Response of an aerosol mass spectrometer to organonitrates and organosulfates and implications for atmospheric chemistry

Abstract

Organonitrates (ON) are important products of gas-phase oxidation of volatile organic compounds in the troposphere; some models predict, and laboratory studies show, the formation of large, multifunctional ON with vapor pressures low enough to partition to the particle phase. Organosulfates (OS) have also been recently detected in secondary organic aerosol. Despite their potential importance, ON and OS remain a nearly unexplored aspect of atmospheric chemistry because few studies have quantified particulate ON or OS in ambient air. We report the response of a high-resolution time-of-flight aerosol mass spectrometer (AMS) to aerosol ON and OS standards and mixtures. We quantify the potentially substantial underestimation of organic aerosol O/C, commonly used as a metric for aging, and N/C. Most of the ONnitrogen appears as NO þ x ions in the AMS, which are typically dominated by inorganic nitrate. Minor organonitrogen ions are observed although their identity and intensity vary between standards. We evaluate the potential for using NO þ x fragment ratios, organonitrogen ions, HNO þ 3 ions, the ammonium balance of the nominally inorganic ions, and comparison to ion-chromatography instruments to constrain the concentrations of ON for ambient datasets, and apply these techniques to a field study in Riverside, CA. OS manifests as separate organic and sulfate components in the AMS with minimal organosulfur fragments and little difference in fragmentation from inorganic sulfate. The low thermal stability of ON and OS likely causes similar detection difficulties for other aerosol mass spectrometers using vaporization and/or ionization techniques with similar or larger energy, which has likely led to an underappreciation of these species.atmospheric chemistry | organic aerosol | organic nitrate | organic sulfate | SOA O rganonitrates (ON, i.e., RONO 2 ) and organosulfates (OS, i.e., ROSO 3 H) are known to be present in secondary organic aerosol (SOA) (1-4), and are a nearly unexplored but potentially important aspect of atmospheric chemistry. The mechanisms behind ON and OS production and aging are poorly understood and generally ignored in models due in part to a lack of measurement approaches. ON have recently been identified as significant components (15-35%) of NO y in the gas-phase (5, 6) and serve as indicators of ozone production (7). Oceans and certain industrial processes directly emit ON, but these are generally short-chain alkyl nitrates that exist only in the gas-phase and constitute a minor fraction of atmospheric ON (6,8). Most atmospheric ON are produced either by photochemical (OH-initiated) or nocturnal (NO 3 -initiated) oxidation reactions of anthropogenic and biogenic volatile organic compounds (VOCs). These reactions can produce large, multifunctional ON with vapor pressures potentially low enough to condense and form SOA. During photochemical oxidation of VOCs in the presence of nitrogen oxides, ON are minor products of peroxy radical ðRO 2 Þ þ NO reactions. These reactions produce ON with yields of ...

Real Time In Situ Detection of Organic Nitrates in Atmospheric Aerosols

“…(2)(3)(4)(5)(6)) and chemical ionization mass spectrometry (7)(8)(9), and the total of gas and aerosol RONO 2 (total Alkyl Nitrates, ΣAN) has been observed by Thermal Dissociation Laser Induced Fluorescence (TD-LIF) (1,(10)(11)(12). Recently there has been growing interest in understanding the partitioning of RONO 2 to atmospheric particles (13)(14)(15)(16)(17)(18). RONO 2 molecules with 2 -4 functional groups and a carbon backbone of ≥ C 4 have low enough vapor pressures to condense under ambient conditions and mechanistic studies show that RONO 2 can be among the most important molecules to SOA formation (e.g.…”

“…However the most widely used methods for aerosol chemical characterization including Aerosol Mass Spectrometry (AMS) have had limited success. The difficulty of distinguishing inorganic and organic nitrates using AMS has been recently discussed in the literature (16)(17)(18). Nitrates have not yet been reported by Thermal Desorption Aerosol Gas-Chromatography (TAG) (25) or other methods of detailed realtime aerosol characterization.…”

Aircraft-based observations of isoprene epoxydiol-derived secondary organic aerosol (IEPOX-SOA) in the tropical upper troposphere over the Amazon region

“…Laboratory studies demonstrate that around 50 % of isoprene-derived particulate matter is associated with IEPOX production and uptake through the HO 2 pathway and in the presence of acidic aerosol particles (Liu et al, 2015). The existence of aerosol as seed particles seems to be necessary (Surratt et al, 2010;Lin et al, 2012), but also the 25 acidity of aerosol can influence the formation yield of IEPOX-SOA. Laboratory and field studies found a correlation between IEPOX-SOA and sulfate, which is related to the acidity of aerosol (Surratt et al, 2007;Budisulistiorini et al, 2013).…”

“…Further oxidation of ISOPOOH may lead to isoprene epoxydiols (IEPOX), which then can partition into the particle phase by condensation or 20 reactive uptake and, thus, SOA derived from IEPOX (IEPOX-SOA) can be formed (e.g., Claeys et al, 2004;Carlton et al, 2009;Paulot et al, 2009;Surratt et al, 2010;Lin et al, 2012;Budisulistiorini et al, 2013;Worton et al, 2013;St. Clair et al, 2016;Liu et al, 2016b).…”

“…Many studies reported on the difficulties to measure organic 10 nitrates quantitatively, but suggested also a possibility to estimate the amount or at least the presence of organic nitrates based on the measured ion ratios of NO + to NO + 2 using aerosol mass spectrometry (e.g., Bruns et al, 2010;Farmer et al, 2010;Rollins et al, 2010;Fry et al, 2013;Ayres et al, 2015;Kiendler-Scharr et al, 2016;Ng et al, 2017;Schneider et al, 2017).…”