Atmospheric organic aerosols have complex effects on global climate and human health. Acidity of atmospheric organic aerosol is a critical factor that can affect the amount of secondary organic aerosol formation, as many of the key multiphase chemical reactions are pH-dependent. However, scientific understanding is limited by the lack of accurate methods to directly measure submicron atmospheric organic aerosol acidity.  Specifically, there are no direct methods available to determine submicron atmospheric organic aerosol acidity using single particle methods and most methods rely on inferences or idealized modelling. Thus, a method is needed that can directly measure acidity for submicron atmospheric organic particles.<br/>This study developed a novel pH measurement using polymer degradation to determine the pH of individual submicron particles. The acidic aerosol particles with known pH were deposited on the polymer, and the polymer film was incubated with acidic particles impacted upon them for up to 15 days in a humidity chamber. Acidic particles were rinsed and the degraded polymer film caused by acidic particles was characterized using atomic force spectroscopy coupled with infrared spectroscopy (AFM-IR) and Raman micro-spectroscopy. Based on the relationship between pH and polymer degradation thickness, a pH measurement standard was determined and used to measure the acidity of laboratory generated secondary organic aerosol. It was found that decreasing acidity of aerosol increases polymer film degradation. The results from this study provide a new method to directly determine individual atmospheric organic aerosol acidity and improve current understanding of atmospheric organic aerosols.

Atmospheric organic aerosol acidity sensing via polymer degradation

2019 Fall National Meeting

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