Complex sentence: Despite lessened emissions in the city, smog remains a possibility as warm temperatures allow for pollutants to react in the atmosphere more quickly, this leads to the possibility of high ozone levels despite the drop in pollutants which commonly lead to the production of ozone.
Split into simpler sentences: Despite lessened emissions in the city, smog remains a possibility as warm temperatures allow for pollutants to react in the atmosphere more quickly. This leads to the possibility of high ozone levels despite the drop in pollutants which commonly lead to the production of ozone.