The dihydroxycarbonyls 3,4-dihydroxy-2-butanone (DHBO) and 2,3-dihydroxy-2-methylpropanal (DHMP) formed from isoprene oxidation products in the atmospheric gas phase under low-NO conditions can be expected to form aqSOA in the tropospheric aqueous phase because of their solubility. In the present study, DHBO and DHMP were investigated concerning their radical-driven aqueous-phase oxidation reaction kinetics. For DHBO and DHMP the following rate constants at 298 K are reported: k(OH + DHBO) = (1.0 ± 0.1) × 10 L mol s, k(NO + DHBO) = (2.6 ± 1.6) × 10 L mol s, k(SO+ DHBO) = (2.3 ± 0.2) × 10 L mol s, k(OH + DHMP) = (1.2 ± 0.1) × 10 L mol s, k (NO + DHMP) = (7.9 ± 0.7) × 10 L mol s, k(SO + DHMP) = (3.3 ± 0.2) × 10 L mol s, together with their respective temperature dependences. The product studies of both DHBO and DHMP revealed hydroxydicarbonyls, short chain carbonyls, and carboxylic acids, such as hydroxyacetone, methylglyoxal, and lactic and pyruvic acid as oxidation products with single yields up to 25%. The achieved carbon balance was 75% for DHBO and 67% for DHMP. An aqueous-phase oxidation scheme for both DHBO and DHMP was developed on the basis of the experimental findings to show their potential to contribute to the aqSOA formation. It can be expected that the main contribution to aqSOA occurs via acid formation while other short-chain oxidation products are expected to back-partition into the gas phase to undergo further oxidation there.

During haze periods in the North China Plain, extremely high NO concentrations have been observed, commonly exceeding 1 ppbv, preventing the classical gas-phase H 2 O 2 formation through HO 2 recombination. Surprisingly, H 2 O 2 mixing ratios of about 1 ppbv were observed repeatedly in winter 2017. Combined field observations and chamber experiments reveal a photochemical in-particle formation of H 2 O 2 , driven by transition metal ions (TMIs) and humic-like substances (HULIS). In chamber experiments, steady-state H 2 O 2 mixing ratios of 116 ± 83 pptv were observed upon the irradiation of TMI-and HULIS-containing particles. Correspondingly, H 2 O 2 formation rates of about 0.2 ppbv h −1 during the initial irradiation periods are consistent with the H 2 O 2 rates observed in the field. A novel chemical mechanism was developed explaining the in-particle H 2 O 2 formation through a sequence of elementary photochemical reactions involving HULIS and TMIs. Dedicated box model studies of measurement periods with relative humidity >50% and PM 2.5 ≥ 75 μg m −3 agree with the observed H 2 O 2 concentrations and time courses. The modeling results suggest about 90% of the particulate sulfate to be produced from the SO 2 reaction with OH and HSO 3 − oxidation by H 2 O 2 . Overall, under high pollution, the H 2 O 2 -caused sulfate formation rate is above 250 ng m −3 h −1 , contributing to the sulfate formation by more than 70%.

Atmospheric nitrophenols are pollutants of concern due to their toxicity and light-absorption characteristics and their low reactivity resulting in relatively long residence times in the environment. We investigate multiphase nitrophenol formation from guaiacol in a simulated atmospheric aerosol and support observations with the corresponding chemical mechanisms. The maximal secondary organic aerosol (SOA) yield (42%) is obtained under illumination at 80% relative humidity. Among the identified nitrophenols, 4-nitrocatechol (3.6% yield) is the prevailing species in the particulate phase. The results point to the role of water in catechol and further 4-nitrocatechol formation from guaiacol. In addition, a new pathway of dark nitrophenol formation is suggested, which prevailed in dry air and roughly yielded 1% nitroguaiacols. Furthermore, the proposed mechanism possibly leads to oligomer formation via a phenoxy radical formation by oxidation with HONO.

A substantial fraction of sub-micron tropospheric aerosol particles (20%-90%) consists of organic matter (Jimenez et al., 2009;Q. Zhang et al., 2007). Its formation can be attributed to either direct emission of primary organic aerosol or to reactions of organic compounds in the gas phase followed by condensation and chemical processing leading to secondary organic aerosol (SOA;Ervens et al., 2011). Currently, the total global SOA burden is modeled to range from 0.3 to 2.3 Tg (

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.