*3.1. Species Composition Characteristics of VOCs*

During the sampling period, 58 VOC compounds (alkanes, olefins, and aromatic hydrocarbons) were detected in the atmosphere at the urban and suburban monitoring sites in Jinghong, and a total of 48 VOC species were detected. As shown in Table 1, the total concentration of VOCs was (144.34 ± 36.15) μg·m−<sup>3</sup> at the urban sampling site, which was much higher than at the suburban sampling site (48.21 ± 12.55 μg·m<sup>−</sup>3). Compared with the suburban sampling site, the urban sampling site in Jinghong was closer to various anthropogenic emission sources, which are susceptible to factors such as the emission of VOC sources of human activities. These emission sources have the characteristics of continuity, concentration, and high concentration, which make the concentration of VOCs in urban areas highly accumulated. As shown in Figure 2, in the dry season, the concentrations of alkanes, olefins, aromatic hydrocarbons, and TVOCs in the urban areas of Jinghong were (69.94 ± 9.25) μg·m<sup>−</sup>3, (37.53 ± 8.22) μg·m<sup>−</sup>3, (38.72 ± 17.32) μg·m<sup>−</sup>3, and 146.19 μg·m<sup>−</sup>3, respectively, with those in the suburban areas were (7.40 ± 2.34) μg·m<sup>−</sup>3, (32.22 ± 7.99) μg·m<sup>−</sup>3, (6.74 ± 3.43) μg·m<sup>−</sup>3, and TVOCs 47.15 μg·m<sup>−</sup>3, respectively. During the rainy season, the concentrations of alkanes, olefins, aromatic hydrocarbons, and TVOCs in urban areas were (62.93 ± 16.13) μg·m<sup>−</sup>3, (33.44 ± 8.22) μg·m<sup>−</sup>3, (46.13 ± 13.17) μg·m<sup>−</sup>3, and 142.5 μg·m<sup>−</sup>3, respectively, and those in suburban areas were (6.21 ± 1.99) μg·m<sup>−</sup>3, (37.48 ± 6.69) μg·m<sup>−</sup>3, (5.58 ± 2.65) μg·m<sup>−</sup>3, and 49.27 μg·m<sup>−</sup>3, respectively. The VOC groups at the urban sampling site were mainly alkanes, while the VOC groups at the suburban sampling site were mainly olefins. A nonparametric test (one-way analysis of variance, 95% confidence level) showed there were no significant differences in VOCs concentration and species composition between the dry season and rainy season (*p* > 0.05). The concentration of aromatic hydrocarbon groups in the urban sampling site was higher than that in the dry season, which may be related to the increase in benzene emissions due to the cooling of motor vehicle air conditioning and cooling in the rainy season.


**Table 1.** Concentration levels of atmospheric VOCs in different cities.

**Figure 2.** Concentration of alkanes, olefins, and aromatics in urban and suburban areas of Jinghong.

The comparison of VOC species concentrations in different atmospheric environments in Jinghong and other cities is shown in Table 1. The data sample collection equipment used a Suma tank with a volume of 6 L, and about 28 effective samples were in Kunming. The samples were collected with stainless-steel tubes, and about 12 effective samples were collected in Chengdu. VOC observations adopted syntech spectra gc955 online monitoring systems produced by synspec company in the Netherlands, and about 220 groups of effective data were from Guangzhou. The VOC sampling was conducted at the superstation for atmospheric environmental monitoring in Beijing Normal University, and the amount of valid data was not mentioned in Beijing. Samples were collected using ENTECH (Malvern, PA, USA) summa electro-polished stainless-steels container (6 L) following the United States Environmental Protection Agency analytical method (US EPA, 1999), and about 56 effective samples were collected in Monterey; an automatic measurement system for Non-methane Hydrocarbons (NMHCs) was constructed. The system was set-up at the Hydrospheric Atmospheric Research Center (HyARC) building in Nagoya University, and the amount of valid data was not mentioned in Nagoya (Japan). The sampling areas of the above cities were urban areas. Table 1 shows that there was a significant difference in the proportion of species between the urban and suburban area of Jinghong City. The concentration in the urban area was about three times that in the suburbs. The highest proportion of VOC species in the urban area was alkane, 46.03%, followed by olefin and aromatic hydrocarbon species, accounting for 24.58% and 29.39%, respectively. Its species composition was different from those of Kunming, Guangzhou, Beijing, Chengdu, Monterrey, Nagoya, and other cities. The proportion of olefins in the suburbs of Jinghong was highest (73.11%), followed by alkanes and aromatic hydrocarbons (14.12% and 12.78%, respectively), which may be related to the dense vegetation in the suburbs monitored by this study. During the whole observation period, the average concentration of VOCs in the

urban area of Jinghong city reached (144.35 ± 36.15) μg·m<sup>−</sup>3, which was higher than those in other comparison cities, showing a high concentration level.

Figure 3 shows the distribution of VOC species concentrations in the dry and rainy seasons of the urban and suburban sampling site in Jinghong during the sampling period. As shown in Figure 2, the propane concentrations at the urban sampling site were highest during the entire sampling period. Higher alkane concentrations included propane, nbutane, isobutane, and isoamylene; alkene concentrations included isoprene and propylene species. Higher aromatic hydrocarbon concentrations were mainly toluene, which was much higher than the concentration of suburban points, reflecting the more significant impact of urban motor vehicle exhaust on the concentration of atmospheric VOCs. The concentration of isoprene in the suburban monitoring points was more prominent, which is closely related to suburban monitoring sites moving away from anthropogenic sources and closer to natural sources such as dense forests. This was followed by propane, probably related to petrochemical emissions. The concentrations of other species were low. The spectral characteristics of VOCs at the two sampling sites in Jinghong urban and suburban areas had a large difference, indicating that there were certain differences in the sources of VOCs between the two sampling sites in the city and suburb.

**Figure 3.** The level profiles of VOCs concentrations in Jinghong.
