Synthesis and Characterization of Atmospherically Relevant Hydroxy Hydroperoxides

Abstract

Hydroxy hydroperoxides are formed upon OH oxidation of volatile organic compounds in the atmosphere and may contribute to secondary organic aerosol growth and aqueous phase chemistry after phase transfer to particles. Although the detection methods for oxidized volatile organic compounds improved much over the past decades, the limited availability of synthetic standards for atmospherically relevant hydroxy hydroperoxides prevented comprehensive investigations for the most part. Here, we present a straightforward improved synthetic access to isoprene-derived hydroxy hydroperoxides, i.e., 1,2‑ISOPOOH and 4,3-ISOPOOH. Furthermore, we present the first successful synthesis of an α-pinene derived hydroxy hydroperoxide. All products were identified by 1H, 13C NMR spectroscopy for structure elucidation, additional 2D NMR experiments were performed. Furthermore, gas-phase FTIR- and UV/VIS spectra are presented for the first time. Using the measured absorption cross section, the atmospheric photolysis rate of up to 2.1 × 10−3 s−1 was calculated for 1,2‑ISOPOOH. Moreover, we present the investigation of synthesized hydroxy hydroperoxides in an aerosol chamber study by online MS techniques, namely PTR-ToFMS and (NO3−)-CI-APi-ToFMS. Fragmentation patterns recorded during these investigations are presented as well. For the (NO3−)-CI-APi-ToFMS, a calibration factor for 1,2‑ISOPOOH was calculated as 4.44 × 10−5 ncps·ppbv−1 and a LOD (3σ, 1 min average) = 0.70 ppbv.

Secondary Organic Aerosol (SOA) through Uptake of Isoprene Hydroxy Hydroperoxides (ISOPOOH) and its Oxidation Products

“…The standard quantification of NO 3 – -CIMS using H 2 SO 4 as a proxy for the cluster stability of HOMs vastly underestimated the ISOPOOH concentration by more than five orders of magnitude (Figure S3). This effect can be attributed to the reduced stability of the resulting ISOPOOH-nitrate cluster. The PTR-ToFMS spectrum showed an increase of methyl-vinyl-ketone (MVK) upon 1,2-ISOPOOH injection, resulting from quantitative decay of 1,2-ISOPOOH, as reported previously .…”

“…See also Section S2 “NO 3 – -CI-APi-ToFMS Calibration” for a more detailed description. Furthermore, a calibration for 1,2-ISOPOOH was performed with the synthetic standard similar to previous studies . To this end, 1,2-ISOPOOH as a viscous liquid was placed in a 50 mL glass flask and flushed with 10 L min –1 purified air into the chamber setup for increasing time periods of 30–300 s. For calibration, the mass loss in the flask was correlated to the signal increase of the corresponding NO 3 – cluster signal.…”

“…A number of characterization experiments were performed with an in-house-synthesized analytical standard of 1-hydroxy-2-hydroperoxy-isoprene (1,2-ISOPOOH) , that was used for the experiments throughout this work. A detailed description of these experiments is given in Section S4 “1,2-ISOPOOH Characterization Experiments” with Table S1 summarizing the experimental conditions.…”

“…Furthermore, a calibration for 1,2-ISOPOOH was performed with the synthetic standard similar to previous studies. 43 To this end, 1,2-ISOPOOH as a viscous liquid was placed in a 50 mL glass flask and flushed with 10 L min −1 purified air into the chamber setup for increasing time periods of 30−300 s. For calibration, the mass loss in the flask was correlated to the signal increase of the corresponding NO 3 − cluster signal. As the NO 3 − -CIMS mode resulted in a comparatively low signal for 1,2-ISOPOOH, n-butylammonium ionization was applied, 27 which showed a much higher sensitivity toward ISOPOOH.…”

Oxidation characteristic and thermal runaway of isoprene

“…Isoprene is asymmetric and multiple isomers can be generated. The initial addition of ·OH can occur on the four conjugated carbon chains of isoprene, forming multiple isoprene hydroxyl hydroperoxides (ISOPOOH) isomers [ 14 – 16 ]. These peroxide isomers are highly reactive and may enhance the complexity of the peroxidation reaction [ 17 , 18 ].…”