Modelling the photochemical formation of high H2O2 concentrations and secondary sulfate observed during winter haze periods in the NCP

2020 ◽  
Author(s):  
Andreas Tilgner ◽  
Erik Hans Hoffmann ◽  
Lin He ◽  
Bernd Heinold ◽  
Can Ye ◽  
...  
Keyword(s):  
Air Pollution ◽  
Gas Phase ◽  
Aqueous Phase ◽  
Photochemical Reactions ◽  
Data Availability ◽  
Phase Reaction ◽  
Aerosol Composition ◽  
Chemistry Research ◽  
The Impact

<p>During winter, the North China Plain (NCP) is frequently characterized by severe haze conditions connected with extremely high PM2.5 and NOx concentrations, i.e. strong air pollution. The NCP is one of the most populated regions worldwide where haze periods have direct health effects. Tropospheric haze particles are a complex multiphase and multi-component environment, in which multiphase chemical processes are able to alter the chemical aerosol composition and deduced physical aerosol properties and can strongly contribute to air pollution. Despite many past investigations, the chemical haze processing is still uncertain and represents a challenge to atmospheric chemistry research. Recent NCP studies during autumn/winter 2017 haze periods have revealed unexpected high H<sub>2</sub>O<sub>2</sub> concentrations of about 1 ppb suggesting H<sub>2</sub>O<sub>2</sub> as a potential contributor to secondary PM2.5 mass, e.g., due to sulfur(IV) oxidation. However, the multiphase H<sub>2</sub>O<sub>2</sub> formation under such NOx concentrations is still unclear. Therefore, the present study aimed at the examination of potential multiphase H<sub>2</sub>O<sub>2</sub> formation pathways, and the feedback on sulfur oxidation.</p><p>Multiphase chemistry simulations of a measurement campaign in the NCP are performed with the box model SPACCIM. The multiphase chemistry model within SPACCIM contains the gas-phase mechanism MCMv3.2 and the aqueous-phase mechanism CAPRAM4.0 together with both its aromatics module CAPRAM-AM1.0 and its halogen module CAPRAM-HM2.1. Furthermore, based on available literature data, the multiphase chemistry mechanism is extended considering further multiphase formation pathways of HONO and an advanced HOx mechanism scheme enabling higher in-situ H<sub>2</sub>O<sub>2</sub> formations in haze particles. The simulations have been performed for three periods characterized by high H<sub>2</sub>O<sub>2</sub> concentrations, high RH and PM2.5 conditions and high measurement data availability. Several sensitivity runs have been performed examining the impact of the soluble transition metal ion (TMI) content on the predicted H<sub>2</sub>O<sub>2</sub> formation.</p><p>Simulations with the improved multiphase chemistry mechanism shows a good agreement of the modelled H<sub>2</sub>O<sub>2</sub> concentrations with field data. The modelled H<sub>2</sub>O<sub>2</sub> concentration shows a substantial dependency on the soluble TMI content. Higher soluble TMI contents result in higher H<sub>2</sub>O<sub>2</sub> concentrations demonstrating the strong influence of TMI chemistry in haze particles on H<sub>2</sub>O<sub>2</sub> formation. The analysis of the chemical production and sink fluxes reveals that a huge fraction of the multiphase HO<sub>2</sub> radicals and nearly all of the subsequently formed reaction product H<sub>2</sub>O<sub>2</sub> is produced in-situ within the haze particles and does not origin from the gas phase. Further chemical analyses show that, during the morning hours, the aqueous-phase reaction of H<sub>2</sub>O<sub>2</sub> with S(IV) contributes considerably to S(VI) formation beside the HONO related formation of sulfuric acid by OH in the gas-phase.</p><p>Finally, a parameterization was developed to study the particle-phase H<sub>2</sub>O<sub>2</sub> formations as potential source with the global model ECHAM-HAMMOZ. The performed global modelling identifies an increase of gas-phase H<sub>2</sub>O<sub>2</sub> by a factor of 2.8 through the newly identified particle chemistry. Overall, the study demonstrated that photochemical reactions of HULIS and TMIs in particles are an important H<sub>2</sub>O<sub>2</sub> source leading to increased particle sulfate formation.</p>

The Impact of the Aqueous Phase Chemistry of HNO4 on Gas Phase Tropospheric Chemistry

2001 ◽  
Vol 32 ◽  
pp. 269-270
Author(s):  
J.E. WILLIAMS ◽  
F.J. DENTENER ◽  
A.R. van den BERG
Keyword(s):  
Gas Phase ◽  
Aqueous Phase ◽  
Tropospheric Chemistry ◽  
Phase Chemistry ◽  
The Impact

In situ analysis of gas phase reaction processes within monolithic catalyst supports by applying NMR imaging methods

2016 ◽  
Vol 273 ◽  
pp. 91-98 ◽  
Author(s):  
Jürgen Ulpts ◽  
Wolfgang Dreher ◽  
Lars Kiewidt ◽  
Miriam Schubert ◽  
Jorg Thöming
Keyword(s):  
Gas Phase ◽  
In Situ Analysis ◽  
Catalyst Supports ◽  
Nmr Imaging ◽  
Phase Reaction ◽  
Imaging Methods ◽  
Monolithic Catalyst ◽  
Gas Phase Reaction ◽  
Reaction Processes

scholarly journals Gaseous chemistry and aerosol mechanism developments for version 3.5.1 of the online regional model, WRF-Chem

2014 ◽  
Vol 7 (6) ◽  
pp. 2557-2579 ◽  
Author(s):  
S. Archer-Nicholls ◽  
D. Lowe ◽  
S. Utembe ◽  
J. Allan ◽  
R. A. Zaveri ◽  
...  
Keyword(s):  
Gas Phase ◽  
Chemical Mechanism ◽  
Reduced Form ◽  
Sea Spray ◽  
Wind Fields ◽  
Aerosol Composition ◽  
Aerosol Emission ◽  
Sea Spray Aerosol ◽  
The Impact ◽  
Phase Chemical

Abstract. We have made a number of developments to the Weather, Research and Forecasting model coupled with Chemistry (WRF-Chem), with the aim of improving model prediction of trace atmospheric gas-phase chemical and aerosol composition, and of interactions between air quality and weather. A reduced form of the Common Reactive Intermediates gas-phase chemical mechanism (CRIv2-R5) has been added, using the Kinetic Pre-Processor (KPP) interface, to enable more explicit simulation of VOC degradation. N2O5 heterogeneous chemistry has been added to the existing sectional MOSAIC aerosol module, and coupled to both the CRIv2-R5 and existing CBM-Z gas-phase schemes. Modifications have also been made to the sea-spray aerosol emission representation, allowing the inclusion of primary organic material in sea-spray aerosol. We have worked on the European domain, with a particular focus on making the model suitable for the study of nighttime chemistry and oxidation by the nitrate radical in the UK atmosphere. Driven by appropriate emissions, wind fields and chemical boundary conditions, implementation of the different developments are illustrated, using a modified version of WRF-Chem 3.4.1, in order to demonstrate the impact that these changes have in the Northwest European domain. These developments are publicly available in WRF-Chem from version 3.5.1 onwards.

scholarly journals Portable calibrator for NO based on the photolysis of N<sub>2</sub>O and a combined NO<sub>2</sub>∕NO∕O<sub>3</sub> source for field calibrations of air pollution monitors

2020 ◽  
Vol 13 (2) ◽  
pp. 1001-1018 ◽  
Author(s):  
John W. Birks ◽  
Andrew A. Turnipseed ◽  
Peter C. Andersen ◽  
Craig J. Williford ◽  
Stanley Strunk ◽  
...  
Keyword(s):  
Air Pollution ◽  
Gas Phase ◽  
Phase Reaction ◽  
Calibration Source ◽  
Transfer Standard ◽  
Mixing Ratios ◽  
Wide Range ◽  
New Instrument ◽  
Gas Cylinders ◽  
Better Than

Abstract. A highly portable calibration source of nitric oxide (NO) based on the photolysis of nitrous oxide (N2O) supplied by 8 or 16 g disposable cartridges is demonstrated to serve as an accurate and reliable transfer standard for the calibration of NO monitors in the field. The instrument provides output mixing ratios in the range 0–1000 ppb with a precision and accuracy better than the greater of 3 ppb or 3 % of the target NO mixing ratio over a wide range of environmental conditions of ambient temperature (8.5–35.0 ∘C), pressure (745–1015 mbar corresponding to 2.7–0.0 km of elevation), and relative humidity (0 %–100 % RH). The combination of the NO calibration source with a previously described ozone calibration source based on the photolysis of oxygen in air provides a new instrument capable of outputting calibrated mixing ratios of NO, ozone (O3), and nitrogen dioxide (NO2), where the NO2 is produced by the stoichiometric gas-phase reaction of NO with O3. The portable NO2/NO/O3 calibration source requires no external gas cylinders and can be used for calibrations of NO, NO2, and O3 instruments for mixing ratios up to 1000, 500, and 1000 ppb, respectively. This portable calibrator may serve as a convenient transfer standard for field calibrations of ozone and NOx air pollution monitors.

In-Situ Formation and Characterization of α-Si3N4 Whiskers from Nano Amorphous Si-N-C Powders

1994 ◽  
Vol 363 ◽  
Author(s):  
Ya-Li Li ◽  
Yong Liang ◽  
Zhuang-Qi Hu
Keyword(s):  
Gas Phase ◽  
Whisker Growth ◽  
Process Conditions ◽  
Phase Reaction ◽  
In Situ Formation ◽  
Amorphous Si ◽  
Xrd Techniques ◽  
Vs Mechanism

Abstractα-Si3N4 whiskers were formed from laser-synthesized nanoscale amorphous Si-N-C powders at 1873K under 1 atm N2. The as-formed whiskers were characterized by TEM, STEM, XRD techniques and the process conditions for the whisker growth were studied. The whiskers exhibit various morphologies such as the long thick straight, the prismatic, the ribbon-like, and knuckled whiskers. The gas phase reaction among N2, SiO, and CO gases leads to Si3N4 whisker growth on the pre-crystallized α-Si3N4 grains by the Vapor-Solid (VS) mechanism along specific crystal planes such as {1101}., which ensures an in-situ formation. No addition of other catalyst and the atomic combination of the elements in the Si-N-C powders ensure a high purity of the whiskers.

scholarly journals Evaluation of the daytime tropospheric loss of 2-methylbutanal

2021 ◽  
Author(s):  
María Asensio ◽  
María Antiñolo ◽  
Sergio Blázquez ◽  
José Albaladejo ◽  
Elena Jiménez
Keyword(s):  
Mass Spectrometry ◽  
Gas Phase ◽  
Degradation Products ◽  
Rate Coefficients ◽  
Oh Radicals ◽  
Phase Reaction ◽  
Gaseous Products ◽  
Flight Mass Spectrometry ◽  
Atmospheric Degradation ◽  
The Impact

Abstract. Saturated aldehydes, e.g. 2-methylbutanal (2MB, CH3CH2CH(CH3)C(O)H), are emitted into the atmosphere by several biogenic sources. The first step in the daytime atmospheric degradation of 2MB involves gas-phase reactions initiated by hydroxyl (OH) radicals, chlorine (Cl) atoms and/or sunlight. In this work, we report the rate coefficients for the gas-phase reaction of 2MB with OH (kOH) and Cl (kCl) together with the photolysis rate coefficient (J) in the ultraviolet solar actinic region in Valencia (Spain) at different times of the day. The temperature dependence of kOH was described in the 263–353 K range by the following Arrhenius expression: kOH(T)=(8.88±0.41)×10-12 exp[(331±14)/T] cm3 molecule-1 s-1. At 298 K, the reported kOH and kCl are (2.68±0.07)×10-11 cm3 molecule-1 s-1 and (2.16±0.16)×10-11 cm3 molecule-1 s-1. Identification and quantification of the gaseous products of the Cl-reaction and those from the photodissociation of 2MB were carried out in a smog chamber by different techniques (Fourier transform infrared spectroscopy, proton transfer time-of-flight mass spectrometry, and gas chromatography coupled to mass spectrometry). The formation and size distribution of secondary organic aerosols formed in the Cl-reaction was monitored by a fast mobility particle sizer spectrometer. A discussion on the relative importance of the first step in the daytime atmospheric degradation of 2MB is presented together with the impact of the degradation products in marine atmospheres.

scholarly journals Photodegradation of Riboflavin under Alkaline Conditions: What can Gas-Phase Photolysis Tell Us About What Happens in Solution?

2021 ◽  
Author(s):  
Natalie G.K. Wong ◽  
Chris Rhodes ◽  
Caroline E.H. Dessent
Keyword(s):  
Mass Spectrometry ◽  
Gas Phase ◽  
Direct Method ◽  
Photochemical Reactions ◽  
Solution Phase ◽  
Ionization Mass ◽  
Phase Reaction ◽  
Esi Ms ◽  
Alkaline Conditions ◽  
On Line

The application of electrospray ionization mass spectrometry (ESI-MS) as a direct method for detecting reactive intermediates is a technique of developing importance in the routine monitoring of solution-phase reaction pathways. Here, we utilize a novel on-line photolysis ESI-MS approach to detect the photoproducts of riboflavin in aqueous solution under mildly alkaline conditions. Riboflavin is a constituent of many food products, so its breakdown processes are of wide interest. Our on-line photolysis setup allows for solution-phase photolysis to occur within a syringe using UVA LEDs, immediately prior to being introduced into the mass spectrometer via ESI. Gas-phase photofragmentation studies via laser-interfaced mass spectrometry of deprotonated riboflavin, [RFH], the dominant solution-phase species under the conditions of our study, are presented alongside the solution-phase photolysis. The results obtained illustrate the extent to which gas-phase photolysis methods can inform our understanding of the corresponding solution-phase photochemistry. We determine that the solution-phase photofragmentation observed for [RFH] closely mirrors the gas-phase photochemistry, with the m/z 241 ion being the only major condensed-phase photoproduct. Further gas-phase photoproducts are observed at m/z 255, 212, and 145. The value of exploring both the gas- and solution-phase photochemistry to characterize photochemical reactions is discussed.

Satellite-derived shorelines reveal fascinating dynamics for the last three decades on Danube Delta coast

2021 ◽  
Author(s):  
Florin Tatui ◽  
Georgiana Anghelin ◽  
Sorin Constantin
Keyword(s):  
Satellite Images ◽  
High Energy ◽  
Data Availability ◽  
Danube Delta ◽  
Dune System ◽  
Temporal Scales ◽  
Wide Range ◽  
The Impact ◽  
Sentinel 2

&lt;p&gt;Shoreline, as the interface between the upper shoreface and the beach-dune system, is sensitive to all changes from both the underwater and sub-aerial parts of the beach at a wide range of temporal scales (seconds to decades), making it a good indicator for coastal health. While more traditional techniques of shoreline monitoring present some shortcomings (low temporal resolution for photointerpretation, reduced spatial extension for video-based techniques, high costs for DGPS in-situ data acquisition), freely available satellite images can provide information for large areas (tens/hundreds of km) at very good temporal scales (days).&lt;/p&gt;&lt;p&gt;We employed a shoreline detection workflow for the dynamic environment of the Danube Delta coast (Black Sea). We focused on an index-based approach using the Automated Water Extraction Index (AWEI). A fully automated procedure was deployed for data processing and the waterline was estimated at sub-pixel level with an adapted image thresholding technique. For validation purposes, 5 Sentinel-2 and 5 Landsat based results were compared with both in-situ (D)GPS measurements and manually digitized shoreline positions from very high-resolution satellite images (Pleiades &amp;#8211; 0.5 m and Spot 7 &amp;#8211; 1.5 m). The overall accuracy of the methodology, expressed as mean absolute error, was found to be of approximately 7.5 m for Sentinel-2 and 4.7 m for Landsat data, respectively.&lt;/p&gt;&lt;p&gt;More than 200 Landsat (5 and 8) and Sentinel-2 images were processed and the corresponding satellite-derived shorelines between 1990 and 2020 were analysed for the whole Romanian Danube Delta coast (130 km). This high number of shorelines allowed us the discrimination of different patterns of coastline dynamic and behaviour which could not have been possible using usual surveying techniques: the extent of accumulation areas induced by the 2005-2006 historical river floods, the impact of different high-energy storms and the subsequent beach recovery after these events, the alongshore movement of erosional processes in accordance with the dominant direction of longshore sediment transport, multi-annual differences in both erosional and accumulation trends. Moreover, a very important result of our analysis is the zonation of Danube Delta coast based on multi-annual trends of shoreline dynamics at finer alongshore spatial resolution than before. This has significant implications for future studies dealing with different scenarios of Danube Delta response to projected sea level rise and increased storminess.&lt;/p&gt;&lt;p&gt;The presented approach and resulting products offer optimal combination of data availability, accuracy and frequency necessary to meet the monitoring and management needs of the increasing number of stakeholders involved in the coastal zone protection activities.&lt;/p&gt;

Influence of in-cloud oxidation of organic compounds on tropospheric ozone

2021 ◽  
Author(s):  
Simon Rosanka ◽  
Rolf Sander ◽  
Bruno Franco ◽  
Catherine Wespes ◽  
Andreas Wahner ◽  
...  
Keyword(s):  
Gas Phase ◽  
Organic Compounds ◽  
Aqueous Phase ◽  
Phase Transfer ◽  
Sulfur Oxidation ◽  
Box Model ◽  
Atmospheric Models ◽  
Model Studies ◽  
Phase Chemistry ◽  
The Impact

&lt;p&gt;Large parts of the troposphere are affected by clouds, whose aqueous-phase chemistry differs significantly from gas-phase chemistry. Box-model studies have demonstrated that clouds influence the tropospheric oxidation capacity. However, most global atmospheric models do not represent this chemistry reasonably well and are largely limited to sulfur oxidation. Therefore, we have developed the J&amp;#252;lich Aqueous-phase Mechanism of Organic Chemistry (JAMOC), making a detailed in-cloud oxidation model of oxygenated volatile organic compounds (OVOCs) readily available for box as well as for regional and global simulations that are affordable with modern supercomputers. JAMOC includes the phase transfer of species containing up to ten carbon atoms, and the aqueous-phase reactions of a selection of species containing up to four carbon atoms, e.g., ethanol, acetaldehyde, glyoxal. The impact of in-cloud chemistry on tropospheric composition is assessed on a regional and global scale by performing a combination of box-model studies using the Chemistry As A Boxmodel Application (CAABA) and the global atmospheric model ECHAM/MESSy (EMAC). These models are capable to represent the described processes explicitly and integrate the corresponding ODE system with a Rosenbrock solver.&amp;#160;&lt;/p&gt;&lt;p&gt;Overall, the explicit in-cloud oxidation leads to a reduction of predicted OVOCs levels. By comparing EMAC's prediction of methanol abundance to spaceborne retrievals from the Infrared Atmospheric Sounding Interferometer (IASI), a reduction in EMAC's overestimation is observed in the tropics. Further, the in-cloud OVOC oxidation shifts the hydroperoxyl radicals (HO&lt;sub&gt;2&lt;/sub&gt;) production from the gas- to the aqueous-phase. As a result, the in-cloud destruction (scavenging) of ozone (O&lt;sub&gt;3&lt;/sub&gt;) by the superoxide anion (O&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt;) is enhanced and accompanied by a reduction in both sources and sinks of tropospheric O&lt;sub&gt;3&lt;/sub&gt; in the gas phase. By considering only the in-cloud sulfur oxidation by O&lt;sub&gt;3&lt;/sub&gt;, about 13 Tg a&lt;sup&gt;-1&lt;/sup&gt; of O&lt;sub&gt;3&lt;/sub&gt; are scavenged, which increases to 336 Tg a&lt;sup&gt;-1&lt;/sup&gt; when JAMOC is used. With the full oxidation scheme, the highest O&lt;sub&gt;3&lt;/sub&gt; reduction of 12 % is predicted in the upper troposphere/lower stratosphere (UTLS). Based on the IASI O&lt;sub&gt;3&lt;/sub&gt; retrievals, it is demonstrated that these changes in the free troposphere significantly reduce the modelled tropospheric O&lt;sub&gt;3&lt;/sub&gt; columns, which are known to be generally overestimated by global atmospheric models. Finally, the relevance of aqueous-phase oxidation of organics for ozone in hazy polluted regions will be presented. &amp;#160;&lt;/p&gt;

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