Impact of 4th of July Fireworks on Spatiotemporal PM2.5 Concentrations in California Based on the PurpleAir Sensor Network: Implications for Policy and Environmental Justice

Abstract

Fireworks are often used in celebration, causing short term, extremely high particulate matter air pollution. In recent years, the rapid development and expansion of low-cost air quality sensors by companies such as PurpleAir has enabled an understanding of air pollution at a much higher spatiotemporal resolution compared to traditional monitoring networks. In this study, real-time PM_2.5 measurements from 751 PurpleAir sensors operating from June to July in 2019 and 2020 were used to examine the impact of 4th of July fireworks on hourly and daily PM_2.5 concentrations at the census tract and county levels in California. American Community Survey (ACS) and CalEnviroScreen 3.0 data were used to identify correlations between PM_2.5 measurements and socioeconomic status (SES). A two-step method was implemented to assure the quality of raw PM_2.5 sensor data and sensor calibration against co-located reference instruments. The results showed that over 67% and 81% of counties experienced immediate impacts related to fireworks in 2019 and 2020, respectively. Relative to 2019, the peak PM_2.5 concentrations on July 4th and 5th 2020 were, on average, over 50% higher in California, likely due to the COVID-19-related increase in the use of household-level fireworks. This increase was most pronounced in southern counties, which tend to have less strict firework-related regulations and a greater use of illegal fireworks. Los Angeles County experienced the highest July 4th daily PM_2.5 levels both in 2019 (29.9 µg·m^-3) and 2020 (42.6 µg·m^-3). Spatial hot spot analyses generally showed these southern counties (e.g., Los Angeles County) to be regional air pollution hotspots, whereas the opposite pattern was seen in the north (e.g., San Francisco). The results also showed PM_2.5 peaks that were over two-times higher among communities with lower SES, higher minority group populations, and higher asthma rates. Our findings highlight the important role that policy and enforcement can play in reducing firework-related air pollution and protecting public health, as exemplified by southern California, where policy was more relaxed and air pollution was higher (especially in 2020 when the 4th of July coincided with the COVID-19-lockdown period), and in disadvantaged communities where disparities were greatest.

Keywords: Independence Day; PurpleAir; air quality; firework; low-cost sensors; particulate matter.

Figure 1

Examples of hourly average PM_2.5 concentrations from 7:00 p.m. on July 4th to 7:00 p.m. on July 5th 2020 according to three different scenarios observed in (a) Los Angeles County (high impact), (b) Orange County (moderate impact), and (c) Riverside County (low impact).

Figure 2

Spatial distribution of PurpleAir measured daily average PM_2.5 concentrations across (a) the entire state, (b) Los Angeles County, and (c) San Francisco, Bay area scheme during the 4th and 5th July period in 2019 and 2020. Panel (d) shows the spatial hotspot analysis across the state for average PM_2.5 concentration during the 4th and 5th July period in 2019 and 2020.

Figure 2

Spatial distribution of PurpleAir measured daily average PM_2.5 concentrations across (a) the entire state, (b) Los Angeles County, and (c) San Francisco, Bay area scheme during the 4th and 5th July period in 2019 and 2020. Panel (d) shows the spatial hotspot analysis across the state for average PM_2.5 concentration during the 4th and 5th July period in 2019 and 2020.

Figure 2

Spatial distribution of PurpleAir measured daily average PM_2.5 concentrations across (a) the entire state, (b) Los Angeles County, and (c) San Francisco, Bay area scheme during the 4th and 5th July period in 2019 and 2020. Panel (d) shows the spatial hotspot analysis across the state for average PM_2.5 concentration during the 4th and 5th July period in 2019 and 2020.

Figure 3

Comparison of the normalized daily PM_2.5 concentrations (average over July 4th and 5th) in cities where firework displays were either allowed or not allowed in southern and northern California, where “n” shows the number of census tracts within each category and the p-value shows the t-test results between census tracts where fireworks were either allowed or not allowed in each year.