammonium sulphate mass and the sampling relative humidity was consistently low, a CE sulphate =50% is used. This work and previous studies (Allan et al, 2003b) provide indirect evidence that the organic and inorganic components in the accumulation mode are internally mixed based on the similar temporal variability and shape of their modes. It is therefore reasonable to assume a CE of 50% for accumulation mode nitrate and organics.…”

“…10 classify organic particulate measured at urban locations in Manchester, UK (Allan et al, 2003b) (Panel A), Slocan Park, Canada (Panel B) and at a rural location in Langley, Canada (Panels C and D) as a function of the CO and O 3 concentrations observed at these locations during the same measurement periods. Each panel (A-D) shows two organic mass size distributions averaged over conditionally selected periods.…”

“…In the MS mode the averaged chemical composition of the non-refractory aerosol components is determined by scanning the full mass spectrum (1-300 m/z units) with the quadrupole mass spectrometer identification and quantitative calibrations of chemical species are presented in Jimenez et al (2003a). A method for calculating a total organic mass size distribution from a combination of the pre-selected ToF mass fragments and the ensemble MS was described in a previous publication (Allan et al, 2003b).…”