Wildfire smoke is frequently present over the U.S. during the agricultural growing season and will likely increase with climate change. Studies of smoke impacts have largely focused on air quality and human health; however, understanding smoke’s impact on photosynthetically active radiation (PAR) is essential for predicting how smoke affects plant growth. We compare surface shortwave irradiance and diffuse fraction (DF) on smoke-impacted and smoke-free days from 2006-2020 using data from multifilter rotating shadowband radiometers at ten U.S. Department of Agriculture (USDA) UV-B Monitoring and Research Program stations and smoke plume locations from operational satellite products. On average, 20% of growing season days are smoke-impacted, but smoke prevalence increases over time (r = 0.60, p < 0.05). Smoke presence peaks in the mid- to late growing season (i.e., July, August), particularly over the northern Rocky Mountains, Great Plains, and Midwest. We find an increase in the distribution of PAR DF on smoke-impacted days, with larger increases at lower cloud fractions. On clear-sky days, daily average PAR DF increases by 10 percentage points when smoke is present. Spectral analysis of clear-sky days shows smoke increases DF (average: +45%) and decreases total irradiance (average: -6%) across all six wavelengths measured from 368-870 nm. Optical depth measurements from ground and satellite observations both indicate that spectral DF increases and total spectral irradiance decreases with increasing smoke plume optical depth. Our analysis provides a foundation for understanding smoke’s impact on PAR, which carries implications for agricultural crop productivity under a changing climate.

This dataset contains information on surface-level photosynthetically active radiation, smoke plume location, aerosol optical depth, and cloud fraction from four publicly available sources:

• U.S. Department of Agriculture's UV-B Monitoring and Research Program (UVMRP)
• National Oceanic and Atmospheric Administration/National Enviromental Satellite, Data, and Information Service's Hazard Mapping System (HMS) Smoke Product
• National Aeronautics and Space Administration's Multi-Angle Implementation of Atmospheric Correction (MAIAC) Land Aerosol Optical Depth Product (MCD19A2)
• National Aeronautics and Space Administration's Moderate Resolution Imaging Spectroradiometer (MODIS) Atmosphere L3 Daily Product (MOD08_D3, MYD08_D3)

The dataset covers 10 UVMRP stations located across the contiguous U.S.:

• Davis, California
• Pullman, Washington
• Pawnee, Nunn, Colorado
• Poplar, Montana
• Fargo, North Dakota
• Billings, Oklahoma
• Grand Rapids, Minnesota
• Bondville, Illinois
• Starkville, Mississippi
• Geneva, New York

These sites were selected to provide broad spatial coverage of the regions analyzed in the Brey et al. (2018) smoke climatology, capture much of the smoke variability across the U.S., align with agricultural areas, and reduce the impact of metropolitan air pollution. The UVMRP staff were instrumental in providing the underlying UVMRP data and advise on working with the data. Extensive cleaning was conducted to remove data anomalies, quality control issues, and high solar zenith angles (> 75 degrees). Additional processing of underlying records created additional factors, such as average diffuse fraction, used for analysis. We also averaged values to a daily resolution.

A detailed description of the site selection, data cleaning, and data processing methods used to produce this final merged dataset are available in the article by Corwin et al. entitled "Smoke-driven changes in photosynthetically active radiation during the U.S. agricultural growing season."