Aerosol particles have been linked to both human health concerns and global warming. Particles 2.5µm in diameter or less are most dangerous to human health. In this study we sampled particles with diameters between 0.10 and 2.5µm in Northfield, MN, a rural farming town 45 miles south of Minneapolis/St. Paul. The chemical composition of the aerosol particles was measured using an Aerosol Time-of-Flight Mass Spectrometer (ATOFMS), which provides us direct information about particle mixing state. Particles are grouped into classes based on their chemical composition, using K-means clustering. Particle classes can be used to identify the particle source. This allows us to monitor when, where, and how much particulate matter is generated by a specific source.<br/>The ATOFMS has a size-dependent particle detection efficiency, and because of matrix effects in the ionization process, individual peak areas do not directly represent the concentration of species in the particles analyzed. Healy, et al., (Atmos. Chem. Phys., 2013, 13, 9479.) have recently developed a method to calibrate these parameters based on measurements with co-located size and composition measurements. Here, we explore the possibility of accomplishing this without the co-located instruments. In order to scale the number of particles detected by the ATOFMS to the total number of particles in the air, number concentrations sorted by size were measured using a Scanning Mobility Particle Sizer (SMPS, 0.010 – 0.600 µm) and Aerodynamic Particle Sizer (APS, 0.500 – 20.00 µm) in parallel with the ATOFMS. Detection efficiency curves were created by dividing the merged SMPS-APS number concentrations by ATOFMS particle counts. We have investigated the dependence of the ATOFMS detection efficiency on time of day or day of week. These curves are then used to convert ATOFMS particle counts into total number concentrations when the SMPS-APS was not running. From this, we calculated total number concentrations of particles sorted by size, chemical composition, and time. In order to compare our results to standards and regulations, we convert number concentration into mass concentration by assuming that all particles are spherical with a uniform density. This provides mass concentrations of particles sorted by time, size and class/source. Obtaining estimates of individual chemical species in the particles will be explored.

Quantitative analysis of single-particle mass spectra acquired in Northfield, MN

249th National Meeting (2015)

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