Quantifying global terrestrial methanol emissions using observations from the TES satellite sensor

Light oxygenated volatile organic compound concentrations in an Eastern Mediterranean urban atmosphere rivalling those in megacities

Highly resolved measurements of primary and secondary oxygenated volatile organic compounds (OVOCs) by proton-transfer-reaction mass spectrometry (PTR-MS) and the AMOVOC sampler (Airborne Measurements Of VOC) were performed in Beirut, Lebanon, during the ECOCEM (Emissions and Chemistry of Organic Carbon in the East Mediterranean) experiments. The OVOC concentrations (0.15-7.0 ppb) rival those reported for international megacities like Paris, Tokyo, or São Paulo (0.3-6.5 ppb). This study highlights the seasonal variability of OVOCs, the potential role of background pollution on OVOC concentrations, traffic emissions of OVOCs, and the secondary production of OVOCs during both summer and winter. The primary and secondary OVOC fractions were estimated using two methods based on the night-time emission ratio and photochemical age. Our calculations coupled with a correlation analysis revealed the following: firstly, background concentrations contributed significantly, especially for longer-lived OVOCs, such as methanol and acetone (30%-80%). Secondly, secondary production in summer increased up to 60%, except for methanol and isoprene oxidation products, i.e., for methacrolein and methyl vinyl ketone. Thirdly, the secondary production in the Eastern Mediterranean persisted in winter, and finally, strong primary traffic emissions dominated the primary biogenic emissions. Finally, the emission ratios were used to evaluate the global anthropogenic emission inventories downscaled to Lebanon. Although limited to two individual non-lumped species (formaldehyde and acetone), the emission ratios compared well, within a factor of 2. However, the emissions of aldehydes and ketones from the CAMS, Edgar, and MACCITY inventories showed discrepancies of up to three orders of magnitude. This demonstrates a need for improved OVOC representation in emission inventories, considering the atmospheric relevance and abundance of OVOCs and their use in volatile chemical products.

Methylotrophic bacteria from rice paddy soils: mineral-nitrogen-utilizing isolates richness in bulk soil and rhizosphere

Methanol, the second most abundant volatile organic compound, primarily released from plants, is a major culprit disturbing atmospheric chemistry. Interestingly, ubiquitously found methanol-utilizing bacteria, play a vital role in mitigating atmospheric methanol effects. Despite being extensively characterized, the effect of nitrogen sources on the richness of methanol-utilizers in the bulk soil and rhizosphere is largely unknown. Therefore, the current study was planned to isolate, characterize and explore the richness of cultivable methylotrophs from the bulk soil and rhizosphere of a paddy field using media with varying nitrogen sources. Our data revealed that more genera of methylotrophs, including Methylobacterium, Ancylobacter, Achromobacter, Xanthobacter, Moraxella, and Klebsiella were enriched with the nitrate-based medium compared to only two genera, Hyphomicrobium and Methylobacterium, enriched with the ammonium-based medium. The richness of methylotrophic bacteria also differed substantially in the bulk soil as compared to the rhizosphere. Growth characterization revealed that majority of the newly isolated methanol-utilizing strains in this study exhibited better growth at 37 °C instead of 30 or 45 °C. Moreover, Hyphomicrobium sp. FSA2 was the only strain capable of utilizing methanol even at elevated temperature 45 °C, showing its adaptability to a wide range of temperatures. Differential carbon substrate utilization profiling revealed the facultative nature of all isolated methanol-utilizer strains with Xanthobacter sp. TS3, being an important methanol-utilizer capable of degrading toxic compounds such as acetone and ethylene glycol. Overall, our study suggests the role of nutrients and plant-microbial interaction in shaping the composition of methanol-utilizers in terrestrial environment.

Assessing the regional biogenic methanol emission from spring wheat during the growing season: A Canadian case study

As a volatile organic compound existing in the atmosphere, methanol plays a key role in atmospheric chemistry due to its comparatively high abundance and long lifetime. Croplands are a significant source of biogenic methanol, but there is a lack of systematic assessment for the production and emission of methanol from crops in various phases. In this study, methanol emissions from spring wheat during the growing period were estimated using a developed emission model. The temporal and spatial variations of methanol emissions of spring wheat in a Canadian province were investigated. The averaged methanol emission of spring wheat is found to be 37.94 ± 7.5 μg·m^-2·h^-1, increasing from north to south and exhibiting phenological peak to valley characteristics. Moreover, cold crop districts are projected to be with higher increase in air temperature and consequent methanol emissions during 2020-2099. Furthermore, the seasonality of methanol emissions is found to be positively correlated to concentrations of CO, filterable particulate matter, and PM₁₀ but negatively related to NO₂ and O₃. The uncertainty and sensitivity analysis results suggest that methanol emissions show a Gamma probabilistic distribution, and growth length, air temperature, solar radiation and leafage are the most important influencing variables. In most cases, methanol emissions increase with air temperature in the range of 3-35 °C while the excessive temperature may result in decreased methanol emissions because of inactivated enzyme activity or increased instant methanol emissions due to heat injury. Notably, induced emission might be the major source of biogenic methanol of mature leaves. The results of this study can be used to develop appropriate strategies for regional emission management of cropping systems.

Bidirectional Ecosystem-Atmosphere Fluxes of Volatile Organic Compounds Across the Mass Spectrum: How Many Matter?

Terrestrial ecosystems are simultaneously the largest source and a major sink of volatile organic compounds (VOCs) to the global atmosphere, and these two-way fluxes are an important source of uncertainty in current models. Here, we apply high-resolution mass spectrometry (proton transfer reaction-quadrupole interface time-of-flight; PTR-QiTOF) to measure ecosystem-atmosphere VOC fluxes across the entire detected mass range (m/z 0-335) over a mixed temperate forest and use the results to test how well a state-of-science chemical transport model (GEOS-Chem CTM) is able to represent the observed reactive carbon exchange. We show that ambient humidity fluctuations can give rise to spurious VOC fluxes with PTR-based techniques and present a method to screen for such effects. After doing so, 377 of the 636 detected ions exhibited detectable gross fluxes during the study, implying a large number of species with active ecosystem-atmosphere exchange. We introduce the reactivity flux as a measure of how Earth-atmosphere fluxes influence ambient OH reactivity and show that the upward total VOC (∑VOC) carbon and reactivity fluxes are carried by a far smaller number of species than the downward fluxes. The model underpredicts the ∑VOC carbon and reactivity fluxes by 40-60% on average. However, the observed net fluxes are dominated (90% on a carbon basis, 95% on a reactivity basis) by known VOCs explicitly included in the CTM. As a result, the largest CTM uncertainties in simulating VOC carbon and reactivity exchange for this environment are associated with known rather than unrepresented species. This conclusion pertains to the set of species detectable by PTR-TOF techniques, which likely represents the majority in terms of carbon mass and OH reactivity, but not necessarily in terms of aerosol formation potential. In the case of oxygenated VOCs, the model severely underpredicts the gross fluxes and the net exchange. Here, unrepresented VOCs play a larger role, accounting for ~30% of the carbon flux and ~50% of the reactivity flux. The resulting CTM biases, however, are still smaller than those that arise from uncertainties for known and represented compounds.

A Large Underestimate of Formic Acid from Tropical Fires: Constraints from Space-Borne Measurements

Formic acid (HCOOH) is one of the most abundant carboxylic acids and a dominant source of atmospheric acidity. Recent work indicates a major gap in the HCOOH budget, with atmospheric concentrations much larger than expected from known sources. Here, we employ recent space-based observations from the Tropospheric Emission Spectrometer with the GEOS-Chem atmospheric model to better quantify the HCOOH source from biomass burning, and assess whether fire emissions can help close the large budget gap for this species. The space-based data reveal a severe model HCOOH underestimate most prominent over tropical burning regions, suggesting a major missing source of organic acids from fires. We develop an approach for inferring the fractional fire contribution to ambient HCOOH and find, based on measurements over Africa, that pyrogenic HCOOH:CO enhancement ratios are much higher than expected from direct emissions alone, revealing substantial secondary organic acid production in fire plumes. Current models strongly underestimate (by 10 ± 5 times) the total primary and secondary HCOOH source from African fires. If a 10-fold bias were to extend to fires in other regions, biomass burning could produce 14 Tg/a of HCOOH in the tropics or 16 Tg/a worldwide. However, even such an increase would only represent 15-20% of the total required HCOOH source, implying the existence of other larger missing sources.

Enhanced methanol sensing properties of SnO2 microspheres in a composite with Pt nanoparticles

SnO₂ microspheres in a composite with Pt nanoparticles (0, 0.5, 1.5, 2.5, 5.0 mol% Pt loading) were synthesized by a solvothermal method.

HCOOH measurements from space: TES retrieval algorithm and observed global distribution

Presented is a detailed description of the TES (Tropospheric Emission Spectrometer)-Aura satellite formic acid (HCOOH) retrieval algorithm and initial results quantifying the global distribution of tropospheric HCOOH. The retrieval strategy, including the optimal estimation methodology, spectral microwindows, a priori constraints, and initial guess information, are provided. A comprehensive error and sensitivity analysis is performed in order to characterize the retrieval performance, degrees of freedom for signal, vertical resolution, and limits of detection. These results show that the TES HCOOH retrievals (i) typically provide at best 1.0 pieces of information; (ii) have the most vertical sensitivity in the range from 900 to 600 hPa with ~2 km vertical resolution; (iii) require at least 0.5 ppbv (parts per billion by volume) of HCOOH for detection if thermal contrast is greater than 5 K, and higher concentrations as thermal contrast decreases; and (iv) based on an ensemble of simulated retrievals, are unbiased with a standard deviation of ±0.4 ppbv. The relative spatial distribution of tropospheric HCOOH derived from TES and its associated seasonality are broadly correlated with predictions from a state-of-the-science chemical transport model (GEOS-Chem CTM). However, TES HCOOH is generally higher than is predicted by GEOS-Chem, and this is in agreement with recent work pointing to a large missing source of atmospheric HCOOH. The model bias is especially pronounced in summertime and over biomass burning regions, implicating biogenic emissions and fires as key sources of the missing atmospheric HCOOH in the model.