Measurement of Ambient Aerosol Composition During the PMTACS-NY 2001 Using an Aerosol Mass Spectrometer. Part II: Chemically Speciated Mass Distributions

Ambient particulate mass distributions (10 min averages) for nitrate, sulfate, ammonium, and organic particles were obtained during the deployment of the aerosol mass spectrometer (AMS) in the PM2.5 Technology Assessment and Characterization Study– New York (PMTACS–NY) in Queens, New York in summer 2001. Nitrate and sulfate particles were found to be internally mixed and mainly represented by ammonium nitrate and ammonium sulfate. Their average mass distributions are monomodal, with mode diameters of 440 nm and 450 nm and distribution widths around 600 nm. The maximum of the ammonium mass distribution was found at 400 nm and its width was about 550 nm. The average mass distribution of organic particles was bimodal with maxima at 80 nm and 360 nm and widths of 80 nm and 700 nm. While most of these distributions did not exhibit any significant diurnal patterns, the relative intensity of the small particle mode of the organic particles (Dp < 120 nm) was found to be most intense during rush-hour times, indicating that the small organic particle fraction is mostly traffic related. Short-time averages of the size distributions, measured for different species independently, showed the ability of the AMS to track the growth and evolution of chemically distinct particles.