Browsing by Author "DiGangi, Joshua P."
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Item Missing OH reactivity in the global marine boundary layer(Copernicus Publications, 2020-04-02) Thames, Alexander B.; Brune, William H.; Miller, David O.; Allen, Hannah M.; Apel, Eric C.; Blake, Donald R.; Bui, T. Paul; Commane, Roisin; Crounse, John D.; Daube, Bruce C.; Diskin, Glenn S.; DiGangi, Joshua P.; Elkins, James W.; Hall, Samuel R.; Hanisco, Thomas F.; Hannun, Reem; Hintsa, Eric; Hornbrook, Rebecca S.; Kim, Michelle J.; McKain, Kathryn; Moore, Fred L.; Nicely, Julie M.; Peischl, Jeffrey; Ryerson, Thomas B.; St. Clair, Jason; Sweeney, Colm; Teng, Alex; Thompson, Chelsea R.; Ullmann, Kirk; Wennberg, Paul O.; Wolfe, GlennThe hydroxyl radical (OH) reacts with thousands of chemical species in the atmosphere, initiating their removal and the chemical reaction sequences that produce ozone, secondary aerosols, and gas-phase acids. OH reactivity, which is the inverse of OH lifetime, influences the OH abundance and the ability of OH to cleanse the atmosphere. The NASA Atmospheric Tomography (ATom) campaign used instruments on the NASA DC-8 aircraft to measure OH reactivity and more than 100 trace chemical species. ATom presented a unique opportunity to test the completeness of the OH reactivity calculated from the chemical species measurements by comparing it to the measured OH reactivity over two oceans across four seasons. Although the calculated OH reactivity was below the limit of detection for the ATom instrument used to measure OH reactivity throughout much of the free troposphere, the instrument was able to measure the OH reactivity in and just above the marine boundary layer. The mean measured value of OH reactivity in the marine boundary layer across all latitudes and all ATom deployments was 1.9 s⁻¹, which is 0.5 s⁻¹ larger than the mean calculated OH reactivity. The missing OH reactivity, the difference between the measured and calculated OH reactivity, varied between 0 and 3.5 s⁻¹, with the highest values over the Northern Hemisphere Pacific Ocean. Correlations of missing OH reactivity with formaldehyde, dimethyl sulfide, butanal, and sea surface temperature suggest the presence of unmeasured or unknown volatile organic compounds or oxygenated volatile organic compounds associated with ocean emissions.Item Validation of satellite formaldehyde (HCHO) retrievals using observations from 12 aircraft campaigns(Copernicus Publications, 2020-10-29) Zhu, Lei; Abad, Gonzalo González; Nowlan, Caroline R.; Miller, Christopher Chan; Chance, Kelly; Apel, Eric C.; DiGangi, Joshua P.; Fried, Alan; Hanisco, Thomas F.; Hornbrook, Rebecca S.; Hu, Lu; Kaiser, Jennifer; Keutsch, Frank N.; Permar, Wade; St. Clair, Jason; Wolfe, GlennFormaldehyde (HCHO) has been measured from space for more than 2 decades. Owing to its short atmospheric lifetime, satellite HCHO data are used widely as a proxy of volatile organic compounds (VOCs; please refer to Appendix A for abbreviations and acronyms), providing constraints on underlying emissions and chemistry. However, satellite HCHO products from different satellite sensors using different algorithms have received little validation so far. The accuracy and consistency of HCHO retrievals remain largely unclear. Here we develop a validation platform for satellite HCHO retrievals using in situ observations from 12 aircraft campaigns with a chemical transport model (GEOS-Chem) as the intercomparison method. Application to the NASA operational OMI HCHO product indicates negative biases (−44.5 % to −21.7 %) under high-HCHO conditions, while it indicates high biases (+66.1 % to +112.1 %) under low-HCHO conditions. Under both conditions, HCHO a priori vertical profiles are likely not the main driver of the biases. By providing quick assessment of systematic biases in satellite products over large domains, the platform facilitates, in an iterative process, optimization of retrieval settings and the minimization of retrieval biases. It is also complementary to localized validation efforts based on ground observations and aircraft spirals.Item Wintertime Formaldehyde: Airborne Observations and Source Apportionment Over the Eastern United States(American Geophysical Union, 2021-01-12) Green, Jaime R.; Fiddler, Marc N.; Fibiger, Dorothy L.; McDuffie, Erin E.; Aquino, Janine; Campos, Teresa; Shah, Viral; Jaeglé, Lyatt; Thornton, Joel A.; DiGangi, Joshua P.; Wolfe, Glenn; Bililign, Solomon; Brown, Steven S.Formaldehyde (HCHO) is generated from direct urban emission sources and secondary production from the photochemical reactions of urban smog. HCHO is linked to tropospheric ozone formation, and contributes to the photochemical reactions of other components of urban smog. In this study, pollution plume intercepts during the Wintertime INvestigation of Transport, Emissions, and Reactivity (WINTER) campaign were used to investigate and characterize the formation of HCHO in relation to several anthropogenic tracers. Analysis of aircraft intercepts combined with detailed chemical box modeling downwind of several cities suggests that the most important contribution to observed HCHO was primary emission. A box model analysis of a single plume suggested that secondary sources contribute to 21 ± 10% of the observed HCHO. Ratios of HCHO/CO observed in the northeast US, from Ohio to New York, ranging from 0.2% to 0.6%, are consistent with direct emissions combined with at most modest photochemical production. Analysis of the nocturnal boundary layer and residual layer from repeated vertical profiling over urban influenced areas indicate a direct HCHO emission flux of 1.3 × 10¹⁴ molecules cm⁻² h⁻¹. In a case study in Atlanta, GA, nighttime HCHO exhibited a ratio to CO (0.6%–1.8%) and was anti-correlated with O₃. Observations were consistent with mixing between direct HCHO emissions in urban air masses with those influenced by more rapid HCHO photochemical production. The HCHO/CO emissions ratios determined from the measured data are 2.3–15 times greater than the NEI 2017 emissions database. The largest observed HCHO/CO was 1.7%–1.8%, located near co-generating power stations.