Professor Murray V. Johnston

Analytical Chemistry

Current Research

On-line analysis of airborne particles by aerosol mass spectrometry is an important tool for environmental and atmospheric chemistry. Airborne particles, whether of anthropogenic or natural origin, can strongly influence human health and global climate. Aerosol mass spectrometers have made it possible to study the chemical composition of particles in the atmosphere as a function of rapid changes in meteorology and to draw detailed associations between wind direction and particles that are emitted from specific sources. Laboratory experiments of gas-particle kinetics provide a fundamental chemical basis for understanding how particles nucleate, grow and transform in air. An important emerging area of aerosol mass spectrometry is the study of fate and transport of engineered nanoparticles in the environment.

The Johnston group has developed a variety of aerosol mass spectrometers for use in laboratory and field measurements. A real-time single particle mass spectrometer (RSMS) provides size resolved single particle analysis above 50 nm in diameter. A nanoaerosol mass spectrometer (NAMS) provides single particle analysis in the 7 nm to 30 nm size range. A photoionization aerosol mass spectrometer (PIAMS) provides near real-time analysis of organic components in airborne particles using vacuum ultraviolet radiation for soft ionization. Particles can also be collected and analyzed with conventional mass spectrometers in the departmental mass spectrometry facility, including a 7 Tesla Fourier transform mass spectrometer and a quadrupole – time of flight mass spectrometer. A variety of equipment is available to generate test and calibration aerosols, to study aerosol reactions and to independently measure particle size distributions and gas phase reactant concentrations.

Johnston’s group has performed field measurements of ambient particulate matter around the world. They also make use of trailers at air monitoring sites in the State of Delaware at Wilmington and Lewes for ambient measurements in urban and coastal environments. Additional information on current laboratory and field projects can be found at the group web site.

Nano Aerosol Mass Spectrometer

Representative Publications

K. Adou and M. V. Johnston “Flow Interface for Charge Reduced Electrospray of Nanoparticle Solutions,” Analytical Chemistry, (2009) 81, 10186-10192.
B. R. Bzdek, D. P. Ridge and M. V. Johnston “Amine exchange into ammonium bisulfate and ammonium nitrate nuclei,” Atmospheric Chemistry and Physics, (2010) 10, 3495-3503.
B. R. Bzdek and M. V. Johnston “New Particle Formation and Growth in the Troposphere,” Analytical Chemistry, (2010) 82, 7871-7878.
C. A. Zordan, M. R. Pennington and M. V. Johnston “Elemental Composition of Nanoparticles with the Nano Aerosol Mass Spectrometer,” Analytical Chemistry, (2010) 82, 8034-8038.
Y. Q. Gao, W. A. Hall IV and M. V. Johnston “Molecular Composition of Monoterpene Secondary Organic Aerosol at Low Mass Loading,” Environmental Science and Technology, (2010) 44, 7897-7902.
J. P. Klems, M. R. Pennington, C. A. Zordan and M. V. Johnston “Ultrafine Particles near a Roadway Intersection: Origin and Apportionment of Fast Changes in Concentration,” Environmental Science and Technology, (2010)
44, 7903-7907.
B. R. Bzdek, D. P. Ridge and M. V. Johnston “Size- Dependent Reactions of Ammonium Bisulfate Clusters with Dimethylamine,” Journal of Physical Chemistry A, (2010) 114, 11638-11644.