Quantification of aerosol chemical composition using continuous single particle measurements
Mass concentrations of sulphate, nitrate, ammo- nium, organic carbon (OC), elemental carbon (EC) were de- termined from real time single particle data in the size range 0.13.0µm measured by an Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) at urban and rural sites in Canada. To quantify chemical species within individual particles mea- sured by an ATOFMS, ion peak intensity of m/z 97 for sul- phate, 62 for nitrate, +18 for ammonium, +43 for OC, and +36 for EC were scaled using the number and size distribu- tion data by an Aerodynamic Particle Sizer (APS) and a Fast Mobility Particle Sizer (FMPS). Hourly quantified chemical species from ATOFMS single-particle analysis were com- pared with collocated fine particulate matter (aerodynamic diameter<2.5 µm, PM2.5) chemical composition measure- ments by an Aerosol Mass Spectrometer (AMS) at a rural site, a Gas-Particle Ion Chromatograph (GPIC) at an urban site, and a Sunset Lab field OCEC analyzer at both sites. The highest correlation was found for nitrate, with correla- tion coefficients (Pearson r) of 0.89 (ATOFMS vs. GPIC) and 0.85 (ATOFMS vs. AMS). ATOFMS mass calibration factors, determined for the urban site, were used to calcu- late mass concentrations of the major PM2.5 chemical com- ponents at the rural site near the US border in southern On- tario. Mass reconstruction using the ATOFMS mass calibra- tion factors agreed very well with the PM2.5 mass concentra- tions measured by a Tapered Element Oscillating Microbal- ance (TEOM, r =0.86) at the urban site and a light scattering monitor (DustTrak, r =0.87) at the rural site. In the urban area nitrate was the largest contributor to PM2.5 mass in the winter, while organics and sulphate contributed64%of the summerPM2.5 in the rural area, suggesting a strong influence of regional/trans-boundary pollution. The mass concentra- tions of five major species in ten size-resolved particle-types and aerosol acidity of each particle-type were determined for the rural site. On a mass basis sulphate and OC rich particle- types (OC-S and OC-S-N) accounted for up to 59% of the particles characterized and aerosols were weakly acidic in the rural area. This is the first study to estimate hourly quantita- tive data of sulphate, nitrate, ammonium, OC and EC in am- bient particles from scaled ATOFMS single particle analysis; these were closely comparable with collocated high time res- olution data of sulphate, nitrate and ammonium detected by AMS and GPIC.