Comparison of FTIR and Particle Mass Spectrometry for the Measurement of Particulate Organic Nitrates

Abstract

While multifunctional organic nitrates are formed during the atmospheric oxidation of volatile organic compounds, relatively little is known about their signatures in particle mass spectrometers. High resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS) and FTIR spectroscopy on particles impacted on ZnSe windows were applied to NH(4)NO(3), NaNO(3), and isosorbide 5-mononitrate (IMN) particles, and to secondary organic aerosol (SOA) from NO(3) radical reactions at 22 degrees C and 1 atm in air with alpha- and beta-pinene, 3-carene, limonene, and isoprene. For comparison, single particle laser ablation mass spectra (SPLAT II) were also obtained for IMN and SOA from the alpha-pinene reaction. The mass spectra of all particles exhibit significant intensity at m/z 30, and for the SOA, weak peaks corresponding to various organic fragments containing nitrogen [C(x)H(y)N(z)O(a)](+) were identified using HR-ToF-AMS. The NO(+)/NO(2)(+) ratios from HR-ToF-AMS were 10-15 for IMN and the SOA from the alpha- and beta-pinene, 3-carene, and limonene reactions, approximately 5 for the isoprene reaction, 2.4 for NH(4)NO(3) and 80 for NaNO(3). The N/H ratios from HR-ToF-AMS for the SOA were smaller by a factor of 2 to 4 than the -ONO(2)/C-H ratios measured using FTIR. FTIR has the advantage that it provides identification and quantification of functional groups. The NO(+)/NO(2)(+) ratio from HR-ToF-AMS can indicate organic nitrates if they are present at more than 15-60% of the inorganic nitrate, depending on whether the latter is NH(4)NO(3) or NaNO(3). However, unique identification of specific organic nitrates is not possible with either method.

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

“…Several studies show that qualitative measurements and quantification of organic nitrates are of major interest (e.g., Fry et al, 2009;Bruns et al, 2010;Farmer et al, 2010;Ayres et al, 2015;Kiendler-Scharr et al, 2016;Liu et al, 2017;Schneider et al, 2017). Organic nitrates are decomposed during the evaporation and/or ionisation processes in the C-ToF-AMS and, therefore,…”

“…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).…”

“…For our instrument its value lies between 1.49 and 1.56 with a mean and standard deviation value of 1.52 ± 0.03 and is derived from calibration measurements during the campaign. For organic nitrates the literature presents a range of ratios of NO + to NO + 2 that are higher than the ratio for inorganic nitrates and lie between 5 and 12.5 (e.g., Farmer et al, 2010;Fry et al, 2009Fry et al, , 201120 Rollins et al, 2009;Bruns et al, 2010;Boyd et al, 2015).…”

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.…”