Indoor heterogeneous photochemistry of furfural drives emissions of nitrous acid

Abstract

People spend approximately 80% of their time indoor, making the understanding of the indoor chemistry an important task for safety. The high surface-area-to-volume ratio characteristic of indoor environments leads the semi-volatile organic compounds (sVOCs) to deposit on the surfaces. Using a long path absorption photometer (LOPAP), this work investigates the formation of nitrous acid (HONO) through the photochemistry of adsorbed nitrate anions and its enhancement by the presence of furfural. Using a high-resolution proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS), this work also investigates the surface emissions of VOCs from irradiated films of furfural and a mix of furfural and nitrate anions. Among the emitted VOCs, 2(5H)-furanone/2-Butenedial was observed at high concentrations, leading to maleic anhydride formation after UV irradiation. Moreover, the addition of potassium nitrate to the film formed NO x and HONO concentrations up to 10 ppb, which scales to ca. 4 ppb for realistic indoor conditions. This work helps to understand the high levels of HONO and NO x measured indoors.

Indoor heterogeneous photochemistry of molds and their contribution to HONO formation

“…Hence, indoor surfaces covered with molds can be a non‐negligible source of HONO mainly in sick buildings exhibiting large, contaminated areas, alongside high relative humidity, and low ventilation rates. Typical indoor levels are of the order of few ppbs 28,29,32 . These levels could significantly be affected by surface chemistry as it was previously demonstrated for various indoor surfaces 29,32,76 and for microbial indoor surface in the present work.…”

“…The mass spectrometry analysis of the mixed solution of molds extract and potassium nitrate showed the formation of some nitro and nitrogenated compounds during the film preparation. Depoorter et al 32 have also shown a possible nitration reaction during the preparation of furfural and potassium nitrate films. The authors have proposed a mechanism for the photochemical degradation of 2‐nitrofuran (a proxy for nitro compounds formed during the preparation of furfural films doped with KNO 3 ).…”

“…In fact, the wavelengths of the LED lamp used in this study ranged between 335 and 380 nm. Thus, at these wavelengths, the photochemistry of potassium nitrate cannot be activated efficiently because due to a low absorption beyond 335 nm 32 …”

“…It was demonstrated by Depoorter et al 32 that a possible reaction may occur between nitrate anions and reactive organic compounds during the drying process of a wet film, resulting in the formation of nitro groups. Therefore, we characterized the potential formation of nitrogenated compounds in a mixed solution of molds extract and potassium nitrate using a direct infusion in an Orbitrap high‐resolution mass spectrometer (HRMS, Q Exactive, Thermo Scientific, Bremen, Germany) with a heated electrospray ionization (ESI).…”

“…It can also form carcinogenic nitrosamines via its reaction with secondary amines 28 . Several studies have shown that the HONO formation can be enhanced by light (300 nm < λ < 400 nm) 7,27,28,32,35 . Besides, nitrate anions can result from the oxidation of NO x into nitric acid (HNO 3 ).…”