Chemical Loss Research Articles

Review of source analyses of ambient volatile organic compounds considering reactive losses: methods of reducing loss effects, impacts of losses, and sources

Abstract. Chemical losses of ambient reactive volatile organic compounds (VOCs) is a long-term issue yet to be resolved in VOC source apportionments. These losses substantially reduce the concentrations of highly reactive species in the apportioned factor profiles and result in the underestimation of source contributions. This review assesses the common methods and existing issues in ways to reduce losses and loss impacts in source analyses and suggests research directions for improved VOC source apportionments. Positive matrix factorization (PMF) is now the main VOC source analysis method compared to other mathematical models. The issue in using any apportionment tool is the processing of the data to be analyzed to reduce the impacts of reactive losses. Estimating the initial concentrations of ambient VOCs based on photochemical age has become the primary approach to reduce reactive loss effects in PMF, except for selecting low-reactivity species or nighttime data into the analysis. Currently, the initial concentration method only considers daytime reactions with hydroxyl (⚫OH) radicals. However, the ⚫OH rate constants vary with temperature, and that has not been considered. Losses from reactions with O3 and NO3 radicals, especially for alkene species, remain to be included. Thus, the accuracy of the photochemical age estimation is uncertain. Beyond developing accurate quantitative approaches for reactive losses, source analyses methods for the consumed VOCs and the accurate quantification of different source contributions to O3 and secondary organic aerosols are important additional directions for future research.

Direct Recycling of LixNi0.5Mn0.3Co0.2O2 from Production Scrap and End‐Of‐Life Batteries, Using Solid‐State Relithiation

AbstractDirect recycling of Li‐ion battery cathodes offers a sustainable and potentially cost‐effective alternative to conventional methods, often involving complex chemical processes and significant material losses. This study focuses on the relithiation of cathode materials from quality control reject (QCR) and end‐of‐life (EoL) Li‐ion cells to restore their physical structure, morphology, and electrochemical performance. Two NMC532/graphite pouch cells from the same manufacturer were studied. QCR cells, stored under ambient conditions, experienced corrosion and degradation before recycling, while EoL cells were cycled to the end of life. The cells were disassembled, and the cathode materials were delaminated using NaOH solution, then relithiated with LiOH at 700 °C for 15 hours in the air. Extensive characterization analyzed elemental composition, structural properties, thermal stability, and particle size distribution. Results indicated that relithiation successfully restored lithium content and improved the structural ordering and morphology of the cathode materials. The electrochemical performance of the relithiated cathodes exhibited good stability over 100 charge‐discharge cycles. The relithiated QCR samples achieved a capacity of 155.57 mAh g−1, while EoL samples reached 152.53 mAh g−1, comparable to pristine materials. This study highlights relithiation's potential to extend the lifecycle of Li‐ion cathodes, contributing to a more sustainable circular economy for battery materials.

Validation of GEMS tropospheric NO2 columns and their diurnal variation with ground-based DOAS measurements

Abstract. Instruments for air quality observations on geostationary satellites provide multiple observations per day and allow for the analysis of the diurnal variation in important air pollutants such as nitrogen dioxide (NO2). The South Korean instrument GEMS (Geostationary Environmental Monitoring Spectrometer), launched in February 2020, is the first geostationary instrument that is able to observe the diurnal variation in NO2. The measurements have a spatial resolution of 3.5 km × 8 km and cover a large part of Asia. This study compares 1 year of tropospheric NO2 vertical column density (VCD) observations from the operational GEMS L2 product, the scientific GEMS IUP-UB (Institute of Environmental Physics at the University of Bremen) product, the operational TROPOspheric Monitoring Instrument (TROPOMI) product, and ground-based differential optical absorption spectroscopy (DOAS) measurements in South Korea. The GEMS L2 tropospheric NO2 VCDs overestimate the ground-based tropospheric NO2 VCDs with a median relative difference of +61 % and a correlation coefficient of 0.76. The median relative difference is −2 % for the GEMS IUP-UB product and −16 % for the TROPOMI product, with correlation coefficients of 0.83 and 0.89, respectively. The scatter in the GEMS products can be reduced when observations are limited to the TROPOMI overpass time. Diurnal variations in tropospheric NO2 VCDs differ by the pollution level of the analyzed site but with good agreement between the GEMS IUP-UB and ground-based observations. Low-pollution sites show weak or almost no diurnal variation. In summer, the polluted sites show a minimum around noon, indicating the large influence of photochemical loss. Most variation is seen in spring and autumn, with increasing NO2 in the morning, a maximum close to noon, and a decrease towards the afternoon. Winter observations show rather flat or slightly decreasing NO2 throughout the day. Winter observations under low-wind-speed conditions at high-pollution sites show enhancements of NO2 throughout the day. This indicates that under calm conditions, dilution and the less effective chemical loss in winter do not balance the accumulating emissions. Diurnal variation observed at a low-pollution site follows seasonal wind patterns. A weekday–weekend effect analysis shows good agreement between the different products. However, the GEMS L2 product, while agreeing with the other data sets on weekdays, shows significantly less reduction on weekends. The influence of the stratospheric contribution and the surface reflectivity product on the satellite tropospheric NO2 VCD products is investigated. While the TM5 model's stratospheric VCDs, used in the TROPOMI product, are too high, resulting in tropospheric NO2 VCDs that are too low and even negative, when used in the GEMS IUP-UB retrieval, the GEMS L2 stratospheric VCD is too low. Surface reflectivity comparisons indicate that the GEMS L2 reflectivity makes a large contribution to the observed overestimation and scatter.

Synaptic composition, activity, mRNA translation and dynamics in combined single-synapse profiling using multimodal imaging.

The function of neuronal circuits, and its perturbation by psychoactive molecules or disease-associated genetic variants, is governed by the interplay between synapse activity and synaptic protein localization and synthesis across a heterogeneous synapse population. Here, we combine in situ measurement of synaptic multiprotein compositions and activation states, synapse activity in calcium traces or glutamate spiking, and local translation of specific genes, across the same individual synapses. We demonstrate how this high-dimensional data enables identification of interdependencies in the multiprotein-activity network, and causal dissection of complex synaptic phenotypes in disease-relevant chemical and genetic NMDAR loss of function that translate in vivo . We show how this method generalizes to other subcellular systems by deriving mitochondrial protein networks, and, using support vector machines, its value in overcoming animal variability in phenotyping. Integrating multiple synapse information modalities enables deep structure-function characterization of synapse populations and their responses to genetic and chemical perturbations.

Rapid Uplift, yet Slow Denudation of the Suckling‐Dayman Metamorphic Core Complex in Tropical Papua New Guinea

AbstractA linear relationship between rates of physical erosion and chemical weathering is apparent in slowly eroding landscapes. Whether the relationship remains linear in rapidly eroding landscapes is less clear. Field‐based research into this relationship between erosion and weathering rates has largely been conducted in temperate climates with granitic bedrock. In tropical settings, the contribution of chemical mass loss to total denudation may approach, or even exceed, that of erosion. We report 10Be‐in‐quartz cosmogenic radionuclide and soil chemistry data from the Suckling‐Dayman Metamorphic Core Complex (SDMCC) in Papua New Guinea. Despite being exhumed at cm‐per‐year rates, its lower‐plate domed and striated morphology suggests minimal denudation, which is confirmed by our 10Be‐in‐quartz data (0.02–0.18 mm/yr). We suggest that rolling hinge‐style back‐rotation of the SDMCC's lower plate and the combination of a tropical climate and highly weatherable metabasalt bedrock have played a fundamental role in preserving the tectonic topography of this remarkable metamorphic core complex.

Large, Negative Atmospheric Carbon Monoxide Clumped Isotope Values Result From Kinetic Isotope Fractionation, Tracing OH• Reactivity

AbstractBecause of its global abundance and reactivity with hydroxyl radicals (OH•), tropospheric carbon monoxide indirectly impacts the lifetimes of other OH•‐reactive gases, in particular methane and reactive hydrocarbons. The origin and chemistry of atmospheric CO have been studied using stable isotopes. Both 13CO and C18O undergo isotopic fractionation during its main chemical loss reaction, CO + OH•. The kinetic isotope effect (KIE) for 13CO is mass dependent, with a value of ∼5‰; 12CO reacts faster than 13CO with OH. Whereas C18O + OH• exhibits an inversely mass dependent KIE ∼−10‰. We hypothesize these KIEs result in a relative depletion of 13C18O, a CO clumped isotope. To test this, we collected CO from air samples on Long Island, NY, and discovered a −3 to −8‰ difference in the clumped isotope ratio, Δ31, relative to a random distribution of 13C and 18O in CO. A clear negative trend between [CO] and Δ31 is driven by two factors: (a) the atmospheric addition of CO from either a primary or secondary source with a Δ31 of ∼0‰ and (b) the continuing reaction of CO with OH•, leaving the remaining CO pool relatively depleted in 13C18O. This is analogous to the mechanism that determines CO Δ17O values. This study is among the first to show clumped isotope fractionation resulting from atmospheric chemistry and not thermal equilibration, which may inform the identification of clumped isotope KIEs in other atmospheric trace gases. These first Δ31 observations motivate future experimental and observational studies targeted at characterizing the clumped isotopes of CO sources, background CO, and experimentally fractionated CO.

Accordion-like multilayered titanium nitride enables FeN4-O axial coordination of iron phthalocyanine as efficient catalysts for oxygen reduction reaction

The susceptibility of MXenes to oxidation leads to rapid chemical degradation and functional loss, and hence limits their diverse applications. In this study, we develop a scalable strategy to transform blocky, condensed titanium nitride (TiN) into accordion-like leafy titanium nitride (M-TiN), which exhibits enhanced chemical stability and an increased surface area. When functionalized with iron phthalocyanine (FePc), the resulting M-TiN/FePc composite displays a remarkable electrocatalytic activity towards the oxygen reduction reaction (ORR) due to the formation of FeN4-O axial coordination and a low-to-intermediate Fe spin state, as confirmed by spectroscopy and magnetic measurements. This leads to electron filling in the antibonding orbitals composed of Fe 3dz2 and O2 π* orbitals, significantly improving O2 activation and ORR activity. Significantly, with the M-TiN/FePc composite as the air cathode catalyst, a zinc-air battery achieves a superior power density of 270.31 mW cm−2 and enhanced cyclability compared to that with commercial Pt/C. Results from this study highlight the significance of morphological engineering of TiN in regulating the atomic configuration of adsorbed metal active centers and hence their catalytic activity, in particular, in harsh oxidative conditions.

Preparation and InVitro Evaluation of Protective Effects of Quercetin-Loaded Solid Lipid Nanoparticles on Human Hair Against UV-B Radiation.

The aim of this study was to investigate the protective effect of quercetin loaded on solid lipid nanoparticles (SLN) in protecting human hair from ultraviolet-B (UV-B) light invitro. In this study, solvent-emulsified diffusion method was used to fabricate nanoparticle formulations and then particle size, loading, and drug release tests were performed from different formulations. Variables include oily part proportion, liquid to solid oil part ratio, and surfactant to lipid ratio. The optimal formulation was prepared by examining the eight formulations and optimizing them. Six groups of hair with different treatments were exposed to UV light for 600 h and the changes were investigated by examining four factors: RMS (root mean square average, the microscopic profile peaks and valleys), peak to valley roughness, the amount of chemical changes by Fourier transform infrared spectroscopy (FTIR), and the amount of protein loss. The selected formulation had a suitable particle size, loading percent, and release rate for penetration to hair. Quercetin-loaded SLN controlled RMS factor, peak to valley roughness, and reduced chemical changes and protein loss compared to other treatments. The optimize formulation showed positive effects in protecting the hair strands from UV-B radiation.

An improved estimate of inorganic iodine emissions from the ocean using a coupled surface microlayer box model

Abstract. Iodine at the ocean's surface impacts climate and health by removing ozone (O3) from the troposphere both directly via ozone deposition to seawater and indirectly via the formation of iodine gases that are released into the atmosphere. Here we present a new box model of the ocean surface microlayer that couples oceanic O3 dry deposition to inorganic chemistry to predict inorganic iodine emissions. This model builds on the previous work of Carpenter et al. (2013), improving both chemical and physical processes. This new box model predicts iodide depletion in the top few micrometres of the ocean surface due to rapid chemical loss to ozone competing with replenishment from underlying water. From this box model, we produce parameterized equations for HOI and I2 emissions, which are implemented into the global chemical transport model GEOS-Chem along with an updated sea surface iodide climatology. Compared to the previous model, inorganic iodine emissions from some tropical waters decrease by as much as half, while higher-latitude emissions increase by a factor of ≫10. With these large local changes, global total inorganic iodine emissions increased by ∼49 % (2.99 to 4.48 Tg) compared to the previous parameterization. This results in a negligible change in average tropospheric OH (<0.2 %) and tropospheric methane lifetime (<0.2 %). The annual mean tropospheric O3 burden decreases (−1.5 % to 325 Tg); however, higher-latitude surface O3 concentrations decrease by as much as 20 %.

Stratospheric Chlorine Processing After the Unprecedented Hunga Tonga Eruption

AbstractFollowing the Hunga Tonga–Hunga Ha'apai (HTHH) eruption in January 2022, significant reductions in stratospheric hydrochloric acid (HCl) were observed in the Southern Hemisphere mid‐latitudes during the latter half of 2022, suggesting potential chlorine activation. The objective of this study is to comprehensively understand the loss of HCl in the aftermath of HTHH. Satellite measurements and a global chemistry‐climate model are employed for the analysis. We find strong agreement of 2022 anomalies between the modeled and the measured data. The observed tracer‐tracer relations between nitrous oxide (N2O) and HCl indicate a significant role of chemical processing in the observed HCl reduction, especially during the austral winter of 2022. Further examining the roles of chlorine gas‐phase and heterogeneous chemistry, we find that heterogeneous chemistry emerges as the primary driver for the chemical loss of HCl, and the reaction between hypobromous acid (HOBr) and HCl on sulfate aerosols is the dominant loss process.

Nonreciprocal response of electrically biased graphene-coated fiber.

Here, we theoretically investigate the nonreciprocal response of an electrically biased graphene-coated dielectric fiber. By electrically biasing the graphene coating along the fiber axis, the dynamic conductivity of graphene exhibits a nonsymmetric response with respect to the longitudinal component of guided-mode wave vectors. Consequently, the guided waves propagating in two opposite directions may encounter distinct propagation features. In this work, the electromagnetic properties, such as modal dispersion and some field distributions, are presented, and the strength of nonreciprocity is discussed for different parameters of graphene, such as its chemical potential and material loss. Furthermore, the influence of the radius of the fiber on the nonreciprocal response is investigated. We envision that such nonreciprocal optical fibers may find various potential applications in the THz regime.

One-step preparation of highly efficient adsorbents: Adsorption study of DMP on porous carbon macrobody based on sodium alginate

Porous carbon is a carbon material with a high surface area and abundant pore structure, holding extensive potential applications in the adsorption field. However, current porous carbon materials are complicated to prepare, and most are in powder form, making them difficult to separate from water after adsorption and prone to secondary pollution. This study uses sodium alginate (SA) as a precursor and K2CO3 one-step method to prepare sodium alginate-based macromaterials that can skillfully solve the above problems and explore its adsorption kinetics and thermodynamic characteristics for dimethyl phthalate (DMP). This study's meticulous control of experimental details enabled the fabrication of macroscopic materials. The appropriate temperature and activator blending ratio are critical to material agglomeration. (At 800 °C in a small ceramic boat, macroscopic material C800–2 was prepared with an activator ratio of K2CO3: sodium alginate at 2:1 and under low acid concentration acid washing (0.2 mol/L HCl)). Excessive pyrolysis temperature can lead to severe chemical bond loss, potentially preventing material agglomeration. Excessive doping of the activator may result in carbon framework collapse. While maintaining the macroscopic structure, C800–2 enhanced a 3.8-fold increase in total pore volume and a 4.6-fold increase in surface area. Moreover, at 313 K, its saturated adsorption of DMP reached an impressive 614.98 mg/g. C800–2 material exhibits excellent interference resistance and regeneration capability. The study achieves one-step fabrication of macroscopic materials while retaining superior adsorption performance, providing fundamental data for material engineering applications.

Interpreting Geostationary Environment Monitoring Spectrometer (GEMS) geostationary satellite observations of the diurnal variation in nitrogen dioxide (NO2) over East Asia

Abstract. Nitrogen oxide radicals (NOx≡NO+NO2) emitted by fuel combustion are important precursors of ozone and particulate matter pollution, and NO2 itself is harmful to public health. The Geostationary Environment Monitoring Spectrometer (GEMS), launched in space in 2020, now provides hourly daytime observations of NO2 columns over East Asia. This diurnal variation offers unique information on the emission and chemistry of NOx, but it needs to be carefully interpreted. Here we investigate the drivers of the diurnal variation in NO2 observed by GEMS during winter and summer over Beijing and Seoul. We place the GEMS observations in the context of ground-based column observations (Pandora instruments) and GEOS-Chem chemical transport model simulations. We find good agreement between the diurnal variations in NO2 columns in GEMS, Pandora, and GEOS-Chem, and we use GEOS-Chem to interpret these variations. NOx emissions are 4 times higher in the daytime than at night, driving an accumulation of NO2 over the course of the day, offset by losses from chemistry and transport (horizontal flux divergence). For the urban core, where the Pandora instruments are located, we find that NO2 in winter increases throughout the day due to high daytime emissions and increasing NO2/NOx ratio from entrainment of ozone, partly balanced by loss from transport and with a negligible role of chemistry. In summer, by contrast, chemical loss combined with transport drives a minimum in the NO2 column at 13:00–14:00 local time (LT). Segregation of the GEMS data by wind speed further demonstrates the effect of transport, with NO2 in winter accumulating throughout the day at low winds but flat at high winds. The effect of transport can be minimized in summer by spatially averaging observations over the broader metropolitan scale, under which conditions the diurnal variation in NO2 reflects a dynamic balance between emission and chemical loss.

Artificial-weathering test requirements for fire-retardant-treated wood to reproduce optimal chemical retention and moisture conditions

Despite the increasing outdoor use of fire-retardant-treated wood, methods for predicting its service life remain poorly established. With the aim of establishing a method to predict chemical losses from fire-retardant-treated (FRT) wood caused by humid atmospheres and rain outdoors, this study examined the preferable conditions for artificial-weathering tests and demonstrated the acceleration coefficients in these tests (i.e., the ratio of equivalent time to reach the same retention of chemicals in artificial weathering and outdoors) based on the EN927-6 standard. To determine the moisture absorption and desorption levels of FRT exposed to outdoor conditions, an outdoor exposure experiment was conducted. The moisture content was higher in the FRT wood than in untreated wood, regardless of the type of coating, and ranged between 11% (in March) and 50% (in September) of the untreated wood’s weight. EN927-6 artificial weathering tests were performed on two groups of specimens with initial moisture contents of 0% and 25%. Retention rates of fire-retardant chemicals after a 2520-h test were compared with those retrieved from 4-year outdoor exposure reported elsewhere. Comparison of these two experiments demonstrated that the acceleration coefficients were 4.1–11.3 in the case of specimens with 0% initial moisture content and 5.1–11.4 in the case of specimens with 25% initial moisture content. The higher initial moisture content produced a more uniform acceleration coefficient. Nevertheless, larger acceleration coefficients were derived from specimens with penetrating or semi-film-forming coatings in both cases. The relationships between the uniformity of this acceleration coefficient and the initial moisture content are discussed from the moisture absorption experiment under constant temperature and humidity and under condensation conditions.

Insights into the effect of operating parameters and hydrodynamics on hydrolysis reaction in Copper–Chlorine thermochemical water splitting cycle for hydrogen production: Modelling and experimental validation

Copper–Chlorine (Cu–Cl) thermochemical cycle is being explored as one of the promising technologies for large scale production of clean hydrogen from water using nuclear or renewable energy. In this method, water splitting is achieved through a series of reactions in a loop producing only hydrogen and oxygen with complete recycle of all the intermediate copper and chlorine compounds. The first step of the cycle is the hydrolysis reaction wherein steam reacts with solid CuCl2 to form solid Cu2OCl2 (copper oxychloride) and HCl gas. The products enter the subsequent steps of the cycle and are recycled back to complete the loop. Multiple side reactions in the hydrolysis step result in reduced yield and loss of chemicals from the cycle. Efficient reactor design and optimal operating conditions of hydrolysis reactor is imperative towards achieving sustained closed loop operation and reducing the energy demand of Cu–Cl cycle. This paper presents a mathematical model for the simulation of hydrolysis reaction in a bubbling fluidized bed reactor. The one-dimensional model is developed based on modified two-phase theory of fluidization and is coupled with kinetics of multiple side reactions to investigate the effect of operating parameters and hydrodynamics on the conversion and yield of Cu2OCl2. The model results are validated with experimental data in 50 mm and 100 mm semi-batch fluidized bed reactors. The developed model clearly brings out the effect of different process parameters for process optimization and scale-up of the hydrolysis reactor for efficient integration in the cycle.

Bacteria in clouds biodegrade atmospheric formic and acetic acids

Abstract. Formic and acetic acids are major organic species in cloud water and affect precipitation acidity. In atmospheric models, their losses are limited to chemical oxidation in the gas and aqueous phases and deposition processes. Previous lab studies suggest that these acids can be efficiently biodegraded in water by atmospherically relevant bacteria. However, the importance of biodegradation as a loss process in the atmospheric multiphase system has not been fully assessed. We implemented biodegradation as a sink of formic and acetic acids in a detailed atmospheric multiphase chemistry model. In our model, biodegradation is considered in 0.1 % of cloud droplets according to atmospheric bacteria concentrations of 0.1 cm−3. We predict that up to 20 ppt h−1 formic acid and 5 ppt h−1 acetic acid are biodegraded. This translates into a concentration change of 20 % and 3 % in addition to that caused by chemical losses. Our sensitivity studies suggest that acetic acid is most efficiently biodegraded at pH > 5, whereas biodegradation is least efficient for formic acid under such conditions. This trend can be explained by the fact that formic acid partitions more efficiently into the aqueous phase due to its higher Henry's law constant (KH,eff(HCOOH)=2×105 M atm−1 vs. KH,eff(CH3COOH)=3×104 M atm−1 at pH = 5). Therefore, under such conditions, formic acid evaporates less efficiently from bacteria-free droplets, resulting in less formic acid in the gas phase for dissolution bacteria-containing droplets to replenish biodegraded acid. Our analysis demonstrates that previous estimates of the importance of atmospheric biodegradation were often biased high as they did not correctly account for such uptake limitation in bacteria-containing droplets. The results suggest that, under specific conditions, biological processes can significantly affect atmospheric composition and concentrations in particular volatile, moderately soluble organics.

Assessing acetone for the GISS ModelE2.1 Earth system model

Abstract. Acetone is an abundant volatile organic compound (VOC) in the atmosphere, with important influences on ozone and oxidation capacity. Direct sources include chemical production from other VOCs and anthropogenic emissions, terrestrial vegetation, biomass-burning emissions, and ocean production. Sinks include chemical loss, deposition onto the land surface, and ocean uptake. Acetone also has a lifetime that is long enough to allow transport and reactions with other compounds remote from its sources. The NASA Goddard Institute for Space Studies (GISS) Earth system model ModelE2.1 simulates a variety of Earth system interactions. Previously, acetone had a very simplistic representation in the ModelE chemical scheme. This study assesses a more sophisticated acetone scheme in which acetone is a full 3-dimensional tracer with explicit sources, sinks, and atmospheric transport. We first evaluate the new global acetone budget in the context of past literature. Estimated source and sink fluxes fall within the range of previous models, although total atmospheric burden and lifetime are at the lower end of the published literature. Acetone's new representation in ModelE2.1 also results in more realistic spatial and vertical distributions, which we compare against previous models and field observations. The seasonality of acetone-related processes was also studied in conjunction with field measurements, and these comparisons show promising agreement but also shortcomings at high-emission urban locations, where the model's resolution is too coarse to capture the true behavior. Finally, we conduct a variety of sensitivity studies that explore the influence of key parameters on the acetone budget and its global distribution. An impactful finding is that the production of acetone from precursor hydrocarbon oxidation has strong leverage on the overall chemical source, indicating the importance of accurate molar yields. Overall, our implementation is one that corroborates with previous studies and marks a significant improvement in the development of the acetone tracer in GISS ModelE2.1.

Changes in factor profiles deriving from photochemical losses of volatile organic compounds: Insight from daytime and nighttime positive matrix factorization analyses

Substantial effects of photochemical reaction losses of volatile organic compounds (VOCs) on factor profiles can be investigated by comparing the differences between daytime and nighttime dispersion-normalized VOC data resolved profiles. Hourly speciated VOC data measured in Shijiazhuang, China from May to September 2021 were used to conduct study. The mean VOC concentration in the daytime and at nighttime were 32.8 and 36.0 ppbv, respectively. Alkanes and aromatics concentrations in the daytime (12.9 and 3.08 ppbv) were lower than nighttime (15.5 and 3.63 ppbv), whereas that of alkenes showed the opposite tendency. The concentration differences between daytime and nighttime for alkynes and halogenated hydrocarbons were uniformly small. The reactivities of the dominant species in factor profiles for gasoline emissions, natural gas and diesel vehicles, and liquefied petroleum gas were relatively low and their profiles were less affected by photochemical losses. Photochemical losses produced a substantial impact on the profiles of solvent use, petrochemical industry emissions, combustion sources, and biogenic emissions where the dominant species in these factor profiles had high reactivities. Although the profile of biogenic emissions was substantially affected by photochemical loss of isoprene, the low emissions at nighttime also had an important impact on its profile. Chemical losses of highly active VOC species substantially reduced their concentrations in apportioned factor profiles. This study results were consistent with the analytical results obtained through initial concentration estimation, suggesting that the initial concentration estimation could be the most effective currently available method for the source analyses of active VOCs although with uncertainty.

Missing Measurements of Sesquiterpene Ozonolysis Rates and Composition Limit Understanding of Atmospheric Reactivity.

Emissions of biogenic reactive carbon significantly influence atmospheric chemistry, contributing to the formation and destruction of secondary pollutants, such as secondary organic aerosol and ozone. While isoprene and monoterpenes are a major fraction of emissions and have been extensively studied, substantially less is known about the atmospheric impacts of higher-molecular-weight terpenes such as sesquiterpenes. In particular, sesquiterpenes have been proposed to play a significant role in ozone chemical loss due to the very high ozone reaction rates of certain isomers. However, relatively little data are available on the isomer-resolved composition of this compound class or its role in ozone chemistry. This study examines the chemical diversity of sesquiterpenes and availability of ozone reaction rate constants to evaluate the current understanding of their ozone reactivity. Sesquiterpenes are found to be highly diverse, with 72 different isomers reported and relatively few isomers that contribute a large mass fraction across all studies. For the small number of isomers with known ozone reaction rates, estimated rates may be 25 times higher or lower than measurements, indicating that estimated reaction rates are highly uncertain. Isomers with known ozone reaction rates make up approximately half of the mass of sesquiterpenes in concentration and emission measurements. Consequently, the current state of the knowledge suggests that the total ozone reactivity of sesquiterpenes cannot be quantified without very high uncertainty, even if isomer-resolved composition is known. These results are in contrast to monoterpenes, which are less diverse and for which ozone reaction rates are well-known, and in contrast to hydroxyl reactivity of monoterpenes and sesquiterpenes, for which reaction rates can be reasonably well estimated. Improved measurements of a relatively small number of sesquiterpene isomers would reduce uncertainties and improve our understanding of their role in regional and global ozone chemistry.

Improved simulations of biomass burning aerosol optical properties and lifetimes in the NASA GEOS Model during the ORACLES-I campaign

Abstract. In order to improve aerosol representation in the NASA Goddard Earth Observing System (GEOS) model, we evaluated simulations of the transport and properties of aerosols from southern African biomass burning sources that were observed during the first deployment of the NASA ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) field campaign in September 2016. An example case study of 24 September was analyzed in detail, during which aircraft-based in situ and remote sensing observations showed the presence of a multi-layered smoke plume structure with significant vertical variation in single scattering albedo (SSA). Our baseline GEOS simulations were not able to represent the observed SSA variation or the observed organic aerosol-to-black-carbon ratio (OA : BC). Analyzing the simulated smoke age suggests that the higher-altitude, less absorbing smoke plume was younger (∼4 d), while the lower-altitude and more absorbing smoke plume was older (∼7 d). We hypothesize a chemical or microphysical loss process exists to explain the change in aerosol absorption as the smoke plume ages, and we apply a simple loss rate to the model hydrophilic biomass burning OA to simulate this process. We also utilized the ORACLES airborne observations to better constrain the simulation of aerosol optical properties, adjusting the assumed particle size, hygroscopic growth, and absorption. Our final GEOS model simulation with additional OA loss and updated optics showed better performance in simulating aerosol optical depth (AOD) and SSA compared to independent ground- and space-based retrievals for the entire month of September 2016, including the Ozone Monitoring Instrument (OMI) Aerosol Index. In terms of radiative implications of our model adjustments, the final GEOS simulation suggested a decreased atmospheric warming of about 10 % (∼2 W m−2) over the southeastern Atlantic region and above the stratocumulus cloud decks compared to the model baseline simulations. These results improve the representation of the smoke age, transport, and optical properties in Earth system models.