In this seminar, I will present new results from three different research directions in our group. First, the chemistry of urban atmospheres is continually changing as motor vehicle emissions have been reduced effectively and other sources of pollutants are becoming dominant. Results from a recent field study in Los Angeles will be presented. Compared with the earlier CalNex study in 2010 at the same location, direct emissions were found to be lower, but oxidation rates were higher and, perhaps as a result, photochemical product concentrations were similar or higher than in 2010. Second, wildfires have become a major driver of urban air quality. An extreme case occurred in December of 2021 in Boulder County, when the Marshall Fire burned over 1,000 homes within hours, in a disaster that is eerily similar to the recent fire in Lahaina on Maui. Results from a field study conducted shortly after the Marshall Fire will be presented, which showed how the air quality effects from the fire lingered for weeks, especially inside homes. Third, the domestic production of oil and gas in the U.S. are near all-time highs due to the use of horizontal drilling and hydraulic fracturing. The emissions of air pollutants and methane from this increased industrial activity have received widespread attention. Results will be presented of our research to constrain nitrogen oxide, volatile organic compounds and methane emissions using satellite data. Enhanced formaldehyde over oil and gas production regions was mostly attributed to secondary formation from the hydrocarbons released from this industrial activity.