scholarly journals Methyl hydroperoxide (CH<sub>3</sub>OOH) in urban, suburban and rural atmosphere: ambient concentration, budget, and contribution to the atmospheric oxidizing capacity

2012 ◽  
Vol 12 (5) ◽  
pp. 13089-13118 ◽  
Author(s):  
X. Zhang ◽  
S. Z. He ◽  
Z. M. Chen ◽  
Y. Zhao ◽  
W. Hua
Keyword(s):  
Free Radical ◽  
Diurnal Cycle ◽  
Marine Boundary Layer ◽  
Primary Sources ◽  
Mixing Ratios ◽  
Wide Range ◽  
Methyl Hydroperoxide ◽  
Measuring Site ◽  
Rural Sites ◽  
The Impact

Abstract. Methyl hydroperoxide (MHP), one of the most important organic peroxides in the atmosphere, contributes to the tropospheric oxidizing capacity either directly as an oxidant or indirectly as a free radical precursor. In this study we report measurements of MHP from seven field campaigns at urban, suburban and rural sites in China in winter 2007 and summer 2006/2007/2008. MHP was usually present in the order of several hundreds of pptv level, but the average mixing ratios have shown a wide range depending on the season and measuring site. Primary sources and sinks of MHP are investigated to understand the impact of meteorological and chemical parameters on the atmospheric MHP budget. The MHP/(MHP+H2O2) ratio is also presented here to examine different sensitivities of MHP and H2O2 to certain atmospheric processes. The diurnal cycle of MHP/(MHP+H2O2), which is out of phase with the diurnal cycle of both H2O2 and MHP, could imply that MHP production is more sensitive to the ambient NO concentration, while H2O2 is more strongly influenced by the wet deposition and the subsequent aqueous chemistry. It is interesting to note that our observation at urban Beijing site in winter 2007 provides evidence for the occasional transport of MHP-containing air masses from the marine boundary layer to the continent. Highly constrained box model is performed to study the influence of MHP on the free radical cycle. The simulation shows that MHP has a significant impact on the CH3O2 racial budget in the atmosphere. Furthermore, the contribution of MHP as an atmospheric oxidant to the overall tropospheric oxidizing capacity is also assessed based on the "Counter Species" concept.

scholarly journals Methyl hydroperoxide (CH<sub>3</sub>OOH) in urban, suburban and rural atmosphere: ambient concentration, budget, and contribution to the atmospheric oxidizing capacity

2012 ◽  
Vol 12 (19) ◽  
pp. 8951-8962 ◽  
Author(s):  
X. Zhang ◽  
S. Z. He ◽  
Z. M. Chen ◽  
Y. Zhao ◽  
W. Hua
Keyword(s):  
Marine Boundary Layer ◽  
Primary Sources ◽  
Air Masses ◽  
Sources And Sinks ◽  
Mixing Ratios ◽  
Wide Range ◽  
Methyl Hydroperoxide ◽  
Measuring Site ◽  
Rural Sites ◽  
The Impact

Abstract. Methyl hydroperoxide (MHP), one of the most important organic peroxides in the atmosphere, contributes to the tropospheric oxidizing capacity either directly as an oxidant or indirectly as a free radical precursor. In this study we report measurements of MHP from seven field campaigns at urban, suburban and rural sites in China in winter 2007 and summer 2006/2007/2008. MHP was usually present in the order of several hundreds of pptv level, but the average mixing ratios have shown a wide range depending on the season and measuring site. Primary sources and sinks of MHP are investigated to understand the impact of meteorological and chemical parameters on the atmospheric MHP budget. The MHP/(MHP+H2O2) ratio is also presented here to examine different sensitivities of MHP and H2O2 to certain atmospheric processes. The diurnal cycle of MHP/(MHP+H2O2), which is out of phase with that of both H2O2 and MHP, could imply that MHP production is more sensitive to the ambient NO concentration, while H2O2 is more strongly influenced by the wet deposition and the subsequent aqueous chemistry. It is interesting to note that our observation at urban Beijing site in winter 2007 provides evidence for the occasional transport of MHP-containing air masses from the marine boundary layer to the continent. Furthermore, the contribution of MHP as an atmospheric oxidant to the oxidizing capacity of an air parcel is assessed based on the "Counter Species" concept.

Contemporary Sri Lankan Buddhist Traditions

2016 ◽  
Author(s):  
Mahinda Deegalle
Keyword(s):  
Primary Sources ◽  
Sri Lankan ◽  
Social Changes ◽  
Human Flourishing ◽  
Cultural Elements ◽  
Buddhist Tradition ◽  
Wide Range ◽  
The Face ◽  
Historical Developments ◽  
The Impact

This chapter introduces the longest surviving living Buddhist tradition in the world. It outlines specific features of historical developments of the Sri Lankan Theravada Buddhist heritage. Dramatic historical and contemporary adaptations, made in response to the realities of political and social changes, are discussed by taking into account vernacular sources and archaeological research. A wide range of doctrinal and sociopolitical perspectives, along with Buddhist beliefs and practices, is examined by considering the incorporation of Hindu deities and Mahayana cultural elements. It notes European/Western encounters that produced radical developments in lifestyle and Buddhist ideology. The impact of civil war is briefly discussed, along with Marxist political groups such as the Janatha Vimukti Peramuna (JVP). Contemporary political and renewal movements within the tradition, such as the Jathika Hela Urumaya (JHU) and the Bodu Bala Sena, are investigated on the basis of primary sources. Challenges that living traditions face in the face of modernity, globalization, and secularism are examined by highlighting that Buddhism still inspires and guides for human flourishing.

scholarly journals NF-κB signaling pathway and free radical impact.

2012 ◽  
Vol 59 (3) ◽  
Author(s):  
Agnieszka Siomek
Keyword(s):  
Oxidative Stress ◽  
Transcription Factor ◽  
Free Radicals ◽  
Free Radical ◽  
Ionizing Radiation ◽  
Physiological Role ◽  
Growth And Survival ◽  
Wide Range ◽  
The Impact ◽  
And Oxidative Stress

The activation of NF-κB transcription factor is critical for a wide range of processes such as immunity, inflammation, cell development, growth and survival. It is activated by a variety of stimuli including cytokines, ionizing radiation and oxidative stress. Redox modulations of NF-κB pathway have been widely demonstrated. Studies carried out during last years have advanced our knowledge about possible connections between NF-κB pathway and the impact of free radicals. This review is an endeavor to gather recent results focused on this issue, although an important question, whether oxidative stress plays a physiological role in NF-κB activation, seems to be still unanswered.

scholarly journals Importance of reactive halogens in the tropical marine atmosphere: A regional modelling study using WRF-Chem

2017 ◽  
Author(s):  
Alba Badia ◽  
Claire E. Reeves ◽  
Alex R. Baker ◽  
Alfonso Saiz-Lopez ◽  
Rainer Volkamer ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Marine Boundary Layer ◽  
Transport Model ◽  
Model Performance ◽  
Sea Salt ◽  
Heterogeneous Reactions ◽  
Regional Modelling ◽  
Mixing Ratios ◽  
Inorganic Iodine ◽  
The Impact

Abstract. This study investigates the impact of halogens on atmospheric chemistry in the tropical troposphere and explores the sensitivity of this to uncertainties in the fluxes of halogens to the atmosphere and the chemical processing. To do this the regional chemistry transport model WRF-Chem has been extended, for the first time, to include halogen chemistry (bromine, chlorine and iodine chemistry), including heterogeneous recycling reactions involving sea-salt aerosol and other particles, reactions of Br with volatile organic compounds (VOCs), along with oceanic emissions of halocarbons, VOCs and inorganic iodine. The study focuses on the tropical East Pacific using field observations from the TORERO campaign (January–February 2012) to evaluate the model performance. Including all the new processes, the model does a reasonable job reproducing the observed mixing ratios of BrO and IO, albeit with some discrepancies, some of which can be attributed to difficulties in the model's ability to reproduce the observed halocarbons. This is somewhat expected given the large uncertainties in the air-sea fluxes of the halocarbons in a region where there are few observations of seawater concentrations. We see a considerable impact on the Bry partitioning when heterogeneous chemistry is included, with a greater proportion of the Bry in active forms such as BrO, HOBr and dihalogens. Including debromination of sea-salt increases BrO slightly throughout the free troposphere, but in the tropical marine boundary layer, where the sea-salt particles are plentiful and relatively acidic, debromination leads to overestimation of the observed BrO. However, it should be noted that the modelled BrO was extremely sensitive to the inclusion of reactions between Br and the VOCs, which convert Br to HBr, a far less reactive form of Bry. Excluding these reactions leads to modelled BrO mixing ratios greater than observed. The reactions between Br and aldehydes were found to be particularly important, despite the model underestimating the amount of aldehydes observed in the atmosphere. There are only small changes to Iy partitioning and IO when the heterogeneous reactions, primarly on sea-salt, are included. Our model results show that the tropospheric Ox loss due to halogens is 31 %. This loss is mostly due to I (16 %) and Br (14 %) and it is in good agreement with other estimates from state-of-the-art atmospheric chemistry models.

scholarly journals Global impact of nitrate photolysis in sea-salt aerosol on NO<sub><i>x</i></sub>, OH, and O<sub>3</sub> in the marine boundary layer

2018 ◽  
Vol 18 (15) ◽  
pp. 11185-11203 ◽  
Author(s):  
Prasad Kasibhatla ◽  
Tomás Sherwen ◽  
Mathew J. Evans ◽  
Lucy J. Carpenter ◽  
Chris Reed ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Field Studies ◽  
Sea Salt ◽  
Local Source ◽  
Global Impact ◽  
Mixing Ratios ◽  
Sea Salt Aerosol ◽  
The Impact

Abstract. Recent field studies have suggested that sea-salt particulate nitrate (NITs) photolysis may act as a significant local source of nitrogen oxides (NOx) over oceans. We present a study of the global impact of this process on oxidant concentrations in the marine boundary layer (MBL) using the GEOS-Chem model, after first updating the model to better simulate observed gas–particle phase partitioning of nitrate in the marine boundary layer. Model comparisons with long-term measurements of NOx from the Cape Verde Atmospheric Observatory (CVAO) in the eastern tropical North Atlantic provide support for an in situ source of NOx from NITs photolysis, with NITs photolysis coefficients about 25–50 times larger than corresponding HNO3 photolysis coefficients. Short-term measurements of nitrous acid (HONO) at this location show a clear daytime peak, with average peak mixing ratios ranging from 3 to 6 pptv. The model reproduces the general shape of the diurnal HONO profile only when NITs photolysis is included, but the magnitude of the daytime peak mixing ratio is under-predicted. This under-prediction is somewhat reduced if HONO yields from NITs photolysis are assumed to be close to unity. The combined NOx and HONO analysis suggests that the upper limit of the ratio of NITs : HNO3 photolysis coefficients is about 100. The largest simulated relative impact of NITs photolysis is in the tropical and subtropical marine boundary layer, with peak local enhancements ranging from factors of 5 to 20 for NOx, 1.2 to 1.6 for OH, and 1.1 to 1.3 for ozone. Since the spatial extent of the sea-salt aerosol (SSA) impact is limited, global impacts on NOx, ozone, and OH mass burdens are small ( ∼ 1–3 %). We also present preliminary analysis showing that particulate nitrate photolysis in accumulation-mode aerosols (predominantly over continental regions) could lead to ppbv-level increases in ozone in the continental boundary layer. Our results highlight the need for more comprehensive long-term measurements of NOx, and related species like HONO and sea-salt particulate nitrate, to better constrain the impact of particulate nitrate photolysis on marine boundary layer oxidant chemistry. Further field and laboratory studies on particulate nitrate photolysis in other aerosol types are also needed to better understand the impact of this process on continental boundary layer oxidant chemistry.

scholarly journals Transfer of organic Br and Cl from the Biosphere to the Atmosphere during the Cretaceous/Tertiary Impact: Implications for the stratospheric Ozone Layer

2004 ◽  
Vol 4 (5) ◽  
pp. 6769-6787 ◽  
Author(s):  
K. Kourtidis
Keyword(s):  
Biomass Burning ◽  
Stratospheric Ozone ◽  
Methyl Chloride ◽  
Ozone Layer ◽  
Emission Rates ◽  
Mixing Ratios ◽  
Wide Range ◽  
Order Of Magnitude ◽  
The Impact ◽  
Terrestrial Biomass

Abstract. Following the Cretaceous/Tertiary (K/T) meteoritic impact some 65 Myr ago, large portions of aboveground terrestrial biomass were burned. As a result, large amounts of various trace gases were injected to the atmosphere, inducing a wide range of effects on climate and ecosystems. Here, it is commented on the previously unaccounted emission to the atmosphere of methyl bromide (CH3Br) and methyl chloride (CH3Cl) from extensive biomass burning that followed the impact. Based on reported biomass burning emission rates of the above organohalogens relative to CO2, it is estimated that their emissions from global fires resulted in tropospheric mixing ratios of around 20–65.8 ppbv organic Cl and 110–390 pptv organic Br. The above calculated mixing ratios of active chlorine and bromine are more than an order of magnitude their present, anthropogenically perturbed level and, although the ocean ultimately might absorb them, we argue here that they could still remain in the stratosphere for many years, substantially affecting the ozone layer. This would have lead to very serious increases in short wavelength UV radiation reaching the lowermost atmosphere.

scholarly journals Global impact of nitrate photolysis in sea-salt aerosol on NO<sub>x</sub>, OH, and O<sub>3</sub> in the marine boundary layer

2018 ◽  
Author(s):  
Prasad Kasibhatla ◽  
Tomás Sherwen ◽  
Mathew J. Evans ◽  
Lucy J. Carpenter ◽  
Chris Reed ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Marine Boundary Layer ◽  
Field Studies ◽  
Sea Salt ◽  
Local Source ◽  
Global Impact ◽  
Mixing Ratios ◽  
Sea Salt Aerosol ◽  
The Impact

Abstract. Recent field studies have suggested that sea-salt particulate nitrate (NITs) photolysis may act as a significant local source of nitrogen oxides (NOx) over oceans. We present a study of the global impact of this process on oxidant concentrations in the marine boundary layer using the GEOS-Chem model, after first updating the model to better simulate observed gas/particle phase partitioning of nitrate in the marine boundary layer. Model comparisons with long-term measurements of NOx from the Cape Verde Atmospheric Observatory (CVAO) in the eastern tropical North Atlantic provide support for an in situ source of NOx from NITs photolysis, with NITs photolysis coefficients about 25–50 times larger than corresponding HNO3 photolysis coefficients. Short-term measurement of nitrous acid (HONO) at this location show a clear daytime peak, with average peak mixing ratios ranging from 3 to 6 pptv. The model reproduces the general shape of the diurnal HONO profile only when NITs photolysis is included, but the magnitude of the daytime peak mixing ratio is under-predicted. This under-prediction is somewhat reduced if HONO yields from NITs photolysis are assumed to be close to unity. The combined NOx and HONO analysis suggests that the upper limit of the ratio of NITs : HNO3 photolysis coefficients is about 100. The largest simulated relative impact of NITs photolysis is in the tropical and subtropical marine boundary layer, with peak local enhancements ranging from factors of 5–20 for NOx, 1.2–1.6 for OH, and 1.1–1.3 for ozone. Since the spatial extent of the sea-salt aerosol impact is limited, global impacts on NOx, ozone and OH mass burdens are small (~ 1–3 %). We also present preliminary analysis showing that particulate nitrate photolysis in accumulation-mode aerosols (predominantly over continental regions) could lead to ppbv-level increases in ozone in the continental boundary layer. Our results highlight the need for more comprehensive long-term measurements of NOx, and related species like HONO and sea-salt particulate nitrate, to better constrain the impact of particulate nitrate photolysis on marine boundary layer oxidant chemistry. Further field and laboratory studies on particulate nitrate photolysis in other aerosol types are also needed to better understand the impact of this process on continental boundary layer oxidant chemistry.

scholarly journals The impact of the chemical production of methyl nitrate from the NO + CH<sub>3</sub>O<sub>2</sub> reaction on the global distributions of alkyl nitrates, nitrogen oxides and tropospheric ozone: a global modelling study

2014 ◽  
Vol 14 (5) ◽  
pp. 2363-2382 ◽  
Author(s):  
J. E. Williams ◽  
G. Le Bras ◽  
A. Kukui ◽  
H. Ziereis ◽  
C. A. M. Brenninkmeijer
Keyword(s):  
Branching Ratio ◽  
Global Scale ◽  
Chemical Production ◽  
Alkyl Nitrates ◽  
Mixing Ratios ◽  
Wide Range ◽  
Oceanic Emissions ◽  
Methyl Nitrate ◽  
The Tropics ◽  
The Impact

Abstract. The formation, abundance and distribution of organic nitrates are relevant for determining the production efficiency and resident mixing ratios of tropospheric ozone (O3) on both regional and global scales. Here we investigate the effect of applying the recently measured direct chemical production of methyl nitrate (CH3ONO2) during NOx recycling involving the methyl-peroxy radical on the global tropospheric distribution of CH3ONO2 and the perturbations introduced towards tropospheric NOx and O3 using the TM5 global chemistry transport model. By comparisons against numerous observations, we show that the global surface distribution of CH3ONO2 can be largely explained by introducing the chemical production mechanism using a branching ratio of 0.3%, when assuming a direct oceanic emission source of ~0.15 Tg N yr−1. On a global scale, the chemical production of CH3ONO2 converts 1 Tg N yr−1 from nitrogen oxide for this branching ratio. The resident mixing ratios of CH3ONO2 are found to be highly sensitive to the dry deposition velocity that is prescribed, where more than 50% of the direct oceanic emission is lost near the source regions, thereby mitigating the subsequent effects due to long-range and convective transport out of the source region. For the higher alkyl nitrates (RONO2) we find improvements in the simulated distribution near the surface in the tropics (10° S–10° N) when introducing direct oceanic emissions equal to ~0.17 Tg N yr−1 . In terms of the vertical profile of CH3ONO2, there are persistent overestimations in the free troposphere and underestimations in the upper troposphere across a wide range of latitudes and longitudes when compared against data from measurement campaigns. This suggests either a missing transport pathway or source/sink term, although measurements show significant variability in resident mixing ratios at high altitudes at global scale. For the vertical profile of RONO2, TM5 performs better at tropical latitudes than at mid-latitudes, with similar features in the comparisons to those for CH3ONO2. Comparisons of CH3ONO2 with a wide range of surface measurements shows that further constraints are necessary regarding the variability in the deposition terms for different land surfaces in order to improve on the comparisons presented here. For total reactive nitrogen (NOy) ~20% originates from alkyl nitrates in the tropics and subtropics, where the introduction of both direct oceanic emissions and the chemical formation mechanism of CH3ONO2 only makes a ~5% contribution to the total alkyl nitrate content in the upper troposphere when compared with aircraft observations. We find that the increases in tropospheric O3 that occur due oxidation of CH3ONO2 originating from direct oceanic emission is negated when accounting for the chemical formation of CH3ONO2, meaning that the impact of such oceanic emissions on atmospheric lifetimes becomes marginal when a branching ratio of 0.3% is adopted.

scholarly journals Transfer of organic Br and Cl from the Biosphere to the Atmosphere during the Cretaceous/Tertiary Impact: Implications for the stratospheric Ozone Layer

2005 ◽  
Vol 5 (1) ◽  
pp. 207-214 ◽  
Author(s):  
K. Kourtidis
Keyword(s):  
Biomass Burning ◽  
Stratospheric Ozone ◽  
Methyl Chloride ◽  
Ozone Layer ◽  
Emission Rates ◽  
Mixing Ratios ◽  
Wide Range ◽  
Organic Chlorine ◽  
Order Of Magnitude ◽  
The Impact

Abstract. Following the Cretaceous/Tertiary (K/T) meteoritic impact some 65Myr ago, large portions of aboveground terrestrial biomass were burned. As a result, large amounts of various trace gases were injected to the atmosphere, inducing a wide range of effects on climate and ecosystems. Here, it is commented on the previously unaccounted for emission to the atmosphere of methyl bromide (CH3Br) and methyl chloride (CH3Cl) from extensive biomass burning that followed the impact. Based on reported biomass burning emission rates of the above organohalogens relative to CO2, it is estimated that their emissions from global fires resulted in tropospheric mixing ratios of around 20-65.8ppbv organic Cl and 110-390pptv organic Br. The above calculated mixing ratios of organic chlorine and bromine are more than an order of magnitude greater than their present, anthropogenically perturbed level and, although the ocean ultimately might absorb them, we argue here that they could still remain in the atmosphere for many years, and a substantial fraction could be transported to the stratosphere, thus substantially affecting the ozone layer. This would have led to very serious increases in short wavelength UV radiation reaching the lowermost atmosphere.

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