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Radical Precursors and Related Species from Traffic as Observed and Modeled

Radical Precursors and Related Species from Traffic as Observed and Modeled at an Urban Highway Junction. Bernhard Rappenglück 1 , Graciela Lubertino 2 , Sergio Alvarez 1 , Julia Golovko 1 , Beata Czader 1 , Luis Ackermann 1

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Radical Precursors and Related Species from Traffic as Observed and Modeled

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  1. Radical Precursors and Related Species from Traffic as Observed and Modeled at an Urban Highway Junction Bernhard Rappenglück1, Graciela Lubertino2, Sergio Alvarez1, Julia Golovko1, Beata Czader1, Luis Ackermann1 1) Department of Earth and Atmospheric Sciences, University of Houston2) Houston-Galveston Area Council, Houston

  2. Background • The Houston region is in non-attainment for: 1997 1-hr, and 2008 8-hr ozone standard • Study focus on ozone precursors: HONO, HCHO, CO, NO/NO2/NOx • Observational data is compared to modeling data (MOBILE6 and MOVES) at an urban highway junction in Houston

  3. RCH3 CO RCHO O3 PAN’s PAN PPN (anthropogenic) MPAN (biogenic) …. Daytime Gas-Phase Air Chemistry NOx-----VOC Photolysis of O3, RCHO, HONO, H2O2, ClNO2 + alkene ozonolysis Termination by NOx HNO3 Ozone (O3) H2O NO2 OH* CO2 + H2O ` H2O RCH* RC(O)O* +O2 O2 H* O(1D) RCH2O* +O2 RCO* O O +O2 +O2 NO +O2 RC(O)O2 * HO2* RCH2O2 * Termination by ROx + ROx H2O2 +HO2* +HO2* RCH2OOH

  4. RCH3 CO RCHO O3 PAN’s PAN PPN (anthropogenic) MPAN (biogenic) …. Daytime Gas-Phase Air Chemistry NOx-----VOC Photolysis of O3, RCHO, HONO, H2O2, ClNO2 + alkene ozonolysis Termination by NOx HNO3 Ozone (O3) H2O NO2 OH* CO2 + H2O ` H2O RCH* RC(O)O* +O2 O2 H* O(1D) RCH2O* +O2 RCO* O O +O2 +O2 NO +O2 RC(O)O2 * HO2* RCH2O2 * Termination by ROx + ROx H2O2 +HO2* +HO2* RCH2OOH

  5. Photolysis of O3, RCHO, HONO, H2O2, ClNO2 + alkene ozonolysis Termination by NOx HNO3 RCH3 H2O NO2 OH* CO CO2 + H2O RCHO O3 ` H2O RCH* RC(O)O* +O2 O2 H* O(1D) RCH2O* +O2 RCO* O O +O2 +O2 NO +O2 RC(O)O2 * PAN’s PAN PPN (anthropogenic) MPAN (biogenic) …. HO2* RCH2O2 * Termination by ROx + ROx H2O2 +HO2* +HO2* RCH2OOH Daytime Gas-Phase Air Chemistry NOx-----VOC minor ? mostly nighttime Ozone (O3) radical precursors Houston, TX Houston, TX Czader et al.,JGR, 2013 • Major HOx production mechanisms: • morning: HONO; mid morning: HCHO; throughout the day: O3

  6. Roadside Measurements Houston, TX

  7. Roadside Measurements Houston, TX Houston, Galleria

  8. TxDOT, 2009 Houston, TX (per day) Houston, Galleria

  9. Roadside Measurements Houston, Galleria Highway junction I-59 South/610 TxDOT pumping station

  10. Roadside Measurements Measurements (10 min) Houston, Galleria Highway junction I-59 South/610 TxDOT pumping station

  11. Average Diurnal Variation (Weekdays) Photochemical processes Elevated levels throughout the day due to ongoing traffic Morning rush hour

  12. Average Diurnal Variation (Weekdays) • Observational data screened for: • weekdays • Rush hour time 4-8 am CST • Global radiation < 10 W m-2 • PAN < 50 pptv • No precipitation • RH > 80% Morning rush hour

  13. Roadside Measurements Strong relationship of CO vs NOx (r2=0.91). Slope of 6.01 ppbv CO / 1 ppbv NOx is in agreement with Parrish et al. [2009] for rush hour times in selected cities.

  14. Emission Modeling

  15. Emission Modeling MOBILE6: hourly Harris county emission factors for on-road • Observed meteorology at the Galleria site for the model day: September 28, 2009 • 2009 local registration distribution • 2009 local diesel fractions • 2009 local VMT per hour • Local inspection and maintenance program • Anti-tampering program • Reformulated gasoline

  16. Emission Modeling MOVES: > MOVES2010a used to calculate EF for on-road and off network for NOx, CO, VOC, HCHO, CO2 (atm), NO, NO2. > MOVES2010b used to calculate HONO. • Avgspeeddistribution • Dayvmtfraction • Fuelformulation • Fuelengfraction • Fuelsupply • Hourvmtfraction • Hpmsvtypeyear • Imcoverage • Monthvmtfraction • Roadtypedistribution • Sourcetypeagedistribution • Sourcetypeyear • Zonemonthhour Using the Texas Transportation Institute suite of programs: • EFs adjusted for Tx Low Emission Diesel and the motorcycle rule • Emissions calculated multiplying the hourly adjusted emission factors (according to speed) by the hourly VMT per link, using the 2009 hourly VMT mix. • Output link-level emissions by vehicle type

  17. Emission Modeling Local 2009 diesel/gasoline split on the arterial and freeway facility types 6 am – 9 am CST 9 am – 3 pm CST 3 pm – 7 pm CST 7 pm – 6 am CST Something to consider: Total NOx emissions from Light Duty Gasoline (LDG) vehicles are about the same as from High Duty Diesel (HDD), although LDG vehicles are about 80% of the total registration, while HDD are about 7%....

  18. Diurnal variation of VMT for the Galleria site study area September 28, 2009

  19. Obs Results • Observations: 3.67±0.09 kg CO / kg NOx • Model results: For the morning rush hour, MOBILE6 overestimates the CO/NOx ratio by almost a factor of 2, while MOVES is 30% higher

  20. Obs Results • Observations: 3.14±0.14 g HCHO / kg CO • Model results: MOBILE6 largely underestimates Form/CO ratio MOVES calculates a very high ratio for very early morning due to heavy duty diesel off-road emissions (idling and starting trucks)

  21. Results • Model results: The differences in CO/NOx and HCHO/CO ratios are largely due to higher NOx and HCHO in MOVES (30% and 57% more than in MOBILE6), while CO emissions are about the same for both models.

  22. Obs Results • Observations: 0.017±0.0009 kg HONO / kg NOx • Model results: MOVES shows a constant HONO/NOx ratio based on a tunnel study done more than 15 years ago. The observed HONO/NOx ratio is twice the modeled.

  23. Obs Results • Observations: 0.0046±0.0002 kg HONO / kg CO • Model results: Due to the underestimation of HONO/NOx, MOVES also underestimates the HONO/CO ratio. Only at very early morning hours MOVES results are closer to the observations.

  24. Obs Results • Observations: 0.16±0.01 kg NO2 / kg NOx • Model results: Earlier studies showed a NO2/NOx ratio of 5%. MOVES shows a ratio of 9.3% for the rush hour time. The observation ratio is about twice.

  25. Obs Results • Observations: 0.0033±0.0002 kg CO / kg CO2 • Model results: MOVES calculates 3 times higher CO/CO2 than observed.

  26. Results • Observations: 0.0033±0.0002 kg CO / kg CO2 • Model results: MOVES calculates 3 times higher CO/CO2 than observed. It seems that MOVES overestimates the CO/CO2 from light duty gasoline vehicles

  27. Conclusions • CO/ NOx: • observations: 6.01±0.15 ppbv CO / 1 ppbv NOx (r2 = 0.91) in agreement with other studies. • MOBILE6 and MOVES, overestimate the corresponding observed emission ratio. MOVES gets closer, but 30% above the observed value. • HCHO/CO: • observations: 3.14±0.14 g HCHO / kg CO. • While MOBILE6 largely underestimates this ratio, MOVES calculates higher ratios, but is lower than the observed ratio. • MOVES shows high HCHO/CO ratios during the early morning hours due to heavy duty diesel off-road emissions (potential reasons are idling and starting trucks). • Differences of the modeled CO/NOx and HCHO/CO ratios: • largely due to higher NOx emissions in MOVES (30% increased from MOBILE6) and • higher HCHO emissions in MOVES (57% increased from MOBILE6); CO emissions about the same in both models.

  28. Conclusions • HONO/NOx: • observations: 0.017±0.0009 kg HONO / kg NOx which is twice as high as in MOVES. • NO2/NOx: • observations: 0.16±0.01 kg NO2 / kg NOx, which is ~70% higher than in MOVES. • CO/CO2: • observations: 0.0033±0.0002 kg CO / kg CO2 • MOVES overestimates by a factor of 3 compared with the observations. • Findings indicate: • overestimation of CO for light duty gasoline vehicles • underestimation of HONO and NO2 for heavy duty diesel vehicles in MOVES. Acknowledgements: • Houston Advanced Research Center (HARC) • TxDOT, Houston and Austin • TCEQ, Austin

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