Photodegradation of 1-nitronaphthalene, 2-nitronaphthalene, and 2-methyl-1-nitronaphthalene in the atmosphere

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous compounds in the atmosphere. These compounds cover a wide range of structures and chemical properties. Among them, nitro derivatives of PAHs (nitro-PAHs) are of particular interest. Nitro-PAHs are formed both by direct emissions, such as from diesel combustion engines, and by secondary reactions, such as nitration of parent PAHs. Furthermore, nitro-PAHs are recognized as toxic pollutants with adverse effects on human health [1], requiring detailed studies of their atmospheric behavior, transformations and effects.

This work focuses on three nitro-PAHs: 1-nitronaphthalene (1NN), 2-nitronaphthalene (2NN) (being these two the most abundant nitro-PAHs in the gas phase [2]), and 2-methyl-1-nitronaphthalene (2M1NN) (frequently detected in diesel exhaust [3]). The photolysis of these compounds was studied in order to understand their degradation pathways and to identify their main reaction products.

Experiments were carried out under sunlight conditions at the outdoor EUropean PHOtoREactor (EUPHORE) in Valencia, Spain.

A comprehensive suite of analytical techniques was employed, including chemical ionization mass spectrometry (CIMS), proton transfer-time of flight-mass spectrometry (PTR-ToF-MS), Fourier transform infrared (FTIR) spectroscopy, scanning mobility particle sizer (SMPS), among others. The main reaction products detected have been certain common acids such as nitrous, formic, acetic, nitric, or lactic acids. These methods provided detailed insights into the chemical transformations and effects of nitro-PAHs under atmospheric conditions, contributing to a better understanding of their environmental and health impacts. In addition, other compounds have been detected, albeit in smaller quantities, due to the partial decomposition of these nitronaphthalenes, such as 1- and 2-napthol, 2-carboxybenzaldehyde, or nitrobenzoic acid. This study sheds light on the nature of these nitronaphthalenes and their reaction mechanism in the atmosphere.

This work is part of a project that is supported by CAPOX RTI2018-097768-B-C21 funded by MCIN and co-funded by ERDF, by ATMOBE PID2022-142366OB-I00 funded by MCIN/AEI/10.13039/501100011033, by “ERDF A way of making Europe”, and by PROMETEO (EVER project) CIPROM/2022/37.

 

References:

[1] Benbrahim-Tallaa, L. et al., Lancet Oncol. 2012, 13, 663.

[2] Albinet, A. et al. Sci. Total Environ. 2007, 384, 280.

[3] Paputa-Peck, M.C. et al. Anal. Chem. 1983, 55, 1946.