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Characteristics of Urban Ozone Formation During CAREBEIJING-2007 Experiment

Characteristics of Urban Ozone Formation During CAREBEIJING-2007 Experiment. Zhen Liu 04/21/09. Outline. 1. Introduction and methods. 2. Observed O 3 precursors and their implications . 3. PAN simulation with aromatics + OH  methylglyoxal. 4. Characteristics of ozone formation.

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Characteristics of Urban Ozone Formation During CAREBEIJING-2007 Experiment

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  1. Characteristics of Urban Ozone Formation During CAREBEIJING-2007 Experiment Zhen Liu 04/21/09

  2. Outline 1. Introduction and methods 2. Observed O3 precursors and their implications 3. PAN simulation with aromatics + OH methylglyoxal 4. Characteristics of ozone formation 5. Summary

  3. Campaigns of Air Quality Research in Beijing and surounding Region Adapted from Zhu’s Overview of CAREBEIJING study

  4. A 1-D photochemical model The 1-D photochemical model (e.g. Wang et al., 2008) driven by WRF assimilated meteorology fields adopts the photochemical and dry and wet deposition modules from the GEOS-CHEM model (Bey et al., 2001). The model includes a detailed photochemical mechanism with about 200 reactions and 120 concentration-varying chemical species; 24 tracers (family or species) are transported using the scheme by Walcek (2000) to describe O3-NOx–hydrocarbon chemistry. The in situ measurement data and 3D-REAM output were used to constrain the model. In situ observation and 3-D REAM output O3-NOx-hydrocarbon chemistry 200 reactions involving 120 species WRF Meteorology fields Transport 24 tracers, 35 vertical layers

  5. Average Daytime NOy Budget for 10 - 28 August 2007 Total NOy: 28.2ppbv N2O5 Residual 0.02% 12.2% NO HNO4 0.06% 17.3% HONO 3.8% PAN 13.6% NO2 29.6% HNO3 23.3% NO NO2 HNO3 PAN HONO HNO4 N2O5 Residual Observed O3 precursors – NOy species

  6. Average VOC composition Total VOC: 303.5 ppbC Alkanes 31% Aromatics 64% Alkenes 5% Alkanes Alkenes Aromatics Observed O3 precursors – VOC species Table 1. Comparison of the emission inventory based SSC and observed mixing ratios for aromatic species *steady state concentration

  7. PAN simulation with aromatics + OH methylglyoxal Table 2 Methylglyoxal yields and related reaction rate constants used in the photochemical model

  8. Ozone formation rate and HOx in different scenarios S1: neither PAN nor HONO is constrained S2: PAN constrained with observation S3: HONO constrained with observation S4: both PAN and HONO constrained with observation S5: S2+aromaticsMGLY S6: S4+aromaticsMGLY

  9. Ozone formation rate sensitivity to NOx levels – only standard scenario Typical VOC limited regime Daytime evolution

  10. Summary • A 1-D photochemical model was applied to analyze a full suite of atmospheric pollutants data during CAREBEIJING-2007 Experiment (August 2007). • Observed oxidants (PAN and HNO2) levels are much higher than predicted from the standard model, which almost increase by 100% the ozone formation rate, as well as the HOx (OH and HO2) concentration. • The abundance of aromatic VOC (~60% of total VOC in ppbC) leading to the high level of methylglyoxal appears to play a key role in PAN formation. • Tests for ozone sensitivity to NOx levels indicate the typical VOC-limited mechanism of ozone formation in urban Beijing.

  11. Thanks a lot!

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