Environmental & Climate Sciences Department Seminar

A Fast Integrated Mobility Spectrometer (FIMS) based on image processing was developed for rapid measurements of aerosol size distributions from 10 to 500 nm. The FIMS consists of a parallel plate classifier, a condenser, and a CCD detector array. Inside the classifier an electric field separates charged aerosols based on electrical mobilities. Upon exiting the classifier, the aerosols pass through a three-stage growth channel, where aerosols as small as 7 nm are enlarged to above 1 μm through water or heptanol condensation. Finally, the grown aerosols are illuminated by a laser sheet and imaged onto a CCD array. The images provide both aerosol concentration and position, which directly relate to the aerosol size distribution after data inversion, considering the FIMS transfer function, particle penetration efficiency, and multiple charging of aerosols. The parallel Comparisons between the FIMS and a scanning mobility particle sizer (SMPS) demonstrated excellent agreement when measuring aerosols with various size spectra, showing differences within 5% in average particle size and total number concentration. But by simultaneously measuring aerosols with different sizes, the FIMS provides aerosol size spectra nearly 100 times faster than the SMPS. Recent deployment onboard research aircraft demonstrated that the FIMS is capable of measuring aerosol size distributions in 1s, thereby offering a great advantage in applications requiring high time resolution. The deployment of the FIMS during the recent Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) campaign helped identify new particle formation in the decoupled layer of the marine boundary layer during cold air outbreak periods. The vertical profiles of the aerosol size distributions during these events further explained the fate and transport of the newly formed aerosols.