# Direct Measurement of Aerosol Liquid Water Content: A Case Study in Summer in Nanjing, China
## 3 Results and Discussion
### ALWC Results and Correlations with Other Variables  
Figure 3 shows the meteorological parameters, concentrations of gaseous pollutants, dry PM\({}_{2.5}\) (from 5030i), and ALWC over the measurement period. The averaged diurnal patterns of relevant variables are shown in Figure 4. The campaign-averaged temperature was 31.19 \({}^{\circ}\)C, and the mean RH was 63.42%, indicating hot and mildly humid weather overall. The temperature peaked in the afternoon while the RH was relatively high at night (Figure 4a,b). The wind was often from the southeast (with an average of 148.6\({}^{\circ}\)). Its speed was low (an average of 1.11 m s\({}^{-1}\) and a maximum of 3.22 m s\({}^{-1}\)) and it was particularly weak at night (\(\sim\)0.75 m s\({}^{-1}\)), coinciding with a high RH. This indicates that stagnant and humid air conditions therefore were unfavorable for pollutant dispersion. Figure 4: Diurnal variations in (**a**) Temperature, (**b**) RH, (**c**) WS, and concentrations of (**d**) NO\({}_{2}\), (**e**) CO, (**f**) PM\({}_{2.5}\), (**g**) SO\({}_{2}\), (**h**) O\({}_{3}\), and (**i**) ALWC. The SO\({}_{2}\), NO\({}_{2}\), O\({}_{3}\), and CO concentrations were averaged to be 5.76, 16.64, 94.56 ug m\({}^{-3}\), and 0.53 mg m\({}^{-3}\), respectively. The daily variations in SO\({}_{2}\) and CO are quite similar (Figure 4g,e), likely indicating their similar sources from the nearby industrial area. The daily NO\({}_{2}\) pattern was a bit different as it remained high after midnight (Figure 4d). The daily trends of O\({}_{3}\) were opposite to those of NO\({}_{2}\) (Figure 4h), reflecting the consumption of NO\({}_{2}\) to produce O\({}_{3}\)[45]. The average PM\({}_{2.5}\) mass loading was 19.50 ug m\({}^{-3}\), ranging from 1.87 ug m\({}^{-3}\) to 68.65 ug m\({}^{-3}\). On a daily basis (Figure 4f), the PM\({}_{2.5}\) concentration peaked in the morning (24.60 ug m\({}^{-3}\) at ~7:00 am) and reached a minimum of 16.12 ug m\({}^{-3}\) at ~18:00 pm, partially owing to influences from the WS, RH, and variations in planetary boundary layer height. The determined ALWC varied from 0.003 to 23.84 ug m\({}^{-3}\), with an average of 3.85 ug m\({}^{-3}\). The ALWC occupied on average 16.5% of the total aerosol mass (23.35 ug m\({}^{-3}\)). The visibility varied from 0.51 to 30 km, with a campaign mean of 14.37 km. The temporal trends of the ALWC and visibility are the opposite of one another as illustrated in Figure 3f, demonstrating the significant role of ALWC in visibility degradation (see our further discussion in Section 3.4). The diurnal trend of the ALWC (Figure 4i) naturally resembled that of the RH (Figure 4b); it peaked at ~6:00 am (7.88 ug m\({}^{-3}\)), reached the lowest value at 15:00 pm (0.90 ug m\({}^{-3}\)), and then began to rise in line with the increase in RH and decrease in temperature (Figure 4a,b), which favored the partitioning/condensation of water vapor onto particles [23; 26]. Figure 5 further presents the cross-correlation coefficients among the temporal variations in the measured variables. The ALWC correlated positively with the RH (r of 0.60) and PM\({}_{2.5}\) (0.60) as expected, but negatively with the WS (\(-\)0.42) and T (\(-\)0.48) as well as O\({}_{3}\) (\(-\)0.34). The results show clearly that the PM\({}_{2.5}\) concentration and RH govern the ALWC, while high temperatures and winds accompanied by high O\({}_{3}\) values on the contrary promoted the evaporation of the ALWC into the gas phase. The visibility mainly showed positive correlations with the WS (r of 0.48) and T (0.28), indicating that the visibility is great in hot weather with high wind speeds. However, the visibility was negatively correlated with the ALWC (r of \(-\)0.57), RH (\(-\)0.54), and PM\({}_{2.5}\) (\(-\)0.45), indicating heavy impacts from the ALWC and PM\({}_{2.5}\) loadings. Figure 5: Cross-correlation coefficients (Pearson’s r) among gaseous pollutants (NO\({}_{2}\), CO, SO\({}_{2}\), O\({}_{3}\)), RH, T, WS, ALWC, and visibility.