The Effects of Smoke from Wildfires in the Western US on Urban Air Quality in Northern Nevada

In 2020, several wildfires in the western United States (US) affected regional air quality in northern Nevada for weeks. To assess the contribution of wildfire smoke to air quality in the Reno-Sparks (Nevada) area, air pollutants were measured and analyzed during a smoke-free period (August to October 2019) and compared to a smoke-affected period (August to October 2020). The ambient concentrations of fine particulate matter (PM_2.5), organic carbon (OC), and elemental carbon (EC) measured at a US Environmental Protection Agency (EPA) monitoring station in the Reno-Sparks area during smoke-affected days were on average 35.17±25.60 μg m^-3, 16.76±11.95 μg m^-3, and 4.91±4.03 μg m^-3, respectively. These concentrations are approximately 8 to 9.6 times higher than the concentrations collected on smoke-free days. In contrast, ozone (O₃) concentrations increased by only approximately 12% during smoke-affected days. On 18 of the 50 smoke-affected days, PM_2.5 concentrations exceeded the primary 24-hour EPA National Ambient Air Quality Standard of 35 μg m^-3. Particle-phase, PM_2.5-bound polycyclic aromatic hydrocarbons (PAHs) were collected on filters over a 24-hour period, extracted, and quantitatively analyzed for 104 PAHs using gas chromatography-mass spectrometry (GC-MS). Total PM_2.5-bound PAHs were approximately 6.3 times higher during smoke-affected days (mean: 4.87±3.49 ng m^-3) than during smoke-free days (mean: 0.77±0.65 ng m^-3), with dimethylnaphthalenes (1.4-, 1.5-, and 2,3-dimethylnaphthalene) dominating the smoke-affected PM_2.5 samples. Analysis of gas-phase PAHs in smoke-affected samples collected using XAD-resin cartridges revealed that the total concentration was approximately 47 times more than in PM_2.5 samples, with naphthalene being the most abundant gas-phase PAH.