Semi-continuous measurement of chromophoric organic aerosols using the PILS-EEM-TOC system

Abstract

Atmospheric chromophoric organic aerosols play an important role in climate and air quality. However, up to now, their sources and chemical reaction processes have not been fully understood. Three-dimensional excitation-emission matrix (EEM) method is a direct and effective way to identify the types and sources of the complex atmospheric chromophores, which can also be used to study the chemical reactions involved in the generation and disappearance process. In this study, a PILS-EEM-TOC system (a Particle-Into-Liquid-Sampler coupled with the EEM spectroscopy and a total organic carbon analyzer) was successfully developed for the first time. The results showed that this system can provide the transient dynamic trend of types and concentrations of the water-soluble chromophores in ambient particulate matter (PM) with a time-resolution of up to 15 min. By comparing the PM samples collected by the filter method, the result suggests that the online analysis of the chromophores by the PILS-EEM-TOC system is comparable to the offline filter method. In this case of Xi'an, China, the primary emission and secondary processes of the atmospheric chromophores were observed, the obvious effects of sandstorm-precipitation processes on the types and concentrations of chromophores were also found. The result suggests that a type of highly-oxygenated HULIS chromophores can be used as a secondary source tracer, and a type of less-oxygenated HULIS chromophores can be used as dust source tracer. The PILS-EEM-TOC system has great potential application in a wider spatiotemporal scope to explore the origin, generation and disappearance mechanisms of atmospheric chromophores.