Articles | Volume 17, issue 22
https://doi.org/10.5194/acp-17-13891-2017
https://doi.org/10.5194/acp-17-13891-2017
Research article
 | 
22 Nov 2017
Research article |  | 22 Nov 2017

Insight into the in-cloud formation of oxalate based on in situ measurement by single particle mass spectrometry

Guohua Zhang, Qinhao Lin, Long Peng, Yuxiang Yang, Yuzhen Fu, Xinhui Bi, Mei Li, Duohong Chen, Jianxin Chen, Zhang Cai, Xinming Wang, Ping'an Peng, Guoying Sheng, and Zhen Zhou

Abstract. While ground-based works suggest the significance of in-cloud production (or aqueous formation) to oxalate, direct evidence is rare. With the in situ measurements performed at a remote mountain site (1690 m above sea level) in southern China, we first reported the size-resolved mixing state of oxalate in the cloud droplet residual (cloud RES), the cloud interstitial (cloud INT), and ambient (cloud-free) particles by single particle mass spectrometry. The results support the growing evidence that in-cloud aqueous reactions promote the formation of oxalate, with  ∼  15 % of the cloud RES and cloud INT particles containing oxalate in contrast to only  ∼  5 % of the cloud-free particles. Furthermore, individual particle analysis provides unique insight into the formation of oxalate during in-cloud processing. Oxalate was predominantly (> 70 % in number) internally mixed with the aged biomass-burning particles, highlighting the impact of biomass burning on the formation of oxalate. In contrast, oxalate was underrepresented in aged elemental carbon particles, although they represented the largest fraction of the detected particles. It can be interpreted by the individual particle mixing state that the aged biomass-burning particles contained an abundance of organic components serving as precursors for oxalate. Through the analysis of the relationship between oxalate and organic acids (−45[HCO2], −59[CH3CO2], −71[C2H3CO2], −73[C2HO3]), the results show that in-cloud aqueous reactions dramatically improved the conversion of organic acids to oxalate. The abundance of glyoxylate associated with the aged biomass-burning particles is a controlling factor for the in-cloud production of oxalate. Since only limited information on oxalate is available in the free troposphere, the results also provide an important reference for future understanding of the abundance, evolution, and climate impacts of oxalate.

Short summary
We first reported the size-resolved mixing state of oxalate in the cloud droplet residual, the cloud interstitial, and cloud-free particles by single particle mass spectrometry. Individual particle analysis provides unique insight into the formation and evolution of oxalate during in-cloud processing. The data show that in-cloud aqueous reactions dramatically improved the formation of oxalate from organic acids that were strongly associated with the aged biomass burning particles.
Altmetrics
Final-revised paper
Preprint