## 3 Results and Discussions
### Temporal Variations and Comparison of m/z 44 Signal with COO of Total Carboxylic Acids  
Figure 3 shows the temporal variations in OM\({}_{\text{AMS}}\) and m/z 44 (COO\({}^{+}\)) signals. The real-time variations in OM\({}_{\text{AMS}}\) and m/z 44 can be found in Figure S1. We found a very strong correlation between OM\({}_{\text{AMS}}\) and m/z 44 signal (R = 0.98). Figure 4 shows the temporal variations in the estimated COO for selected carboxylic acids together with AMS m/z 44 signals. C\({}_{2}\)-C\({}_{4}\) diacids \(\omega\)C\({}_{2}\), \(\omega\)C\({}_{4}\), and \(\omega\)C\({}_{9}\) are mainly produced by the photochemical oxidation of various organic precursors during long-range atmospheric transport to Okinawa (28,49). The temporal variations in COO calculated for total carboxylic acids are similar to those of m/z 44. The m/z 44 signals mainly originate from oxygenated organics [(39; 42)]. Although the /z 44 peak is the largest in AMS mass spectrum, C\({}_{3}\)H\({}_{8}\)\({}^{+}\) and C\({}_{2}\)H\({}_{4}\)O\({}^{+}\) may also contribute to the m/z 44 signals [(41)]. Some amino compounds may produce significant peaks at m/z 44 (C\({}_{2}\)H\({}_{6}\)N\({}^{+}\)) and m/z 28 (CH\({}_{2}\)N\({}^{+}\)). However, these compounds are unlikely to have contributed to those signals in this study because the mass spectra do not show the presence of C\({}_{n}\)H\({}_{2n+1}\)NH\({}^{+}\) ion series, which are characteristic of alkylamines [(54; 42)]. Figure 3: Temporal variations in organics and m/z 44 (COO\({}^{+}\)) signal measured by AMS in aerosols samples collected from Okinawa. Figure 2: Averaged relative abundances of total diacids, total oxoacids (\(\omega\)C\({}_{2}\)-\(\omega\)C\({}_{9}\) and pyruvate acid), benzoic acid, and fatty acids (C\({}_{7}\)-C\({}_{20}\)) in total carboxylic acids detected in the Cape Hedo aerosols (PM\({}_{1,0}\)). Figure 4: Temporal variations in the COO of selected carboxylic acids obtained by GC/FID and m/z 44 (COO\({}^{+}\)) signal obtained by AMS (**a**) oxalic acid (C\({}_{2}\)), (**b**) malonic acid (C\({}_{3}\)), (**c**) succinidic acid (C\({}_{4}\)), (**d**) 4\(-\)ketopimelic acid (kC\({}_{7}\)), (**e**) glyoxylic acid (\(\omega\)C\({}_{2}\)), (**f**) 4\(-\)oxobutanoic acid (\(\omega\)C\({}_{4}\)), (**g**) 9\(-\)oxonanoic acid (\(\omega\)C\({}_{9}\)), (**h**) pyrvvic acid (Pyr), (**i**) benzoic acid (Bez), and (**j**) C\({}_{14\oplus}\) fatty acid. We found strong correlations between m/z 44 signals and the COO of carboxylic acids such as C\({}_{2}\) (R = 0.87), C\({}_{3}\) (0.95), C\({}_{4}\) (0.91), kC\({}_{7}\) (0.90), \(\omega\)C\({}_{2}\) (0.87), \(\omega\)C\({}_{4}\) (0.73), \(\omega\)C\({}_{9}\) (0.93), benzoic acid (0.66), and C\({}_{14:0}\) fatty acid (0.81) (Figure 4). These carboxylic acids contribute to OOA, as presented by AMS m/z 44 in the aerosols [40; 45; 57; 58]. Except for C\({}_{130}\) fatty acid (R = 0.84), the correlation of m/z 44 with other fatty acids is not as good as that of C\({}_{14:0}\). Figure 5 shows temporal variations in the calculated COO for total diacids, oxoacids, benzoic acid, and total fatty acids obtained by GC and AMS-derived m/z 44. The temporal variations in COO are very similar to those of m/z 44 within the accuracy of the methods. For the calculation of COO, we corrected the concentrations of diacids and related compounds using their recoveries (e.g., 90% for oxalic acid). Some difference (e.g., 7 April, Figure 5) may suggest the presence of unidentified organic acids such as formic, acetic, and propanoic acids that have not been determined by the GC method used. The measurements of the two approaches suggest that GC and AMS techniques are important methods to measure carboxylic acids in aged aerosols (PM\({}_{1.0}\)). The higher concentrations of AMS m/z 44 than COO from GC/FID suggest the presence of other organic acids that were not measured by this GC method.