Hydroxyl radical-induced formation of highly oxidized organic compounds

Abstract

Explaining the formation of secondary organic aerosol is an intriguing question in atmospheric sciences because of its importance for Earth's radiation budget and the associated effects on health and ecosystems. A breakthrough was recently achieved in the understanding of secondary organic aerosol formation from ozone reactions of biogenic emissions by the rapid formation of highly oxidized multifunctional organic compounds via autoxidation. However, the important daytime hydroxyl radical reactions have been considered to be less important in this process. Here we report measurements on the reaction of hydroxyl radicals with α- and β-pinene applying improved mass spectrometric methods. Our laboratory results prove that the formation of highly oxidized products from hydroxyl radical reactions proceeds with considerably higher yields than previously reported. Field measurements support these findings. Our results allow for a better description of the diurnal behaviour of the highly oxidized product formation and subsequent secondary organic aerosol formation in the atmosphere.

An electrospray chemical ionization source for real-time measurement of atmospheric organic and inorganic vapors

“…The selectivity of I − and NO − 3 toward more oxidized species as suggested here is consistent with the observations in previous studies (Lee et al, 2014;Berndt et al, 2016), which showed that these two reagent ions can have distinct sensitivities to the oxidized species having similar oxygen contents, depending on the identities and locations of the functional groups. It is clear in Fig.…”

“…For example, previous studies using NO − 3 CIMS have reported a very low yield of HOMs from OH oxidation of monoterpene . However, a recent study using acetate CIMS found a significantly higher HOMs yields from the same system (Berndt et al, 2016). The reason for this difference is presumably a lower sensitivity of NO − 3 to HOMs formed in OH oxidation of monoterpene than that of acetate (Berndt et al, 2016).…”

“…However, a recent study using acetate CIMS found a significantly higher HOMs yields from the same system (Berndt et al, 2016). The reason for this difference is presumably a lower sensitivity of NO − 3 to HOMs formed in OH oxidation of monoterpene than that of acetate (Berndt et al, 2016). On the other hand, many atmospheric organic systems consist of a wide range of organic compounds with different functionality and polarity.…”

“…The use of HR-ToF-CIMS has allowed for groundbreaking progress in atmospheric organic chemistry, such as the observation of 3610 Y. Zhao et al: An electrospray chemical ionization source highly oxygenated molecules (HOMs) formed by monoterpene oxidation Jokinen et al, 2015;Berndt et al, 2016;Lee et al, 2016). Very recently, a newly developed proton-transfer reaction (PTR) time-of-flight instrument (PTR-3) has enabled sensitive detection of a wide range of organic compounds including HOMs (Breitenlechner et al, 2017).…”

“…As such, certain reagent ions such as metal cations (e.g., Li + , Na + , and K + ) and NH + 4 , which are commonly used for detection of atmospheric organic compounds in offline techniques like electrospray ionization (ESI)-MS (Nizkorodov et al, 2011;Laskin et al, 2012;Witkowski and Gierczak, 2013), have remained largely unavailable for CIMS (Fujii et al, 2001). Compared to I − , NO − 3 , and acetate, which are generally more sensitive to more oxygenated organic compounds than to less oxygenated ones (Aljawhary et al, 2013;Lee et al, 2014;Hyttinen et al, 2015;Iyer et al, 2016;Berndt et al, 2016), these metal cations are expected to be able to sensitively detect both less oxygenated (e.g., compounds containing only carbonyl groups) and highly oxygenated multi-functional organic species (Gao et al, 2010;Nguyen et al, 2010;Nizkorodov et al, 2011;Laskin et al, 2012;Witkowski and Gierczak, 2013;Zhao et al, 2015Zhao et al, , 2016Tu et al, 2016;Zhang et al, 2017), and to form more strongly bound ion adducts. In addition, at present most CIMS techniques use a radioactive ion source such as 210 Po to produce the reagent ions, although more recently some utilize X-ray radiation, electrical discharge (Hirokawa et al, 2009;Yuan et al, 2016), or electron impact (Inomata and Hirokawa, 2017).…”