Effect of Humidity on the Reactive Uptake of Ammonia and Dimethylamine by Nitrogen-Containing Secondary Organic Aerosol

This study investigated the uptake of ammonia (NH3) by secondary organic aerosol (SOA) particles generated via limonene photooxidation or ozonolysis as well as the uptake of dimethylamine (DMA) by limonene ozonolysis, α-cedrene photooxidation, or toluene photooxidation SOA in an environmental chamber between 0–50% relative humidity. In addition to the acid-base equilibrium uptake, NH3 and DMA can react with SOA carbonyl compounds converting them into nitrogen-containing organic compounds (NOCs). The effective reactive uptake coefficients for the formation of NOCs from ammonia were measured on the order of 10−5. The observed DMA reactive uptake coefficients ranged from 10−5 to 10−4. Typically, the reactive uptake coefficient decreased with increasing relative humidity. This is consistent with NOC formation by a condensation reaction between NH3 or DMA with SOA, which produces water as a product. Ammonia is more abundant in the atmosphere than amines. However, the larger observed reactive uptake coefficient suggests that amine uptake may also be a potential source of organic nitrogen in particulate matter.

Investigation of the behavior of tropospheric relevant compounds at the interface gas/organic acid aerosols: An ONIOM QM/MM study

<p>The uptake of atmospheric gaseous oxidant such as O<sub>3</sub> or the ROx (OH, HO<sub>2</sub>, RO<sub>2</sub>) family, have a strong impact on the oxidative capacity of the atmosphere. [1], [2] Last decade, few studies have been carried out on the uptake of such compounds on atmospheric aerosol. However, the large variety of organic compounds provides uptake coefficients with a wide range of order of magnitude. [3], [4] Furthermore, the uptake resulting from the combination of different processes (mass accommodation, bulk diffusion, reactivity), the detailed understanding of such a process is not always accessible through experiments. Theoretical tools such as quantum mechanics (QM) combined with Molecular Mechanics (MM) is one way to investigate separately the different processes.</p><p>The ONIOM hybrid QM/MM method [5] allows to study the reactivity of few molecules in a large system. In our group, a methodology using this computational method have been developed in order to estimate the reactive uptake of gaseous compounds onto organic aerosol particles. In this presentation, reactive uptake of HO<sub>2</sub> and O<sub>3</sub> onto glutaric acid and oleic acid aerosols respectively will be discussed. Comparisons will be addressed with gas phase theoretical reaction rates and with experimental data.</p><p><em>We acknowledge support by the French government through the Program “Investissement d'avenir” through the Labex CaPPA (contract ANR-11-LABX-0005-01) and I-SITE ULNE project OVERSEE (contract ANR-16-IDEX-0004), CPER CLIMIBIO (European Regional Development Fund, Hauts de France council, French Ministry of Higher Education and Research) and French national supercomputing facilities (grants DARI x2016081859 and A0050801859).</em></p><p> </p><p>References</p><p>[1]          H. L. Macintyre and M. J. Evans, “Parameterisation and impact of aerosol uptake of HO2 on a global tropospheric model,” Atmos. Chem. Phys., vol. 11, no. 21, pp. 10965–10974, Nov. 2011, doi: 10.5194/acp-11-10965-2011.</p><p>[2]          M. Zeng and K. R. Wilson, “Efficient Coupling of Reaction Pathways of Criegee Intermediates and Free Radicals in the Heterogeneous Ozonolysis of Alkenes,” The Journal of Physical Chemistry Letters, Jul. 2020, doi: 10.1021/acs.jpclett.0c01823.</p><p>[3]          P. S. J. Lakey, I. J. George, L. K. Whalley, M. T. Baeza-Romero, and D. E. Heard, “Measurements of the HO2 Uptake Coefficients onto Single Component Organic Aerosols,” Environ. Sci. Technol., vol. 49, no. 8, pp. 4878–4885, Apr. 2015, doi: 10.1021/acs.est.5b00948.</p><p>[4]          M. Mendez, N. Visez, S. Gosselin, V. Crenn, V. Riffault, and D. Petitprez, “Reactive and Nonreactive Ozone Uptake during Aging of Oleic Acid Particles,” J. Phys. Chem. A, vol. 118, no. 40, pp. 9471–9481, Oct. 2014, doi: 10.1021/jp503572c.</p><p>[5]          L. W. Chung et al., “The ONIOM Method and Its Applications,” Chem. Rev., vol. 115, no. 12, pp. 5678–5796, Jun. 2015, doi: 10.1021/cr5004419.</p>

Experimental reaction rates constrain estimates of ozone response to calcium carbonate geoengineering

Stratospheric solar geoengineering (SG) would impact ozone by heterogeneous chemistry. Evaluating these risks and methods to reduce them will require both laboratory and modeling work. Prior model-only work showed that CaCO3 particles would reduce, or even reverse ozone depletion. We reduce uncertainties in ozone response to CaCO3 via experimental determination of uptake coefficients and model evaluation. Specifically, we measure uptake coefficients of HCl and HNO3 on CaCO3 as well as HNO3 and ClONO2 on CaCl2 at stratospheric temperatures using a flow tube setup and a flask experiment that determines cumulative long-term uptake of HCl on CaCO3. We find that particle ageing causes significant decreases in uptake coefficients on CaCO3. We model ozone response incorporating the experimental uptake coefficients in the AER-2D model. With our new empirical reaction model, the global mean ozone column is reduced by up to 3%, whereas the previous work predicted up to 27% increase for the same SG scenario. This result is robust under our experimental uncertainty and many other assumptions. We outline systematic uncertainties that remain and provide three examples of experiments that might further reduce uncertainties of CaCO3 SG. Finally, we highlight the importance of the link between experiments and models in studies of SG.

Development and application of the WRFDA-Chem three-dimensional variational (3DVAR) system: aiming to improve air quality forecasting and diagnose model deficiencies

To improve the operational air quality forecasting over China, a new aerosol or gas-phase pollutants assimilation capability is developed within the WRFDA system using the three-dimensional variational (3DVAR) algorithm. In this first application, the interface for the MOSAIC (Model for Simulating Aerosol Interactions and Chemistry) aerosol scheme is built with the potential for flexible extension. Based on the new WRFDA-Chem system, five experiments assimilating different surface observations, including PM2.5, PM10, SO2, NO2, O3, and CO, are conducted for January 2017 along with a control experiment without data assimilation (DA). Results show that the WRFDA-Chem system evidently improves the air quality forecasting. From the analysis aspect, the assimilation of surface observations reduces the bias and RMSE in the initial condition (IC) remarkably; from the forecast aspect, better forecast performances are acquired up to 24 h, in which the experiment assimilating the six pollutants simultaneously displays the best forecast skill overall. With respect to the impact of the DA cycling frequency, the responses toward IC updating are found to be different among the pollutants. For PM2.5, PM10, SO2, and CO, the forecast skills increase with the DA frequency. For O3, although improvements are acquired at the 6 h cycling frequency, the advantage of more frequent DA could be consumed by the disadvantages of the unbalanced photochemistry (due to inaccurate precursor NOx ∕ VOC (volatile organic compound) ratios) or the changed titration process (due to changed NO2 concentrations but not NO) from assimilating the existing observations (only O3 and NO2, but no VOC and NO). As yet the finding is based on the 00:00 UTC forecast for this winter season only, and O3 has strong diurnal and seasonal variations. More experiments should be conducted to draw further conclusions. In addition, considering one aspect (IC) in the model is corrected by DA, the deficiencies of other aspects (e.g., chemical reactions) could be more evident. This study explores the model deficiencies by investigating the effects of assimilating gaseous precursors on the forecast of related aerosols. Results show that the parameterization (uptake coefficients) in the newly added sulfate–nitrate–ammonium (SNA)-relevant heterogeneous reactions in the model is not fully appropriate although it best simulates observed SNA aerosols without DA; since the uptake coefficients were originally tuned under the inaccurate gaseous precursor scenarios without DA, the biases from the two aspects (SNA reactions and IC DA) were just compensated. In future chemistry development, parameterizations (such as uptake coefficients) for different gaseous precursor scenarios should be adjusted and verified with the help of the DA technique. According to these results, DA ameliorates certain aspects by using observations as constraints and thus provides an opportunity to identify and diagnose the model deficiencies; it is useful especially when the uncertainties of various aspects are mixed up and the reaction paths are not clearly revealed. In the future, besides being used to improve the forecast through updating IC, DA could be treated as another approach to explore necessary developments in the model.

Development and application of the WRFDA-Chem 3DVAR system: aiming to improve air quality forecast and diagnose model deficiencies

To improve the operational air quality forecasting over China, a new aerosol/gas phase pollutants assimilation capability is developed within the WRFDA system using 3DVAR algorithm. In this first application, the interface for MOSAIC aerosol scheme is built with flexible extending potentials. Based on the new WRFDA-Chem system, five experiments assimilating different surface observations, including PM2.5, PM10, SO2, NO2, O3, and CO are conducted for January 2017 along with a control experiment without DA. Results exhibit that the WRFDA-Chem system evidently improves the air quality forecasting. On the analysis aspect, the assimilation of surface observations reduces the bias and RMSE in the initial condition (IC) remarkably; on the forecast aspect, better forecast performances are acquired up to 24-h, in which the experiment assimilating the six pollutants simultaneously displays the best forecast skill overall. With respect to the impact of DA cycling frequency, the responses toward IC updating are found out to be different among the pollutants. For PM2.5, PM10, SO2 and CO, the forecast skills increase with the DA frequency; for O3, although improvements are acquired at the 6-h cycling frequency, the advantage of more frequent DA could be consumed by the disadvantage of unbalanced photochemistry (due to inaccurate precursor NOx/VOC ratios) from assimilating the existing observations (only O3 and NO2, but no VOC). Considering after one aspect (IC) in the model is corrected by DA, the deficiencies from other aspects (e.g., chemical reactions) could be more evident, this study further explores the model deficiencies by investigating the effects of assimilating gaseous precursors on the forecast of related aerosols. Results exhibit that the parameterization (uptake coefficients) in the newly added Sulfate-Nitrate-Ammonium (SNA) relevant heterogeneous reactions in the model are not fully appropriate although it best simulates observed SNA aerosols without DA; since the uptake coefficients were originally tuned under the inaccurate gaseous precursor scenarios without DA, the biases from the two aspects (SNA reactions and IC DA) were just compensated. In the future chemistry development, parameterizations (such as uptake coefficients) for different gaseous precursor scenarios should be adjusted and verified with the help of DA technique. According to these results, DA ameliorates certain aspects by using observation as constraints, and thus provides an opportunity to identify and diagnose the model deficiencies; it is useful especially when the uncertainties of various aspects are mixed up and the reaction paths are not clearly revealed. In the future, besides being used to improve the forecast through updating IC, DA could be treated as another approach to explore necessary developments in the model.