Atmospheric biogenic volatile organic compounds in the Alaskan Arctic tundra: constraints from measurements at Toolik Field Station

Abstract

Abstract. The Arctic is a climatically sensitive region that has experienced warming at almost 3 times the global average rate in recent decades, leading to an increase in Arctic greenness and a greater abundance of plants that emit biogenic volatile organic compounds (BVOCs). These changes in atmospheric emissions are expected to significantly modify the overall oxidative chemistry of the region and lead to changes in VOC composition and abundance, with implications for atmospheric processes. Nonetheless, observations needed to constrain our current understanding of these issues in this critical environment are sparse. This work presents novel atmospheric in situ proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) measurements of VOCs at Toolik Field Station (TFS; 68∘38′ N, 149∘36' W), in the Alaskan Arctic tundra during May–June 2019. We employ a custom nested grid version of the GEOS-Chem chemical transport model (CTM), driven with MEGANv2.1 (Model of Emissions of Gases and Aerosols from Nature version 2.1) biogenic emissions for Alaska at 0.25∘ × 0.3125∘ resolution, to interpret the observations in terms of their constraints on BVOC emissions, total reactive organic carbon (ROC) composition, and calculated OH reactivity (OHr) in this environment. We find total ambient mole fraction of 78 identified VOCs to be 6.3 ± 0.4 ppbv (10.8 ± 0.5 ppbC), with overwhelming (> 80 %) contributions are from short-chain oxygenated VOCs (OVOCs) including methanol, acetone and formaldehyde. Isoprene was the most abundant terpene identified. GEOS-Chem captures the observed isoprene (and its oxidation products), acetone and acetaldehyde abundances within the combined model and observation uncertainties (±25 %), but underestimates other OVOCs including methanol, formaldehyde, formic acid and acetic acid by a factor of 3 to 12. The negative model bias for methanol is attributed to underestimated biogenic methanol emissions for the Alaskan tundra in MEGANv2.1. Observed formaldehyde mole fractions increase exponentially with air temperature, likely reflecting its biogenic precursors and pointing to a systematic model underprediction of its secondary production. The median campaign-calculated OHr from VOCs measured at TFS was 0.7 s−1, roughly 5 % of the values typically reported in lower-latitude forested ecosystems. Ten species account for over 80 % of the calculated VOC OHr, with formaldehyde, isoprene and acetaldehyde together accounting for nearly half of the total. Simulated OHr based on median-modeled VOCs included in GEOS-Chem averages 0.5 s−1 and is dominated by isoprene (30 %) and monoterpenes (17 %). The data presented here serve as a critical evaluation of our knowledge of BVOCs and ROC budgets in high-latitude environments and represent a foundation for investigating and interpreting future warming-driven changes in VOC emissions in the Alaskan Arctic tundra.

Assessing formic and acetic acid emissions and chemistry in western U.S. wildfire smoke: implications for atmospheric modeling

“…8 are not due to near-field production in BB, though enhancement in much more aged plumes (>2 days) has been observed. 102,103 As methanol and acetone are known to be major primary emissions and secondary products from biogenic sources, 12,31,102,104–106 we hypothesize that their strong correlation with FA during WE-CAN and FIREX-AQ indicates that a portion of the observed FA may be of biogenic origin, though the long atmospheric lifetimes of all three species (>2 days) likely also play a role in why they are well correlated with each other.…”

“…This low model bias is most pronounced in biogenic source regions, 7,8 including United States (U.S.) deciduous forests, 9,10 boreal forests, 11 tropical forests, 6 and in the Arctic tundra. 12 Additionally, models typically fail to capture FA and AA enhancements in plumes from mixed anthropogenic sources 13,14 and in biomass burning (BB) impacted regions, [15][16][17] indicating potential missing primary and/or secondary sources in smoke. In this work, we investigate emissions, secondary productions, and model representations of FA and AA in the western U.S. during two wildre seasons, using measurements made during the WE-CAN (Western Wildre Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen) and FIREX-AQ (Fire Inuence on Regional to Global Environments and Air Quality) eld campaigns.…”

Arctic Heatwaves Could Significantly Influence the Isoprene Emissions From Shrubs

“…is a prevalent source of isoprene in high latitude ecosystems (Li et al, 2023;Potosnak et al, 2013;Simin et al, 2021). Recent whole-ecosystem measurements suggest that the temperature response of isoprene emissions in high-latitude tundra ecosystems is stronger than what current isoprene emission models predict (Angot et al, 2020;Holst et al, 2010;Li et al, 2023;Seco et al, 2020Seco et al, , 2022Selimovic et al, 2022;Vettikkat et al, 2023). In contrast, leaf/branch-level studies showed that the hourly temperature response of Arctic willow species (Salix pulchra Cham.…”

Interannual variability of summertime formaldehyde (HCHO) vertical column density and its main drivers at northern high latitudes

“…The model-satellite discrepancies outside wildfire areas could be also due to model underestimates of oxygenated VOCs (OVOCs), biogenic VOC emissions and biases in satellite HCHO retrieval products. For example, Selimovic et al (2022) found that GEOS-Chem underestimates OVOCs, including HCHO, by a factor of 3-12 at Toolik Field Station in northern Alaska. Stavrakou et al (2015) show model underestimations of biogenic isoprene emissions and wildfire emissions over eastern Europe and Alaska.…”

“…This BVOC speciation appears to be different in the boreal forests in Alaska, northern Canada and eastern Siberia, where isoprene appears to be the most abundant BVOC species (Blake et al, 1992;Timkovsky et al, 2010;Zhao et al, 2022). BVOC measurements in tundra systems show a very strong positive temperature dependence for isoprene fluxes over Greenland (Vedel-Petersen et al, 2015;Kramshøj et al, 2016;Lindwall et al, 2016a), northern Sweden (Faubert et al, 2010;Tang et al, 2016) and the Alaska North Slope (Potosnak et al, 2013;Angot et al, 2020;Selimovic et al, 2022).…”