Abstract

The sunlight photochemistry of the organic chromophore pyruvic acid (PA) in water generates ketyl and acetyl radicals that contribute to the production and processing of atmospheric aerosols. The photochemical mechanism is highly sensitive to dissolved oxygen content, [O2(aq)], among other environmental conditions. Thus, herein we investigate the photolysis (λ ≥ 305 nm) of 10–200 mM PA at pH 1.0 in water covering the relevant range 0 ≤ [O2(aq)] ≤ 1.3 mM. The rapid consumption of dissolved oxygen by the intermediate photolytic radicals is monitored in real time with a dissolved oxygen electrode. In addition, the rate of O2(aq) consumption is studied at air flow rates from 30.0 to 900.0 mL min−1. For the range of [PA]0 covered under air saturated conditions and 30 mL min−1 flow of air in this setup, the estimated half-lives of O2(aq) consumed by the photolytic radicals fall within the interval from 22 to 3 min. Therefore, the corresponding depths of penetration of O2(g) into water (x = 4.3 and 1.6 µm) are determined, suggesting that accumulation and small coarse mode aqueous particles should not be O2-depleted in the presence of sunlight photons impinging this kind of chromophore. These photochemical results are of major tropospheric relevance for understanding the formation and growth of secondary organic aerosol.

Highlights

  • Pyruvic acid (PA, pKa = 2.39) [1] is an abundant component of tropospheric aerosols [2,3,4], and one of the few chromophores capable of undergoing photochemical reactions in water [5,6,7,8,9,10]

  • A subject of major interest has been the use of the photogenerated acetyl and ketyl radicals from from irradiated pyruvic acid (PA) solutions to initiate the processing of other water soluble organic atmospheric irradiated PA solutions to initiate the processing of other water soluble organic atmospheric compounds

  • The oligomerization of methyl vinyl ketone (MVK) [28], an important water-soluble intermediate arising from the atmospheric oxidation of isoprene [29], proceeds in the water-soluble intermediate arising from the atmospheric oxidation of isoprene [29], proceeds in the presence of irradiated aqueous PA

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Summary

Introduction

Pyruvic acid (PA, pKa = 2.39) [1] is an abundant component of tropospheric aerosols [2,3,4], and one of the few chromophores capable of undergoing photochemical reactions in water [5,6,7,8,9,10] It is produced during the atmospheric photooxidative processing of biogenic and anthropogenic emissions [11,12]. 2 (−133 °C), the frozen sample began to release appreciable amounts indicating a unidirectional process proceeded after no more forced close contact of radical pairs was of CO[5].

Initial
Results andpart
25 C under sparging of mM
The presented reaction
Rate dissolved oxygen
TheO experiments in Figureconditions
10–5 Einstein
Experiments
Photochemical Conditions
Conclusions
Full Text
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