Anthropogenic, biogenic, and photochemical influences on surface formaldehyde and its significant decadal (2006–2017) decrease in the Lewiston-Clarkston valley of the northwestern United States

• Published in: Chemosphere (Oxford) 2024-02, Vol.349, p.140962-140962, Article 140962
• Main Authors: Li, R., Jobson, B.T., Wen, M., Li, A.L., Huangfu, Y., Zhang, W., Hardy, R., O'Keeffe, P., Simpson, J., Fauci, M., Paden, N.
• Format: Article
• Language: English
• Subjects: Air Pollutants - analysis; Biogenic VOCs; Environment; Environmental Monitoring - methods; Field measurements; Formaldehyde (HCHO) sources; Formaldehyde - analysis; Long-term surface HCHO trend; Northwestern United States; Ozone - analysis; Secondary formation; Source apportionment; Volatile Organic Compounds - analysis
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2023.140962

Formaldehyde (HCHO) is a key carcinogen and plays an important role in atmospheric chemistry. Both field measurements and Positive Matrix Factorization (PMF) modeling have been employed to investigate the concentrations and sources of HCHO in the Lewiston-Clarkston (LC) valley of the mountainous northwestern U.S. Different instruments were deployed to measure surface formaldehyde and other related compounds in July of 2016 and 2017. The measurements reveal that the average HCHO concentrations have significantly decreased to 2–5 ppb in the LC valley in comparison to its levels (10–20 ppb) observed in July 2006. This discovery with surface measurements deserves attention given that satellite retrievals showed an increasing long-term trend from 2005 to 2014 in total vertical column density of HCHO in the region, suggesting that satellite instruments may not adequately resolve small valleys in the mountainous region. Our PMF modeling identified four major sources of HCHO in the valley: (1) emissions from a local paper mill, (2) secondary formation and background, (3) biogenic sources, and (4) traffic. This study reveals that the emissions from the paper mill cause high HCHO spikes (6–19 ppb) in the early morning. It is found that biogenic volatile organic compounds (VOCs) in the area are influenced by national forests surrounding the region (e.g., Nez Perce-Clearwater, Umatilla, Wallowa-Whitman, and Idaho Panhandle National Forests). The results provide useful information for developing strategies to control HCHO levels and have implications for future HCHO studies in atmospheric chemistry, which affects secondary aerosols and ozone formation. [Display omitted] •Significant decadal decrease in surface HCHO was discovered in a valley in Northwest.•Surface HCHO trend in the small valley is opposite to that of satellite column data.•HCHO sources include paper mill, photochemical, biogenic and traffic influences.•Volatile organic compounds (VOCs) in the area are influenced by national forests.•The methods can be used to study sources of HCHO and other toxics in any regions.