Laboratory mass spectrometry of intact atmospherically-relevant particles

The physical and chemical properties of atmospheric aerosols profoundly impact the climate and human health. With diameters from sub-nanometer to tens of microns, a multitude of different experimental techniques suited to specific size ranges must be employed to characterize them. While mass spectrometry can be performed on particles of any size by destroying them and characterizing their molecular and atomic compositions, the masses of atmospheric nanoparticles with sizes below 10 nm can be measured with enough precision to observe discrete changes of their chemical composition while they remain intact. This enables direct study of their structure and reactivity in well-controlled laboratory experiments, complementing ambient field measurements. Here, we review the application of mass spectrometry and unique experiments based on mass spectrometers to measure the composition, stability, structure, and formation mechanisms of aerosol particles. We discuss the instrumentation employed in these experiments, including ion mobility separation, ion trap reactivity, and laser spectroscopy, that are often combined with mass spectrometry, and highlight illustrative examples of these techniques to prototypical atmospheric nanoparticles. We also highlight emerging mass spectrometry techniques that could extend these studies to larger nanoparticles and enable new insights into current unsolved problems involving atmospheric nanoparticles.