jats:sec jats:titleAbstract</jats:title> jats:pAir quality was measured before, during, and after a 4th of July fireworks display in downtown Minneapolis, Minnesota using a mix of low-cost sensors (CO, COjats:sub2</jats:sub>, and NO) for gases and portable moderate cost instruments for particle measurements (PMjats:sub2.5</jats:sub>, lung deposited surface area, and number weighted particle size distributions). Meteorological conditions—temperature, humidity, and vertical temperature profile were also monitored. Concentrations of particles and most gaseous species peak between 10 pm and midnight on July 4th, decrease in the middle of the night but increase again and by between 6 and 7 am reach concentrations as high or higher than during fireworks. This overnight increase is likely due to a temperature inversion trapping emissions. Between 10 pm and midnight on July 4th the measures of particle concentration increase by 180–600% compared to the same period on July 3rd. Particle size distributions are strongly influenced by fireworks, shifting from traffic-like bimodal distributions before to a nearly unimodal distribution dominated by a large accumulation mode during and after. The shape of the size distribution measured during the early morning peak is nearly identical to that observed during fireworks, suggesting that the early morning peak is mainly due to trapped fireworks emissions not early morning traffic. Gaseous species are less strongly influenced by fireworks than particles. Comparing measurements made between 10 pm and midnight on July 4th and the same period on July 3rd, the concentration of CO increases 32% while the COjats:sub2</jats:sub> increases only 2% but increases by another 15% overnight. The NO concentration behaves oddly, decreasing during fireworks, but then recovering the next morning, more than doubling overnight. Our measurements of CO, NO, and PMjats:sub2.5</jats:sub> are compared with those made at the nearest (~ 2 km away) Minnesota Pollution Control Agency Air Monitoring Station. Their NO results are quite different from ours with much lower concentrations before fireworks, a distinct peak during, followed by a strong overnight increase and an early morning peak somewhat similar in shape and concentration to ours. These differences are likely due mainly to malfunction of our low-cost NO sensor. Concentrations of CO and PMjats:sub2.5</jats:sub> track ours within 25% but peak shapes are somewhat different, which is not unexpected given the spatial separation of the measurements. </jats:p> </jats:sec>jats:sec jats:titleArticle highlights</jats:title> jats:p<jats:list list-type="bullet"> jats:list-item jats:pLow-cost and moderate-cost sensors are used to monitor the impact of a 4th of July fireworks display on local air quality.</jats:p> </jats:list-item> jats:list-item jats:pParticle concentrations and size are more strongly influenced by fireworks than are concentrations gaseous pollutants.</jats:p> </jats:list-item> jats:list-item jats:pParticle size distributions produced by fireworks are distinctly different from those associated with urban traffic sources.</jats:p> </jats:list-item> </jats:list></jats:p> </jats:sec>