scholarly journals Supplementary material to "Global inorganic nitrate production mechanisms: Comparison of a global model with nitrate isotope observations"

2019 ◽  
Author(s):  
Becky Alexander ◽  
Tomás Sherwen ◽  
Christopher D. Holmes ◽  
Jenny A. Fisher ◽  
Qianjie Chen ◽  
...  
Keyword(s):  
Global Model ◽  
Inorganic Nitrate ◽  
Nitrate Production ◽  
Supplementary Material ◽  
Production Mechanisms ◽  
Nitrate Isotope

scholarly journals Global inorganic nitrate production mechanisms: Comparison of a global model with nitrate isotope observations

2019 ◽  
Author(s):  
Becky Alexander ◽  
Tomás Sherwen ◽  
Christopher D. Holmes ◽  
Jenny A. Fisher ◽  
Qianjie Chen ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Reaction Rates ◽  
Oxygen Isotopic Composition ◽  
Heterogeneous Reactions ◽  
Relative Importance ◽  
Dinitrogen Pentoxide ◽  
Inorganic Nitrate ◽  
Nitrate Production ◽  
Oxygen Isotopic ◽  
Production Mechanisms

Abstract. The formation of inorganic nitrate is the main sink for nitrogen oxides (NOx = NO + NO2). Due to the importance of NOx for the formation of tropospheric oxidants such as the hydroxyl radical (OH) and ozone, understanding the mechanisms and rates of nitrate formation is paramount for our ability to predict the atmospheric lifetimes of most reduced trace gases in the atmosphere. The oxygen isotopic composition of nitrate (Δ17O(nitrate)) is determined by the relative importance of NOx sinks, and thus can provide an observational constraint for NOx chemistry. Until recently, the ability to utilize Δ17O(nitrate) observations for this purpose was hindered by our lack of knowledge about the oxygen isotopic composition of ozone (Δ17O(O3)). Recent and spatially widespread observations of Δ17O(O3) have greatly reduced this uncertainty, and allow for an updated comparison of modeled and observed Δ17O(nitrate) and a reassessment of modeled nitrate formation pathways. Model updates based on recent laboratory studies of heterogeneous reactions renders dinitrogen pentoxide (N2O5) hydrolysis as important as NO2 + OH (both 41 %) for global inorganic nitrate production near the surface. All other nitrate production mechanisms represent less than 6 % of global nitrate production near the surface, but can be dominant locally. Updated reaction rates for aerosol uptake of NO2 result in significant reduction of nitrate and nitrous acid (HONO) formed through this pathway in the model, and render NO2 hydrolysis a negligible pathway for nitrate formation globally. Although photolysis of aerosol nitrate may have implications for NOx, HONO and oxidant abundances, it does not significantly impact the relative importance of nitrate formation pathways. Modeled Δ17O(nitrate) (28.6 ± 4.5 ‰) compares well with the average of a global compilation of observations (27.6 ± 5.0 ‰), giving confidence in the model's representation of the relative importance of ozone versus HOx (= OH + HO2 + RO2) in NOx cycling and nitrate formation.

scholarly journals Global inorganic nitrate production mechanisms: comparison of a global model with nitrate isotope observations

2020 ◽  
Vol 20 (6) ◽  
pp. 3859-3877 ◽  
Author(s):  
Becky Alexander ◽  
Tomás Sherwen ◽  
Christopher D. Holmes ◽  
Jenny A. Fisher ◽  
Qianjie Chen ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Reaction Rates ◽  
Global Scale ◽  
Oxygen Isotopic Composition ◽  
Heterogeneous Reactions ◽  
Relative Importance ◽  
Inorganic Nitrate ◽  
Nitrate Production ◽  
Oxygen Isotopic ◽  
Production Mechanisms

Abstract. The formation of inorganic nitrate is the main sink for nitrogen oxides (NOx = NO + NO2). Due to the importance of NOx for the formation of tropospheric oxidants such as the hydroxyl radical (OH) and ozone, understanding the mechanisms and rates of nitrate formation is paramount for our ability to predict the atmospheric lifetimes of most reduced trace gases in the atmosphere. The oxygen isotopic composition of nitrate (Δ17O(nitrate)) is determined by the relative importance of NOx sinks and thus can provide an observational constraint for NOx chemistry. Until recently, the ability to utilize Δ17O(nitrate) observations for this purpose was hindered by our lack of knowledge about the oxygen isotopic composition of ozone (Δ17O(O3)). Recent and spatially widespread observations of Δ17O(O3) motivate an updated comparison of modeled and observed Δ17O(nitrate) and a reassessment of modeled nitrate formation pathways. Model updates based on recent laboratory studies of heterogeneous reactions render dinitrogen pentoxide (N2O5) hydrolysis as important as NO2 + OH (both 41 %) for global inorganic nitrate production near the surface (below 1 km altitude). All other nitrate production mechanisms individually represent less than 6 % of global nitrate production near the surface but can be dominant locally. Updated reaction rates for aerosol uptake of NO2 result in significant reduction of nitrate and nitrous acid (HONO) formed through this pathway in the model and render NO2 hydrolysis a negligible pathway for nitrate formation globally. Although photolysis of aerosol nitrate may have implications for NOx, HONO, and oxidant abundances, it does not significantly impact the relative importance of nitrate formation pathways. Modeled Δ17O(nitrate) (28.6±4.5 ‰) compares well with the average of a global compilation of observations (27.6±5.0 ‰) when assuming Δ17O(O3) = 26 ‰, giving confidence in the model's representation of the relative importance of ozone versus HOx (= OH + HO2 + RO2) in NOx cycling and nitrate formation on the global scale.

Supplementary material to "Manganese in the world ocean: a first global model"

2016 ◽  
Author(s):  
Marco van Hulten ◽  
Jean-Claude Dutay ◽  
Rob Middag ◽  
Hein de Baar ◽  
Matthieu Roy-Barman ◽  
...  
Keyword(s):  
World Ocean ◽  
Global Model ◽  
The World ◽  
Supplementary Material

scholarly journals Quantifying atmospheric nitrate formation pathways based on a global model of the oxygen isotopic composition (Δ<sup>17</sup>O) of atmospheric nitrate

2009 ◽  
Vol 9 (3) ◽  
pp. 11185-11220 ◽  
Author(s):  
B. Alexander ◽  
M. G. Hastings ◽  
D. J. Allman ◽  
J. Dachs ◽  
J. A. Thornton ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Global Scale ◽  
Oxygen Isotopic Composition ◽  
Global Model ◽  
Organic Nitrates ◽  
Polar Regions ◽  
Formation Pathway ◽  
Inorganic Nitrate ◽  
Atmospheric Nitrate ◽  
Oxygen Isotopic

Abstract. The oxygen isotopic composition (Δ17O) of atmospheric nitrate is a function of the relative abundance of atmospheric oxidants (O3, HOx=OH +HO2+RO2) and the formation pathway of nitrate from its precursor NOx (=NO+NO2). Coupled observations and modeling of nitrate Δ17O can be used to quantify the relative importance of chemical formation pathways leading to nitrate formation and reduce uncertainties in the budget of reactive nitrogen chemistry in the atmosphere. We present the first global model of atmospheric nitrate Δ17O and compare with available observations. The model shows the best agreement with a global compilation of observations when assuming a Δ17O value of tropospheric ozone equal to 35‰ and preferential oxidation of NOx by the terminal oxygen atoms of ozone. Calculated values of annual-mean nitrate Δ17O in the lowest model layer (0–200 m above the surface) vary from 6‰ in the tropics to 41‰ in the polar-regions. On the global scale, O3 is the dominant oxidant (81% annual-mean) during NOx cycling reactions. The global, annual-mean tropospheric inorganic nitrate burden is dominated by nitrate formation via NO2+OH (76%), followed by N2O5 hydrolysis (18%) and NO3+DMS/HC (4%). Model discrepancies are largest in the polar spring and summer, most likely due to the lack of reactive halogen chemistry in the model. The influence of organic nitrates on observations of nitrate Δ17O needs to be determined, especially for observations in summertime and tropical forested regions where organic nitrates can contribute up to 80% of the total NOy (organic plus inorganic nitrate) budget.

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