## 3 Results and Discussion  
### Average Seasonal Variations of VOCs  
Significant seasonal variations (one-way ANOVA, Tukey test, \(p<0.01\)) were observed for 9 out of 19 VOCs (Figure 2). However, those 9 VOCs (benzene, propylbenzene, benzaldehyde, 3-picoline, naphthalene, fluorene, methylene chloride, \(n\)-decane, and \(n\)-heptane) resulted in a non-significant or low correlation with humidity and precipitation (Table S3 in Supplementary Materials). The pollutants correlated negatively with temperature and positively with pressure except for benzaldehyde, which exhibited a reverse trend. The increasing benzaldehyde level by 5 times in sampling days in summer compared to winter can be caused by higher photochemical activity in that season, leading to secondary carbonyl compounds. Similar seasonal variations were obtained by [PERSON] et al. [32], who proposed that the primary source of benzaldehyde is vehicle emissions. The concentrations of \(n\)-heptane, naphthalene, and benzene decreased gradually by 78-90% from winter to summer sampling days and then increased by 2-3 times in sampling days in autumn (Figure 2). Fluorene concentrations were detected in winter and autumn sampling periods, while in spring and summer, concentrations were below LODs. Moreover, in the winter sampling periods, the maximum concentrations of \(n\)-decane (19 \(\mathrm{\SIUnitSymbolMicro m^{-3}}\)) and methylene chloride (47 \(\mathrm{\SIUnitSymbolMicro m^{-3}}\)) were observed. The high levels of the above-mentioned VOCs in sampling periods in winter can be attributed to meteorological conditions of Almaty and specific geographic location [22]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Analyte**} & \multirow{2}{*}{**N \({}^{*}\)**} & \multicolumn{6}{c}{**Concentration, \(\mathrm{\SIUnitSymbolMicro m^{-3}}\)**} \\ \cline{3-8}  & & **Mean** & **SD** & **Minimum** & **Maximum** &
\begin{tabular}{c} **WHO** \\ **(24-h Limit)** \\ \end{tabular} \\ \hline \(\mathrm{NO_{2}}\) & 81 & 81 & 68 & 0.10 & 436 & 25 \\ \(\mathrm{PM_{2.5}}\) & 92 & 44 & 49 & 2.00 & 260 & 15 \\ \(\mathrm{SO_{2}}\) & 67 & 8.4 & 8.5 & 0.10 & 36 & 40 \\ \(\mathrm{CO}\), \(\mathrm{mg}\)\(\mathrm{m}^{-3}\) & 69 & 1.2 & 1.2 & 0.06 & 5.0 & - \\ \hline \hline \end{tabular} \({}^{*}\)Note: N—number of measurements.  
\end{table} 
Table 4: Descriptive statistics of the concentrations of \(\mathrm{NO_{2}}\), \(\mathrm{SO_{2}}\), \(\mathrm{CO}\), and \(\mathrm{PM_{2.5}}\). Figure 2: Seasonal concentrations (mean of the sampling days in each season \(\pm\) SD) of the VOCs. During winter sampling, the mean temperature and pressure were \(-5.7\,^{\circ}\)C and 775 mm Hg, while during sampling in spring, summer, and autumn, it varied from 9.3 to 24.3\(\,{}^{\circ}\)C and from 762 to 768 mm Hg. The highest average wind speed was observed during the sampling period in summer (1.5 m s\({}^{-1}\)); in other seasons' sampling periods, average wind speed ranged from 0.2 to 0.3 m s\({}^{-1}\). [PERSON] et al. [33] proposed that high TVOCs concentrations in the heating season (winter) can be attributed to the decreasing VOCs photodegradation. In addition, high concentrations of VOCs in winter may be associated with poorer dispersion conditions caused by high pressure [34], low planetary boundary layer heights, or the presence of low-level inversion layers. The seasonal variations of toluene, 1,2-dichloroethane, ethylbenzene, \(m\)-, \(p\)-, \(o\)-xylenes, propylbenzene, chlorobenzene, 1,3,5-trimethylbenzene, 1,2,4-trimethylbenzene, and phenol were insignificant and varied from 0.070 to 61 \(\upmu\)g m\({}^{-3}\) (Figure S1 in Supplementary Materials). The mean spring sampling period concentrations of VOCs were calculated as mean concentrations of sampling days in heating (3, 5, 7 April) and non-heating (28, 30 April, and 3 May) periods. Above-mentioned periods were chosen for sampling in spring for evaluation effect of the heating season, which ended a week before sampling on 28 April.