## 4 Conclusions  
We compared the abundances of COO obtained by a capillary GC for carboxylic acids including diacids, oxoacids, benzoic acid, and fatty acids with those of COO\({}^{+}\) (m/z = 44) obtained by Aerodyne AMS for the ambient aerosols (PM\({}_{1.0}\)) from Cape Hedo, Okinawa Island, an outflow region from the Asian continent. We found a strong correlation between the two parameters (i.e., carboxylic acids and AMS m/z 44). Although AMS cannot specify the types of carboxylic acids and their molecular species, this study confirms that AMS m/z 44 signals can be used as a surrogate tracer of atmospheric carboxylic acids whose chemical analyses on molecular levels require lots of work and time. However, the detected carboxylic acids with the predominance of oxalic acid account for ca. 50% of AMS m/z 44 signals. This finding further suggests that, in addition to diacids and related compounds, there are significant amounts of organic acids in the PM\({}_{1.0}\) samples. We suppose that LMW monoacids dominated by formic, acetic, and propanoic acids are the important candidates. We also found higher ratios of OC/EC, m/z 44 (COO\({}^{+}\))/OM\({}_{\text{AMS}}\), and diacid specific-COO/OM\({}_{\text{AMS}}\) in this study, demonstrating that the Cape Hedo aerosols are photochemically highly aged during long-range atmospheric transport from East Asia to the western North Pacific Rim.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app12168017/s1](https://www.mdpi.com/article/10.3390/app12168017/s1)]([https://www.mdpi.com/article/10.3390/app12168017/s1](https://www.mdpi.com/article/10.3390/app12168017/s1)), Figure S1: Real time variations of m/z 44 and organics measured by AMS in aerosols from Cape Hedo Okinawa. Figure S2: 64 vs. 643 for all the OA component from Okinawa. Except for the red filled circle, all data are adopted from [PERSON] et al. (2010). Table SI: AMS inlet relative humidity, inlet temperature, molar ratios of ammonium to sulphate and mass ratios of organics to sulphate during 2005, 2006 and 2008 in Cape Hedo, Okinawa. Table S2: Concentrations of organic and inorganic species measured by different methods during the same study period. Text S1: Introduces the calculation of specific diacid to m/z 44. References [110-112] are cited in the Supplementary Materials.  
Conceptualization, K.K.; methodology, B.K.; software, B.K.; validation, K.K., and B.K.; formal analysis, K.T. and A.T.; investigation, K.K., S.G.A. and B.K.; resources, K.K.; data curation, K.K., and B.K.; writing--original draft preparation, B.K.; writing--review and editing, B.K., and K.K.; visualization, B.K.; supervision, K.K.; project administration, K.K.; funding acquisition, K.K. All authors have read and agreed to the published version of the manuscript.  
This study was in part supported by the Japan Society for the Promotion of Science (JSPS) (Grant-in-Aid Nos. 1920405 and 24221001); the Environment Research and Technology Development Fund (B-0903, 2-1403) from the Ministry of the Environment, Japan; and the JSPS Joint Research Program implemented in association with DFG (JRPs-LEAD with DFG:JPS)/JRP 20181601). Data can be provided upon the request to the corresponding author or BK.  
We thank [PERSON]. [PERSON], [PERSON], and [PERSON] for their help in aerosol sampling at Cape Hedo. We also thank the NOAA Air Resources Laboratory (A.R.L.) for the provision of the HYSPLIT transport model and READY website ([[http://www.arl.noaa.gov/ready.php](http://www.arl.noaa.gov/ready.php)]([http://www.arl.noaa.gov/ready.php](http://www.arl.noaa.gov/ready.php)), accessed on 18 July 2022) used in this study.  
The authors declare no conflict of interest.