*3.2. Ozone Formation Potentials (OFP) of VOCs*

Table 2 lists the OFP values of VOCs species at urban and suburban sampling sites in Jinghong. The OFP of total VOCs in the atmosphere in the urban area of Jinghong was 588.07 μg·m−<sup>3</sup> and 535.38 μg·m−<sup>3</sup> in the dry season and 535.38 μg·m<sup>−</sup>3, respectively, which was much higher than that of the suburb, indicating that the ozone generation capacity in the urban area of Jinghong was much higher than that in the suburban area. In the dry season, urban alkanes, olefins, and aromatic hydrocarbons accounted for 11.49%, 57.73%, and 30.78% of the OFP, respectively, and correspondingly accounted for 1.82%, 89.70%, and 8.48% of the OFP in the suburb. During the rainy season, alkanes, olefins, and aromatic hydrocarbons

accounted for 10.10%, 56.91%, and 32.99% of the OFP in the urban atmosphere, respectively, compared with 1.14%, 92.41%, and 6.45% in the suburb during the same period. Olefins are the key species of ozone formation potential in Jinghong, and the OFP ranking has always been manifested as: olefins > aromatic hydrocarbons > alkanes. The contribution of olefins to ozone generation in the suburban atmosphere is higher than that in urban areas, indicating that the suburban ozone generation is mainly affected by olefins.


**Table 2.** Potential Ozone Formation of VOCs in Jinghong.

DU: Dry season—Urban; DS: Dry season—Suburb; RU: Rainy season—Urban; RS: Rainy season—Suburb.

From the analysis of specific VOCs compounds, in the dry season, the top 12 substances with the highest OFP in the atmosphere of Jinghong were propylene, isoprene, toluene, 1,2,4-trimethylbenzene, p-ethyltoluene, cis-2-butene, o-xylene, 1,2,3-trimethylbenzene, 1-butene, propane, n-butane, and trans-2-butene, and their mass concentration accounts for 67.86% of total volatile organic compounds (TVOCs). The top 12 substances in the suburban area regarding OFPs were isoprene, propylene, cis-2-butene, p-diethylbenzene, 1,2,4-trimethylbenzene, styrene, p-ethyltoluene, toluene, propane, 1,2,3-trimethylbenzene, o-xylene, and isopentane, which accounted for 88.75% of the TVOCs by mass. The ozone generation accounted for 97.28% of the total OFPs. In the rainy season, the top 12 substances of OFPs in the urban air were isoprene, propylene, toluene, 1,2,4-trimethylbenzene, styrene, cis-2-butene, propane, n-butane, p-ethyltoluene, 1,2,3-trimethylbenzene, ethylbenzene, and isobutane, which accounted for 83.34% of TVOCs by mass and 88.26% of total OFP by ozone generation. The top 12 substances of OFPs in the suburb were isoprene, cis-2 butene, styrene, 1,2,4-trimethylbenzene, isopropylbenzene, m-diethylbenzene, propane, propylene, ethylbenzene, toluene, p- and m-xylene, and o-xylene, which accounted for 90.69% of the TVOCs by mass and 97.20% of the total OFPs by ozone potential. Overall, isoprene accounted for the highest percentage of OFP in Jinghong, indicating that natural vegetation emission sources in Jinghong contributed prominently to ozone, followed by toluene, propylene, m-p-xylene, and other motor vehicle exhaust emissions that contributed significantly to ozone generation.
