scholarly journals Attribution of modeled atmospheric sulfate and SO<sub>2</sub> in the Northern Hemisphere for June–July 1997

2006 ◽  
Vol 6 (12) ◽  
pp. 4723-4738 ◽  
Author(s):  
C. M. Benkovitz ◽  
S. E. Schwartz ◽  
M. P. Jensen ◽  
M. A. Miller
Keyword(s):  
Gas Phase ◽  
Aqueous Phase ◽  
Northern Hemisphere ◽  
Radiative Forcing ◽  
Transport Model ◽  
Atmospheric Particulate Matter ◽  
Phase Reaction ◽  
Formation Pathway ◽  
Cloud Properties ◽  
June July

Abstract. Anthropogenic sulfate aerosol is a major contributor to shortwave radiative forcing of climate change by direct light scattering and by perturbing cloud properties and to local concentrations of atmospheric particulate matter. Here we analyze results from previously published calculations with an Eulerian transport model for atmospheric sulfur species in the Northern Hemisphere in June–July, 1997 to quantify the absolute and relative contributions of specific source regions (North America, Europe, and Asia) and SO2-to-sulfate conversion mechanisms (gas-phase, aqueous-phase and primary sulfate) to sulfate and SO2 column burdens as a function of location and time. Although material emitted within a given region dominates the sulfate and SO2 column burden in that region, examination of time series at specific locations shows that material imported from outside can make a substantial and occasionally dominant contribution. Frequently the major fraction of these exogenous contributions to the sulfate column burden was present aloft, thus minimally impacting air quality at the surface, but contributing substantially to the burden and, by implication, to radiative forcing and diminution of surface irradiance. Although the dominant sulfate formation pathway in the domain as a whole is aqueous-phase reaction in clouds (62%), in regions with minimum opportunity for aqueous-phase reaction gas-phase oxidation is dominant, albeit with considerable temporal variability depending on meteorological conditions. These calculations highlight the importance of transoceanic transport of sulfate, especially at the western margins of continents under the influence of predominantly westerly transport winds.

scholarly journals Attribution of Modeled Atmospheric Sulfate and SO<sub>2</sub> in the Northern Hemisphere for June–July 1997

2006 ◽  
Vol 6 (3) ◽  
pp. 4023-4059
Author(s):  
C. M. Benkovitz ◽  
S. E. Schwartz ◽  
M. P. Jensen ◽  
M. A. Miller
Keyword(s):  
Gas Phase ◽  
Aqueous Phase ◽  
Northern Hemisphere ◽  
Radiative Forcing ◽  
Transport Model ◽  
Atmospheric Particulate Matter ◽  
Phase Reaction ◽  
Formation Pathway ◽  
Cloud Properties ◽  
June July

Abstract. Anthropogenic sulfate aerosol is a major contributor to shortwave radiative forcing of climate change by direct light scattering and by perturbing cloud properties and to local concentrations of atmospheric particulate matter. Here we analyze results from previously published calculations with an Eulerian transport model for atmospheric sulfur species in the Northern Hemisphere in June–July, 1997 to quantify the absolute and relative contributions of specific source regions (North America, Europe, and Asia) and SO2-to-sulfate conversion mechanisms (gas-phase, aqueous-phase and primary sulfate) to sulfate and SO2 column burdens as a function of location and time. Although material emitted within a given region dominates the sulfate and SO2 column burden in that region, examination of time series at specific locations shows that material imported from outside can make a substantial and occasionally dominant contribution. Frequently the major fraction of these exogenous contributions to the sulfate column burden was present aloft, thus minimally impacting air quality at the surface, but contributing substantially to the burden and, by implication, to radiative forcing and diminution of surface irradiance. Although the dominant sulfate formation pathway in the domain as a whole is aqueous-phase reaction in clouds (61.7%), in regions with minimum opportunity for aqueous-phase reaction gas-phase oxidation can be dominant, albeit with considerable temporal variability depending on meteorological conditions. These calculations highlight the importance of transoceanic transport of sulfate, especially at the western margins of continents under the influence of predominantly westerly transport winds.

scholarly journals DMS oxidation and sulfur aerosol formation in the marine troposphere: a focus on reactive halogen and multiphase chemistry

2018 ◽  
Vol 18 (18) ◽  
pp. 13617-13637 ◽  
Author(s):  
Qianjie Chen ◽  
Tomás Sherwen ◽  
Mathew Evans ◽  
Becky Alexander
Keyword(s):  
Gas Phase ◽  
Dimethyl Sulfide ◽  
Transport Model ◽  
Removal Rate ◽  
Sulfur Cycle ◽  
Phase Reaction ◽  
Aerosol Formation ◽  
Cloud Droplets ◽  
Sulfur Chemistry ◽  
Marine Troposphere

Abstract. The oxidation of dimethyl sulfide (DMS) in the troposphere and subsequent chemical conversion into sulfur dioxide (SO2) and methane sulfonic acid (MSA) are key processes for the formation and growth of sulfur-containing aerosol and cloud condensation nuclei (CCN), but are highly simplified in large-scale models of the atmosphere. In this study, we implement a series of gas-phase and multiphase sulfur oxidation mechanisms into the Goddard Earth Observing System-Chemistry (GEOS-Chem) global chemical transport model – including two important intermediates, dimethyl sulfoxide (DMSO) and methane sulphinic acid (MSIA) – to investigate the sulfur cycle in the global marine troposphere. We found that DMS is mainly oxidized in the gas phase by OH (66 %), NO3 (16 %) and BrO (12 %) globally. DMS + BrO is important for the model's ability to reproduce the observed seasonality of surface DMS mixing ratio in the Southern Hemisphere. MSA is mainly produced from multiphase oxidation of MSIA by OH(aq) (66 %) and O3(aq) (30 %) in cloud droplets and aerosols. Aqueous-phase reaction with OH accounts for only 12 % of MSA removal globally, and a higher MSA removal rate is needed to reproduce observations of the MSA ∕ nssSO42- ratio. The modeled conversion yield of DMS into SO2 and MSA is 75 % and 15 %, respectively, compared to 91 % and 9 % in the standard model run that includes only gas-phase oxidation of DMS by OH and NO3. The remaining 10 % of DMS is lost via deposition of intermediates DMSO and MSIA. The largest uncertainties for modeling sulfur chemistry in the marine boundary layer (MBL) are unknown concentrations of reactive halogens (BrO and Cl) and OH(aq) concentrations in cloud droplets and aerosols. To reduce uncertainties in MBL sulfur chemistry, we should prioritize observations of reactive halogens and OH(aq).

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

&lt;p&gt;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&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; concentrations of about 1&amp;#160;ppb suggesting H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; as a potential contributor to secondary PM2.5 mass, e.g., due to sulfur(IV) oxidation. However, the multiphase H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; formation under such NOx concentrations is still unclear. Therefore, the present study aimed at the examination of potential multiphase H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; formation pathways, and the feedback on sulfur oxidation.&lt;/p&gt;&lt;p&gt;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&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; formations in haze particles. The simulations have been performed for three periods characterized by high H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; 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&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; formation.&lt;/p&gt;&lt;p&gt;Simulations with the improved multiphase chemistry mechanism shows a good agreement of the modelled H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; concentrations with field data. The modelled H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; concentration shows a substantial dependency on the soluble TMI content. Higher soluble TMI contents result in higher H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; concentrations demonstrating the strong influence of TMI chemistry in haze particles on H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; formation. The analysis of the chemical production and sink fluxes reveals that a huge fraction of the multiphase HO&lt;sub&gt;2&lt;/sub&gt; radicals and nearly all of the subsequently formed reaction product H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; 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&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; with S(IV) contributes considerably to S(VI) formation beside the HONO related formation of sulfuric acid by OH in the gas-phase.&lt;/p&gt;&lt;p&gt;Finally, a parameterization was developed to study the particle-phase H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; formations as potential source with the global model ECHAM-HAMMOZ. The performed global modelling identifies an increase of gas-phase H&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; 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&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; source leading to increased particle sulfate formation.&lt;/p&gt;

scholarly journals Modeling of daytime HONO vertical gradients during SHARP 2009

2012 ◽  
Vol 12 (10) ◽  
pp. 27775-27819
Author(s):  
K. W. Wong ◽  
C. Tsai ◽  
B. Lefer ◽  
N. Grossberg ◽  
J. Stutz
Keyword(s):  
Boundary Layer ◽  
Gas Phase ◽  
Rural Areas ◽  
Transport Model ◽  
Vertical Transport ◽  
Formation Mechanisms ◽  
Aerosol Model ◽  
Formation Pathway ◽  
Sensitivity Studies ◽  
Urban And Rural Areas

Abstract. Nitrous Acid (HONO) acts as a major precursor of the hydroxyl radical (OH) in the urban atmospheric boundary layer in the morning and throughout the day. Despite its importance, HONO formation mechanisms are not yet completely understood. It is generally accepted that conversion of NO2 on surfaces in the presence of water is responsible for the formation of HONO in the nocturnal boundary layer, although the type of surface on which the mechanism occurs is still under debate. Recent observations of higher than expected daytime HONO concentrations in both urban and rural areas indicate the presence of unknown daytime HONO source(s). Various formation pathways in the gas-phase and on aerosol and ground surfaces have been proposed to explain the presence of daytime HONO. However, it is unclear which mechanism dominates and, in the cases of heterogeneous mechanisms, on which surfaces they occur. Vertical concentration profiles of HONO and its precursors can help in identifying the dominant HONO formation pathways. In this study, daytime HONO and NO2 vertical profiles, measured in three different height intervals (20–70 m, 70–130 m and 130–300 m) in Houston, TX during the 2009 Study of Houston Atmospheric Radical Precursors (SHARP) are analyzed using a one-dimensional (1-D) chemistry and transport model. Model results with various HONO formation pathways suggested in the literature are compared to the the daytime HONO and HONO/NO2 ratios observed during SHARP. The best agreement of HONO and HONO/NO2 ratios between model and observations is achieved by including both a photolytic source of HONO at the ground and on the aerosol. Model sensitivity studies show that the observed diurnal variations of HONO/NO2 ratio are not reproduced by the model if there is only a photolytic HONO source on aerosol or in the gas-phase from NO2* + H2O. Further analysis of the formation and loss pathways of HONO shows a vertical dependence of HONO chemistry during the day. Photolytic HONO formation at the ground is the major formation pathway in the lowest 20 m, while a combination of gas-phase, photolytic formation on aerosol, and vertical transport is responsible for daytime HONO between 200–300 m a.g.l. HONO removal is dominated by vertical transport below 20 m and photolysis between 200–300 m a.g.l.

Air pollution and cloud-interaction over Europe in 1985 and today

2020 ◽  
Author(s):  
Roland Schrödner ◽  
Christa Genz ◽  
Bernd Heinold ◽  
Holger Baars ◽  
Silvia Henning ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Transport Model ◽  
Cloud Droplet ◽  
Forecast Model ◽  
Sensitivity Study ◽  
High Definition ◽  
Chemistry Transport Model ◽  
Meteorological Model ◽  
Cloud Properties ◽  
Aerosol Mass

&lt;p&gt;Aerosol concentrations over Europe and Germany were simulated for the years 1985 and 2013 using the aerosol-chemistry transport model COSMO-MUSCAT. The aerosol fields from the two simulations were used in a high-resolution meteorological model for a sensitivity study on cloud properties. The modelled aerosol and cloud variables were compared to a variety of available observations, including satellites, remote sensing and in-situ observations. Finally, the radiative forcing of the aerosol could be estimated from the different sensitivity simulations.&lt;/p&gt;&lt;p&gt;Due to reduction of emissions the ambient aerosol mass and number in Europe was strongly decreased since the 1980s. Hence, today&amp;#8217;s number of particles in the CCN size range is smaller. The HD(CP)&lt;sup&gt;2&lt;/sup&gt; (High Definition Clouds and Precipitation for Climate Prediction) project amongst others aimed at analysing the effect of the emission reduction on cloud properties.&lt;/p&gt;&lt;p&gt;As a pre-requiste, the aerosol mass, number, and composition over Germany were simulated for 1985 and 2013 using the regional chemistry-transport-model COSMO-MUSCAT. The EDGAR emission inventory was used for both years.&lt;/p&gt;&lt;p&gt;The model results were compared to observations from the two HD(CP)&lt;sup&gt;2&lt;/sup&gt; campaigns that took place in 2013 (HOPE, HOPE-Melpitz) as well as the AVHRR aerosol optical thickness product, which is available from 1981 onwards. Despite the fact, that emissions of the 1980s are very uncertain, the modelled AOD is in good agreement with observations. The modelled mean CCN number concentration in 1985 is a factor of 2-4 higher than in 2013.&lt;/p&gt;&lt;p&gt;Within HD(CP)&lt;sup&gt;2&lt;/sup&gt;, the ICON weather forecast model was applied in a configuration allowing for large-eddy simulations. In these simulations, the time-varying CCN fields for the year 1985 and 2013 calculated with COSMO-MUSCAT were used as input for ICON-LEM. In the present-day simulation, the cloud droplet number agrees with observations, whereas the perturbed (1985) simulation does not with droplet numbers about twice as high as in 2013. Also, for other cloud variables systematic changes between the two scenarios were observed.&lt;/p&gt;

scholarly journals The kinetics and mechanism of an aqueous phase isoprene reaction with hydroxyl radical

2011 ◽  
Vol 11 (15) ◽  
pp. 7399-7415 ◽  
Author(s):  
D. Huang ◽  
X. Zhang ◽  
Z. M. Chen ◽  
Y. Zhao ◽  
X. L. Shen
Keyword(s):  
Oxalic Acid ◽  
Gas Phase ◽  
Organic Compounds ◽  
Aqueous Phase ◽  
Laboratory Simulation ◽  
Potential Contribution ◽  
Phase Reaction ◽  
Oh Radical ◽  
Reaction Products ◽  
Isoprene Oxidation

Abstract. Aqueous phase chemical processes of organic compounds in the atmosphere have received increasing attention, partly due to their potential contribution to the formation of secondary organic aerosol (SOA). Here, we analyzed the aqueous OH-initiated oxidation of isoprene and its reaction products including carbonyl compounds and organic acids, regarding the acidity and temperature as in-cloudy conditions. We also performed a laboratory simulation to improve our understanding of the kinetics and mechanisms for the products of aqueous isoprene oxidation that are significant precursors of SOA; these included methacrolein (MACR), methyl vinyl ketone (MVK), methyl glyoxal (MG), and glyoxal (GL). We used a novel chemical titration method to monitor the concentration of isoprene in the aqueous phase. We used a box model to interpret the mechanistic differences between aqueous and gas phase OH radical-initiated isoprene oxidations. Our results were the first demonstration of the rate constant for the reaction between isoprene and OH radical in water, 1.2 ± 0.4) × 1010 M−1 s−1 at 283 K. Molar yields were determined based on consumed isoprene. Of note, the ratio of the yields of MVK (24.1 ± 0.8 %) to MACR (10.9 ± 1.1%) in the aqueous phase isoprene oxidation was approximately double that observed for the corresponding gas phase reaction. We hypothesized that this might be explained by a water-induced enhancement in the self-reaction of a hydroxy isoprene peroxyl radical (HOCH2C(CH3)(O2)CH = CH2) produced in the aqueous reaction. The observed yields for MG and GL were 11.4 ± 0.3 % and 3.8 ± 0.1 %, respectively. Model simulations indicated that several potential pathways may contribute to the formation of MG and GL. Finally, oxalic acid increased steadily throughout the course of the study, even after isoprene was consumed completely. The observed yield of oxalic acid was 26.2 ± 0.8 % at 6 h. The observed carbon balance accounted for ~50 % of the consumed isoprene. The presence of high-molecular-weight compounds may have accounted for a large portion of the missing carbons, but they were not quantified in this study. In summary, our work has provided experimental evidence that the availably abundant water could affect the distribution of oxygenated organic compounds produced in the oxidation of volatile organic compounds.

scholarly journals CAPRAM reduction towards an operational multiphase halogen and DMS chemistry treatment in the chemistry transport model COSMO-MUSCAT(5.04e)

2020 ◽  
Author(s):  
Erik H. Hoffmann ◽  
Roland Schrödner ◽  
Andreas Tilgner ◽  
Ralf Wolke ◽  
Hartmut Herrmann
Keyword(s):  
Gas Phase ◽  
Aqueous Phase ◽  
Transport Model ◽  
Chemical Transport ◽  
Regional Models ◽  
Gas Phase Reactions ◽  
Oxidation Rates ◽  
Reduced Mechanism ◽  
Equilibrium Reactions ◽  
Stratiform Clouds

Abstract. A condensed multiphase halogen and dimethyl sulfide (DMS) chemistry mechanism for application in chemical transport models is developed by reducing the CAPRAM DMS module 1.0 (CAPRAM-DM1.0) and the CAPRAM halogen module 3.0 (CAPRAM-HM3.0). The reduction is achieved by determining the main oxidation pathways from analysing the mass fluxes of complex multiphase chemistry simulations with the air parcel model SPACCIM. These simulations are designed to cover both pristine and polluted marine boundary layer conditions. Overall, the reduced DM1.0 contains 32 gas-phase reactions, 5 phase transfers, and 12 aqueous-phase reactions, of which two processes are described as equilibrium reactions. The reduced CAPRAM-HM3.0 contains 199 gas-phase reactions, 23 phase transfers, and 87 aqueous-phase reactions. For the aqueous-phase chemistry, 39 processes are described as chemical equilibrium reactions. A comparison of simulations using the complete DM1.0 and CAPRAM-HM3.0 mechanisms against the reduced ones indicates that the percentage deviations are below 5 % for important inorganic and organic air pollutants and key reactive species under pristine ocean and polluted conditions. The reduced mechanism has been implemented into the chemical transport model COSMO-MUSCAT and tested by performing 2D-simulations under prescribed meteorological conditions that investigate the effect of stable (stratiform cloud) and more unstable weather conditions (convective clouds) on marine multiphase chemistry. The simulated maximum concentrations of HCl are in the range of 109 molecules cm−3 and those of BrO are at around 1 · 107 molecules cm −3 reproducing the range of ambient measurements. Afterwards, the oxidation pathway of DMS in a cloudy marine atmosphere has been investigated in detail. The simulations demonstrate that clouds have both a direct and an indirect photochemical effect on the multiphase processing of DMS and its oxidation products. The direct photochemical effect is related to in-cloud chemistry that leads to high DMSO oxidation rates and a subsequently enhanced formation of methane sulfonic acid compared to aerosol chemistry. The indirect photochemical effect is characterised by cloud shading, which occurs particularly in the case of stratiform clouds. The lower photolysis rate affects the activation of Br atoms and consequently lowers the formation of BrO radicals. The corresponding DMS oxidation flux is lowered by up to 30 % under thick optical clouds. Moreover, high updraft velocities lead to a strong vertical mixing of DMS into the free troposphere predominately under cloudy conditions. Furthermore, HOX photolysis is reduced as well, resulting in higher HOX-driven sulfite oxidation in aerosol particles below stratiform clouds. Altogether, the present model simulations have demonstrated the ability of the reduced mechanism to be applied in studying marine aerosol cloud processing effects in regional models such as COSMO-MUSCAT and can be applied for more adequate interpretations of complex marine field measurement data, also by other regional models.

scholarly journals Formation mechanisms of atmospheric nitrate and sulfate during the winter haze pollution periods in Beijing: gas-phase, heterogeneous and aqueous-phase chemistry

2019 ◽  
Author(s):  
Pengfei Liu ◽  
Can Ye ◽  
Chaoyang Xue ◽  
Chenglong Zhang ◽  
Yujing Mu ◽  
...  
Keyword(s):  
Gas Phase ◽  
Aqueous Phase ◽  
Sampling Period ◽  
Convincing Evidence ◽  
Formation Mechanisms ◽  
Phase Reaction ◽  
So2 Oxidation ◽  
Mean Values ◽  
Sulfate Production ◽  
Haze Pollution

Abstract. A vast area in China is currently going through severe haze episodes with drastically elevated concentrations of PM2.5 in winter. Nitrate and sulfate are main constituents of PM2.5 but their formations via NO2 and SO2 oxidation are still not comprehensively understood, especially under different pollution or atmospheric relative humidity (RH) conditions. To elucidate formation pathways of nitrate and sulfate in different polluted cases, hourly samples of PM2.5 were collected continuously in Beijing during the wintertime of 2016. Three serious pollution cases were identified reasonably during the sampling period and the secondary formations of nitrate and sulfate were found to make a dominant contribution to atmospheric PM2.5 under the relatively high RH condition. The significant correlation between NOR and NO2 × O3 during the nighttime under the RH ≥ 60 % condition indicated that the heterogeneous hydrolysis of N2O5 involving aerosol liquid water was responsible for the nocturnal formation of nitrate at the extremely high RH levels. The more coincident trend of NOR and HONO × DR (direct radiation) × NO2 than Dust × NO2 during the daytime under the 30 % < RH < 60 % condition provided convincing evidence that the gas-phase reaction of NO2 with OH played a pivotal role in the diurnal formation of nitrate at moderate RH levels. The extremely high mean values of SOR during the whole day under the RH ≥ 60 % condition could be ascribed to the evident contribution of SO2 aqueous-phase oxidation to the formation of sulfate during the severe pollution episodes. Based on the parameters measured in this study and the known sulfate production rate calculation method, the oxidation pathway of H2O2 rather than NO2 was found to contribute greatly to the aqueous-phase formation of sulfate.

scholarly journals Modeling of daytime HONO vertical gradients during SHARP 2009

2013 ◽  
Vol 13 (7) ◽  
pp. 3587-3601 ◽  
Author(s):  
K. W. Wong ◽  
C. Tsai ◽  
B. Lefer ◽  
N. Grossberg ◽  
J. Stutz
Keyword(s):  
Boundary Layer ◽  
Gas Phase ◽  
Rural Areas ◽  
Transport Model ◽  
Vertical Transport ◽  
Formation Mechanisms ◽  
Aerosol Model ◽  
Formation Pathway ◽  
Sensitivity Studies ◽  
Urban And Rural Areas

Abstract. Nitrous acid (HONO) acts as a major precursor of the hydroxyl radical (OH) in the urban atmospheric boundary layer in the morning and throughout the day. Despite its importance, HONO formation mechanisms are not yet completely understood. It is generally accepted that conversion of NO2 on surfaces in the presence of water is responsible for the formation of HONO in the nocturnal boundary layer, although the type of surface on which the mechanism occurs is still under debate. Recent observations of higher than expected daytime HONO concentrations in both urban and rural areas indicate the presence of unknown daytime HONO source(s). Various formation pathways in the gas phase, and on aerosol and ground surfaces have been proposed to explain the presence of daytime HONO. However, it is unclear which mechanism dominates and, in the cases of heterogeneous mechanisms, on which surfaces they occur. Vertical concentration profiles of HONO and its precursors can help in identifying the dominant HONO formation pathways. In this study, daytime HONO and NO2 vertical profiles, measured in three different height intervals (20–70, 70–130, and 130–300 m) in Houston, TX, during the 2009 Study of Houston Atmospheric Radical Precursors (SHARP) are analyzed using a one-dimensional (1-D) chemistry and transport model. Model results with various HONO formation pathways suggested in the literature are compared to the the daytime HONO and HONO/NO2 ratios observed during SHARP. The best agreement of HONO and HONO/NO2 ratios between model and observations is achieved by including both a photolytic source of HONO at the ground and on the aerosol. Model sensitivity studies show that the observed diurnal variations of the HONO/NO2 ratio are not reproduced by the model if there is only a photolytic HONO source on aerosol or in the gas phase from NO2* + H2O. Further analysis of the formation and loss pathways of HONO shows a vertical dependence of HONO chemistry during the day. Photolytic HONO formation at the ground is the major formation pathway in the lowest 20 m, while a combination of gas-phase, photolytic formation on aerosol, and vertical transport is responsible for daytime HONO between 200–300 m a.g.l. HONO removal is dominated by vertical transport below 20 m and photolysis between 200–300 m a.g.l.

scholarly journals Contributions of anthropogenic and natural sources of sulfur to SO<sub>2</sub>, H<sub>2</sub>SO<sub>4</sub>(g) and nanoparticle formation

2007 ◽  
Vol 7 (3) ◽  
pp. 7679-7721 ◽  
Author(s):  
D. D. Lucas ◽  
H. Akimoto
Keyword(s):  
Gas Phase ◽  
Northern Hemisphere ◽  
Human Activities ◽  
Transport Model ◽  
Atmospheric Transport ◽  
Cloud Droplets ◽  
Model Calculations ◽  
Modern Times ◽  
Gas Phase Molecules ◽  
Anthropogenic Contribution

Abstract. Atmospheric nanoparticles (NPs) are important intermediates in the transition from gas-phase molecules to new aerosols that can activate into cloud droplets. Through increases in the emissions of sulfur-containing gases, human activities have likely increased the number of NPs produced in the atmosphere. To have significant impacts, however, sulfur pollution must be transported away from the surface, where NP formation is inefficient, to higher altitudes. To characterize this anthropogenic influence, tagged tracers are implemented in a global atmospheric transport model. The tagged tracers are used to track the contributions of sulfur from five sources (anthropogenic, oceanic, volcanic, aircraft, and stratospheric) to the gas-phase burdens of SO2 and H2SO4(g), and the rates of forming atmospheric NPs. Because NPs may be produced by a variety of mechanisms, three different aerosol nucleation schemes (binary, ternary and ion-induced) are used in the model calculations. Of the SO2 in the global troposphere, the tagged tracers indicate that about 69% originates from anthropogenic surface emissions, 20% from the oceans and 10% from de-gassing volcanoes. The same sources contribute about 56%, 24% and 19%, respectively, to the global tropospheric H2SO4(g) burden. The anthropogenic contribution for H2SO4(g) is reduced because anthropogenic SO2 produces H2SO4(g) less efficiently than oceanic and volcanic sulfur. Regardless of the underlying nucleation assumptions, the simulations show a pronounced influence of anthropogenic sulfur on atmospheric NP formation, particularly in the Northern Hemisphere. Utilizing the tagged H2SO4(g) contributions, anthropogenic sulfur is estimated to account for roughly 69% of the NP formation in the Northern Hemisphere, 31% in the Southern Hemisphere and 56% across the global troposphere. In the key region of the upper troposphere, anthropogenic and oceanic sulfur both make sizeable contributions to NP formation (54% and 37%, respectively). The tagged tracer contributions suggest that human activities have probably more than doubled the NP production rate in the atmosphere from preindustrial to modern times.

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