Diurnal variations of gaseous and particulate nitrophenol isomers in the atmosphere monitored by using wet scrubbing online preconcentration

Abstract

Nitrophenols (NPs) are present in the atmosphere in both gas and particle phases. NP isomers differ in their arrangement of hydroxy and nitro groups and additional functional groups. The positively charged hydroxy groups and negatively charged nitro groups affect the characteristics and behaviors of NPs in the atmosphere. In this study, an automated sampler/preconcentrator was developed to monitor variations in ortho- and para-NPs over time in the gas and particle phases separately. A parallel plate wet denuder containing a pair of glass plates and spraying particle extractor were used for collecting gaseous and particulate NPs, respectively. Automated solid-phase extraction preconcentration was performed simultaneously with air sampling. The obtained extracts were analyzed by high-performance liquid chromatography coupled with atmospheric pressure chemical ionization-tandem mass spectrometry (HPLC-APCI-MS/MS). The sampling, preconcentration, and HPLC-APCI-MS/MS methods were optimized. Atmospheric monitoring was performed in winter and evaluation of diurnal variations of NP concentrations showed that they increased at night. NPs were present mostly in the gas phase and concentrations of ortho-NPs were higher than those of para-NPs in the atmosphere. Gaseous 2-nitro-o-cresol was detected for the first time as one of the major NPs in winter. The particulate fractions of NPs increased at night and the maximum fractions were observed in the morning. Para-NPs were more located in the particulate fraction, and the fraction of 4-nitrophenol (a para-NP) was about double that of 2-nitrophenol (an ortho-NP).