Electroediting of Soft Polymer Backbones Fried, Alan D.; Wilson, Breana J.; Galan, Nicholas J. ...
Journal of the American Chemical Society,
05/2022, Letnik:
144, Številka:
20
Journal Article
Recenzirano
Synthetic methods that edit soft polymer backbones are critical technologies for tailoring the structures and properties of macromolecules. Developing strategies that leverage underexplored reaction ...manifolds are vital for accessing new chemical (and functional) space in soft materials. Here, we report a mild electrochemical approach that enables both degradation and functionalization of synthetic polymers. We found that bulk electrolysis (under either homogeneous or heterogeneous conditions) promoted facile, chemoselective chain scission in a variety of olefin-containing materials. Polymer degradation could also be coupled with functionalization (e.g., azidation) to afford new species that could serve as macromonomers.
Biomass-derived polymers are emerging as critically needed alternatives to their petrochemical counterparts. Terpenes, which are among the most abundant natural products, represent particularly ...fertile chemical space for monomer development (given their inherent structural complexity). Here, we present the living vinyl-addition polymerization of β-pinadiene (the cumulated congener of β-pinene) at room temperature. Employing (π-allyl)NiOCOCF32 as a catalyst afforded the desired polymers with good control over molecular weight and dispersity. Interestingly, the bicyclic pinane core was retained in the isolated materials (which starkly contrasts prototypical pinene polymerizations). Moreover, the reported materials exhibited impressive thermal stability (T d = 294 °C) and high glass transition temperatures (T g = 160 °C). As the polymerization of terpene-derived cumulenes can afford scaffolds that defy current synthetic logic, we anticipate our work will unlock additional avenues for sustainable polymer development.
The nonlinear chemical processes involved in ozone production (P(O3)) have necessitated using proxy indicators to convey information about the primary dependence of P(O3) on volatile organic ...compounds (VOCs) or nitrogen oxides (NOx). In particular, the ratio of remotely sensed columns of formaldehyde (HCHO) to nitrogen dioxide (NO2) has been widely used for studying O3 sensitivity. Previous studies found that the errors in retrievals and the incoherent relationship between the column and the near-surface concentrations are a barrier in applying the ratio in a robust way. In addition to these obstacles, we provide calculational-observational evidence, using an ensemble of 0-D photochemical box models constrained by DC-8 aircraft measurements on an ozone event during the Korea-United States Air Quality (KORUS-AQ) campaign over Seoul, to demonstrate the chemical feedback of NO2 on the formation of HCHO is a controlling factor for the transition line between NOx-sensitive and NOx-saturated regimes. A fixed value (~2.7) of the ratio of the chemical loss of NOx (LNOx) to the chemical loss of HO2+RO2 (LROx) perceptibly differentiates the regimes. Following this value, data points with a ratio of HCHO/NO2 less than 1 can be safely classified as NOx-saturated regime, whereas points with ratios between 1 and 4 fall into one or the other regime. We attribute this mainly to the HCHO-NO2 chemical relationship causing the transition line to occur at larger (smaller) HCHO/NO2 ratios in VOC-rich (VOC-poor) environments. We then redefine the transition line to LNOx/LROx~2.7 that accounts for the HCHO-NO2 chemical relationship leading to HCHO = 3.7 × (NO2 – 1.14 × 1016 molec.cm-2). Although the revised formula is locally calibrated (i.e., requires for readjustment for other regions), its mathematical format removes the need for having a wide range of thresholds used in HCHO/NO2 ratios that is a result of the chemical feedback. Therefore, to be able to properly take the chemical feedback into consideration, the use of HCHO = a × (NO2 – b) formula should be preferred to the ratio in future works. We then use the Geostationary Trace gas and Aerosol Sensor Optimization (GeoTASO) airborne instrument to study O3 sensitivity in Seoul. The unprecedented spatial (250 × 250 m2) and temporal (~every 2 h) resolutions of HCHO and NO2 observations form the sensor enhance our understanding of P(O3) in Seoul; rather than providing a crude label for the entire city, more in-depth variabilities in chemical regimes are observed that should be able to inform mitigation strategies correspondingly.
•Ozone sensitivity over Seoul on an exceptionally degraded air quality day.•Various thresholds for HCHO/NO2 should be defined to label chemical regimes.•The inherent dependence of HCHO production on NOx levels complicates the ratio.•We redesign the formula to reflect the chemical feedback of NOx on HCHO.•GeoTASO provides in-depth variabilities in chemical regimes over Seoul.
Organic aerosol (OA) is an important fraction of submicron aerosols. However,
it is challenging to predict and attribute the specific organic compounds and
sources that lead to observed OA loadings, ...largely due to contributions from
secondary production. This is especially true for megacities surrounded by
numerous regional sources that create an OA background. Here, we utilize
in situ gas and aerosol observations collected on board the NASA DC-8 during
the NASA–NIER KORUS-AQ (Korea–United States Air Quality) campaign to
investigate the sources and hydrocarbon precursors that led to the secondary
OA (SOA) production observed over Seoul. First, we investigate the
contribution of transported OA to total loadings observed over Seoul by
using observations over the Yellow Sea coupled to FLEXPART Lagrangian
simulations. During KORUS-AQ, the average OA loading advected into Seoul was
∼1–3 µg sm−3. Second, taking this background into
account, the dilution-corrected SOA concentration observed over Seoul was
∼140 µgsm-3ppmv-1 at 0.5 equivalent photochemical
days. This value is at the high end of what has been observed in other
megacities around the world (20–70 µgsm-3ppmv-1 at 0.5
equivalent days). For the average OA concentration observed over Seoul
(13 µg sm−3), it is clear that production of SOA from locally
emitted precursors is the major source in the region. The importance
of local SOA production was supported by the following observations.
(1) FLEXPART source contribution calculations indicate any
hydrocarbons with a lifetime of less than 1 day, which are shown to dominate the
observed SOA production, mainly originate from South Korea. (2) SOA
correlated strongly with other secondary photochemical species, including
short-lived species (formaldehyde, peroxy acetyl nitrate, sum of acyl peroxy
nitrates, dihydroxytoluene, and nitrate aerosol). (3) Results from
an airborne oxidation flow reactor (OFR), flown for the first time, show a
factor of 4.5 increase in potential SOA concentrations over Seoul versus over
the Yellow Sea, a region where background air masses that are advected into
Seoul can be measured. (4) Box model simulations reproduce SOA
observed over Seoul within 11 % on average and suggest that short-lived
hydrocarbons (i.e., xylenes, trimethylbenzenes, and semi-volatile and intermediate-volatility compounds) were the main SOA precursors over Seoul. Toluene
alone contributes 9 % of the modeled SOA over Seoul. Finally, along with
these results, we use the metric ΔOA/ΔCO2 to
examine the amount of OA produced per fuel consumed in a megacity, which
shows less variability across the world than ΔOA∕ΔCO.
Isoprene emissions from vegetation have a large effect on
atmospheric chemistry and air quality. “Bottom-up” isoprene emission
inventories used in atmospheric models are based on limited vegetation
...information and uncertain land cover data, leading to potentially large
errors. Satellite observations of atmospheric formaldehyde (HCHO), a
high-yield isoprene oxidation product, provide “top-down” information to
evaluate isoprene emission inventories through inverse analyses. Past inverse
analyses have however been hampered by uncertainty in the HCHO satellite
data, uncertainty in the time- and NOx-dependent yield of HCHO from
isoprene oxidation, and coarse resolution of the atmospheric models used for
the inversion. Here we demonstrate the ability to use HCHO satellite data
from OMI in a high-resolution inversion to constrain isoprene emissions on
ecosystem-relevant scales. The inversion uses the adjoint of the GEOS-Chem
chemical transport model at 0.25∘ × 0.3125∘
horizontal resolution to interpret observations over the southeast US in
August–September 2013. It takes advantage of concurrent NASA SEAC4RS
aircraft observations of isoprene and its oxidation products including HCHO
to validate the OMI HCHO data over the region, test the GEOS-Chem isoprene
oxidation mechanism and NOx environment, and independently evaluate the
inversion. This evaluation shows in particular that local model errors in
NOx concentrations propagate to biases in inferring isoprene emissions
from HCHO data. It is thus essential to correct model NOx biases, which
was done here using SEAC4RS observations but can be done more generally
using satellite NO2 data concurrently with HCHO. We find in our
inversion that isoprene emissions from the widely used MEGAN v2.1 inventory
are biased high over the southeast US by 40 % on average, although the
broad-scale distributions are correct including maximum emissions in
Arkansas/Louisiana and high base emission factors in the oak-covered Ozarks
of southeast Missouri. A particularly large discrepancy is in the Edwards
Plateau of central Texas where MEGAN v2.1 is too high by a factor of 3,
possibly reflecting errors in land cover. The lower isoprene emissions
inferred from our inversion, when implemented into GEOS-Chem, decrease
surface ozone over the southeast US by 1–3 ppb and decrease the isoprene
contribution to organic aerosol from 40 to 20 %.
We report on the development and airborne field deployment of a mid-IR laser-based spectrometer. The instrument was configured for the simultaneous in situ detection of formaldehyde (CH
2
O) and ...ethane (C
2
H
6
). Numerous mechanical, optical, electronic, and software improvements over a previous instrument design resulted in reliable highly sensitive airborne operation with long stability times yielding 90 % airborne measurement coverage during the recent air quality study over the Colorado Front Range, FRAPPÉ 2014. Airborne detection sensitivities of ~15 pptv (C
2
H
6
) and ~40 pptv (CH
2
O) were generally obtained for 1 s of averaging for simultaneous detection.
The Korea-United States Air Quality Study (KORUS-AQ) conducted during May-June 2016 offered the first opportunity to evaluate direct-sun observations of formaldehyde (HCHO) total column densities ...with improved Pandora spectrometer instruments. The measurements highlighted in this work were conducted both in the Seoul megacity area at the Olympic Park site (37.5232° N, 27.1260° E; 26 ma.s.l.) and at a nearby rural site downwind of the city at the Mount Taehwa research forest site (37.3123° N, 127.3106° E; 160ma.s.l.). Evaluation of these measurements was made possible by concurrent ground-based in situ observations of HCHO at both sites as well as overflight by the NASA DC-8 research aircraft. The flights provided in situ measurements of HCHO to characterize its vertical distribution in the lower troposphere (0-5km). Diurnal variation in HCHO total column densities followed the same pattern at both sites, with the minimum daily values typically observed between 6:00 and 7:00 local time, gradually increasing to a maximum between 13:00 and 17:00 before decreasing into the evening. Pandora vertical column densities were compared with those derived from the DC-8 HCHO in situ measured profiles augmented with in situ surface concentrations below the lowest altitude of the DC-8 in proximity to the ground sites. A comparison between 49 column densities measured by Pandora vs. aircraft-integrated in situ data showed that Pandora values were larger by 16% with a constant offset of 0.22DU (Dobson units;
= 0.68). Pandora HCHO columns were also compared with columns calculated from the surface in situ measurements over Olympic Park by assuming a well-mixed lower atmosphere up to a ceilometer-measured mixed-layer height (MLH) and various assumptions about the small residual HCHO amounts in the free troposphere up to the tropopause. The best comparison (slope = 1.03±0.03; intercept = 0.29±0.02DU; and
= 0.78±0.02) was achieved assuming equal mixing within ceilometer-measured MLH combined with an exponential profile shape. These results suggest that diurnal changes in HCHO surface concentrations can be reasonably estimated from the Pandora total column and information on the mixed-layer height. More work is needed to understand the bias in the intercept and the slope relative to columns derived from the in situ aircraft and surface measurements.
The Korea-United States Air Quality (KORUS-AQ) field study was conducted during May-June 2016. The effort was jointly sponsored by the National Institute of Environmental Research of South Korea and ...the National Aeronautics and Space Administration of the United States. KORUS-AQ offered an unprecedented, multi-perspective view of air quality conditions in South Korea by employing observations from three aircraft, an extensive ground-based network, and three ships along with an array of air quality forecast models. Information gathered during the study is contributing to an improved understanding of the factors controlling air quality in South Korea. The study also provided a valuable test bed for future air quality-observing strategies involving geostationary satellite instruments being launched by both countries to examine air quality throughout the day over Asia and North America. This article presents details on the KORUS-AQ observational assets, study execution, data products, and air quality conditions observed during the study. High-level findings from companion papers in this special issue are also summarized and discussed in relation to the factors controlling fine particle and ozone pollution, current emissions and source apportionment, and expectations for the role of satellite observations in the future. Resulting policy recommendations and advice regarding plans going forward are summarized. These results provide an important update to early feedback previously provided in a Rapid Science Synthesis Report produced for South Korean policy makers in 2017 and form the basis for the Final Science Synthesis Report delivered in 2020.
Formaldehyde (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.
The Deep Convective Clouds and Chemistry (DC3) field experiment produced an exceptional dataset on thunderstorms, including their dynamical, physical, and electrical structures and their impact on ...the chemical composition of the troposphere. The field experiment gathered detailed information on the chemical composition of the inflow and outflow regions of midlatitude thunderstorms in northeast Colorado, west Texas to central Oklahoma, and northern Alabama. A unique aspect of the DC3 strategy was to locate and sample the convective outflow a day after active convection in order to measure the chemical transformations within the upper-tropospheric convective plume. These data are being analyzed to investigate transport and dynamics of the storms, scavenging of soluble trace gases and aerosols, production of nitrogen oxides by lightning, relationships between lightning flash rates and storm parameters, chemistry in the upper troposphere that is affected by the convection, and related source characterization of the three sampling regions. DC3 also documented biomass-burning plumes and the interactions of these plumes with deep convection.
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