Dusanter S

Publications (6)0 Total impact

• Source

  Available from: atmos-chem-phys-discuss.net

  Article: Impacts of HONO sources on the photochemistry in Mexico City during the MCMA-2006/MILAGO Campaign

  Li G, Lei W, Zavala M, Volkamer R, Dusanter S, Stevens P, L. T. Molina
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  ABSTRACT: The contribution of HONO sources to the photochemistry in Mexico City is investigated during the MCMA-2006/MILAGO Campaign using the WRF-CHEM model. Besides the homogeneous reaction of NO with OH, four additional HONO sources are considered in the WRF-CHEM model: secondary HONO formation from NO2 heterogeneous reaction with semivolatile organics, NO2 reaction with freshly emitted soot, NO2 heterogeneous reaction on aerosol and ground surfaces. The WRF-CHEM model with the five HONO sources performs reasonably well in tracking the observed diurnal variation of HONO concentrations. The HONO sources included are found to significantly improve the HOx (OH+HO2) simulations during daytime and the partition of NO/NO2 in the morning. The HONO sources also accelerate the accumulation of O3 concentrations in the morning by about 2 h and subsequently result in a noticeable enhancement of O3 concentrations over the course of the day with a midday average of about 6 ppb. Furthermore, these HONO sources play a very important role in the formation of secondary aerosols in the morning. They substantially enhance the secondary organic aerosol concentrations by a factor of 2 on average in the morning, although contribute less during the rest of the day. The simulated nitrate and ammonium aerosols are also remarkably enhanced in the morning when the four HONO sources are added, in good agreement with the measurements. The impact of the HONO sources on the sulfate aerosols is negligible because of the inefficient conversion of H2SO4 from SO2 reacting with OH.
  Atmospheric Chemistry and Physics Discussions. 01/2010;
• Source

  Available from: Simone Meinardi

  Article: Measurements of OH and HO₂ concentrations during the MCMA-2006 field campaign – Part 2: Model comparison and radical budget

  Dusanter S, Vimal D, P. S. Stevens, Volkamer R, L. T. Molina, Baker A, Meinardi S, D R Blake, Sheehy P, Merten A, Zhang R, Zheng J, E. C. Fortner, Junkermann W, M. K. Dubey, Rahn T, W. E. Eichinger, Lewandowski P, Prueger J, Holder H
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  ABSTRACT: Measurements of hydroxyl (OH) and hydroperoxy (HO₂) radicals were made during the Mexico City Metropolitan Area (MCMA) field campaign as part of the MILAGRO (Megacity Initiative: Local and Global Research Observations) project during March 2006. These measurements provide a unique opportunity to test current models of atmospheric RO_x (OH+HO₂+RO₂) photochemistry under polluted conditions. A zero-dimensional box model based on the Regional Atmospheric Chemical Mechanism (RACM) was constrained by 10-min averages of 24 J -values and the concentrations of 97 chemical species. Several issues related to the RO_x chemistry under polluted conditions are highlighted in this study: (i) median concentrations of both OH and HO₂ were underpredicted during morning hours, suggesting a significant source of radicals is missing from current atmospheric models under polluted conditions, consistent with previous urban field campaigns. (ii) The predicted HO₂/OH ratios were underestimated for NO mixing ratios higher than 5 ppb, also consistent with previous urban field campaigns. This suggests that under high NO_x conditions, the HO₂ to OH propagation rate may be overestimated by the model or a process converting OH into HO₂ may be missing from the chemical mechanism. On a daily basis (08:40 a.m.–06:40 p.m.), an analysis of the radical budget indicates that HONO photolysis, HCHO photolysis, O₃-alkene reactions and dicarbonyls photolysis are the main radical sources. O₃ photolysis contributes to less than 6% of the total radical production.
  Atmospheric Chemistry and Physics Discussions. 01/2009;
• Article: Measurements of OH and HO₂ concentrations during the MCMA-2006 field campaign – Part 2: Model comparison and radical budget

  Dusanter S, Vimal D, P. S. Stevens, Volkamer R, L. T. Molina, Baker A, Meinardi S, Blake D, Sheehy P, Merten A, Zhang R, Zheng J, E. C. Fortner, Junkermann W, Dubey M, Rahn T, Eichinger B, Lewandowski P, Prueger J, Holder H
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  ABSTRACT: Measurements of hydroxyl (OH) and hydroperoxy (HO₂) radicals were made during the Mexico City Metropolitan Area (MCMA) field campaign as part of the MILAGRO (Megacity Initiative: Local and Global Research Observations) project during March 2006. These measurements provide a unique opportunity to test current models of atmospheric RO_x (OH + HO₂ + RO₂) photochemistry under polluted conditions. A zero-dimensional box model based on the Regional Atmospheric Chemical Mechanism (RACM) was constrained by 10-min averages of 24 J -values and the concentrations of 97 chemical species. Several issues related to the RO_x chemistry under polluted conditions are highlighted in this study: (i) Measured concentrations of both OH and HO₂ were underpredicted during morning hours on a median campaign basis, suggesting a significant source of radicals is missing from current atmospheric models under polluted conditions, consistent with previous urban field campaigns. (ii) The model-predicted HO₂/OH ratios underestimate the measurements for NO mixing ratios higher than 5 ppb, also consistent with previous urban field campaigns. This suggests that under high NO_x conditions, the HO₂ to OH propagation rate may be overestimated by the model or a process converting OH into HO₂ may be missing from the chemical mechanism. On a daily basis (08:40 a.m.–06:40 p.m.), an analysis of the radical budget indicates that HONO photolysis, HCHO photolysis, O₃-alkene reactions and dicarbonyls photolysis are the main radical sources. O₃ photolysis contributes to less than 6% of the total radical production.
  Atmospheric Chemistry and Physics. 01/2009;
• Article: Technical note: Measuring tropospheric OH and HO2 by laser-induced fluorescence at low pressure. A comparison of calibration techniques

  Dusanter S, Vimal D, P. S. Stevens
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  ABSTRACT: The hydroxyl radical (OH) is one of the most important oxidants in the atmosphere, as it is involved in many reactions that affect regional air quality and global climate change. Because of its high reactivity, measurements of OH radical concentrations in the atmosphere are difficult, and often require careful calibrations that rely on the production of a known concentration of OH at atmospheric pressure. The Indiana University OH instrument, based on the Fluorescence Assay by Gas Expansion technique (FAGE), has been calibrated in the laboratory using two different approaches: the production of OH from the UV-photolysis of water-vapor, and the steady-state production of OH from the reaction of ozone with alkenes. The former technique relies on two different actinometric methods to measure the product of the lamp flux at 184.9 nm and the photolysis time. This quantity derived from N₂O actinometry was found to be 1.5 times higher than that derived from O₂ actinometry. The water photolysis and ozone-alkene techniques are shown to agree within their experimental uncertainties (respectively 17% and 44%), although the sensitivities derived from the ozone-alkene technique were systematically lower by 40% than those derived from the water-vapor UV- photolysis technique using O₂ actinometry. The agreement between the two different methods improves the confidence of the water-vapor photolysis method as an accurate calibration technique for HO_x instruments. Because several aspects of the mechanism of the gas phase ozonolysis of alkenes are still uncertain, this technique should be used with caution to calibrate OH instruments.
  Atmospheric Chemistry and Physics. 01/2008;
• Source

  Available from: Josef Dommen

  Article: Measurements of HNO₃ and N₂O₅ using ion drift-chemical ionization mass spectrometry during the MILAGRO/MCMA-2006 campaign

  Zheng J, Zhang R, E. C. Fortner, R. M. Volkamer, Molina L, A. C. Aiken, J. L. Jimenez, Gaeggeler K, Dommen J, Dusanter S, P. S. Stevens, Tie X
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  ABSTRACT: An ion drift-chemical ionization mass spectrometer (ID-CIMS) was deployed in Mexico City between 7 and 31 March to measure gas-phase nitric acid (HNO₃) and dinitrogen pentoxide (N₂O₅ during the Mexico City Metropolitan Area (MCMA)-2006 field campaign. The observation site was located at the Instituto Mexicano del Petróleo in the northern part of Mexico City urban area with major emissions of pollutants from residential, vehicular and industrial sources. Diurnally, HNO₃ was less than 200 parts per trillion (ppt) during the night and early morning. The concentration of HNO₃ increased steadily from around 09:00 a.m. central standard time (CST), reached a peak value of 0.5 to 3 parts per billion (ppb) in the early afternoon, and then declined sharply to less than half of the peak value near 05:00 p.m. CST. An inter-comparison between the ID-CIMS and an ion chromatograph/mass spectrometer (ICMS) showed a good agreement between the two HNO₃ measurements ( R ²=0.75). The HNO₃ mixing ratio was found to anti-correlate with submicron-sized aerosol nitrate, suggesting that the gas-particle partitioning process was a major factor in determining the gaseous HNO₃ concentration. Losses by irreversible reactions with mineral dust and via dry deposition also could be important at this site. Most of the times during the MCMA 2006 field campaign, N₂O₅ was found to be below the detection limit (about 30 ppt for a 10 s integration time) of the ID-CIMS, because of high NO mixing ratio at the surface (>100 ppb) during the night. An exception occurred on 26 March 2006, when about 40 ppt N₂O₅ was observed during the late afternoon and early evening hours under cloudy conditions before the build-up of NO at the surface site. The results revealed that during the MCMA-2006 field campaign HNO₃ was primarily produced from the reaction of OH with NO₂ and regulated by gas/particle transfer and dry deposition. The production of HNO₃ from N₂O₅ hydrolysis during the nighttime was small because of high NO and low O₃ concentrations near the surface.
  Atmospheric Chemistry and Physics. 01/2008;
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  Available from: atmos-chem-phys-discuss.net

  Article: Measurements of OH and HO₂ concentrations during the MCMA-2006 field campaign – Part 1: Deployment of the Indiana University laser-induced fluorescence instrument

  Dusanter S, Vimal D, P. S. Stevens, Volkamer R, L. T. Molina
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  ABSTRACT: Measurements of tropospheric hydroxyl (OH) and hydroperoxy (HO₂) radicals were made during the MCMA (Mexico City Metropolitan Area) field campaign as part of the MILAGRO (Megacity Initiative: Local and Global Research Observations) project during March 2006. These radicals were measured using a laser-induced fluorescence instrument developed at Indiana University. This new instrument takes advantage of the Fluorescence Assay by Gas Expansion technique (FAGE) together with direct excitation and detection of OH at 308 nm. HO₂ is indirectly measured as OH by titration with NO inside the fluorescence cell. At this stage of development, IU-FAGE is capable of detecting 3.9×10⁵molec cm⁻³ of both OH and HO₂, with a signal to noise ratio of 1, an averaged laser power of 10 mW and an averaging time of 5 min. The calibration accuracies (1σ) are ±17% for OH and ±18% for HO₂ using the water-vapor photolysis/O₂ actinometry calibration technique. OH and HO₂ concentrations were successfully measured at an urban site in Mexico City, with observed concentrations comparable to those measured in other polluted environments. Enhanced levels of OH and HO₂ radicals were observed on several days between 09:30–11 a.m. and suggest an intense photochemistry during morning hours that may be due to elevated sources of HO_x (OH+HO₂) and a fast cycling between the radicals under the high NO_x conditions of the MCMA. A comparison with other urban and sub-urban field measurements suggests that OH concentrations are highly buffered under these conditions. In contrast, HO₂ concentrations are highly variable between different urban sites.
  Atmospheric Chemistry and Physics Discussions. 01/2008;