# Presentation: 673358

## A51B-0036  Uncertain Isoprene Emissions and Chemistry: Implications for Ozone in the Eastern United States

**A51B-0036  Uncertain Isoprene Emissions and Chemistry: Implications for Ozone in the Eastern United States**

**Arlene M. Fiore****1 ****(arlene.fiore@noaa.gov), Larry W. Horowitz****1****, George Milly****1****, Ronald C. Cohen****2****, Melody A. Avery****3****, Donald R. Blake****4****, Louisa K. Emmons****5****, Alan Fried****6****, Peter Hess****5****, **
**Jean-François Lamarque****5****, Anne Perring****2****, Gabriele G. Pfister****5****, Hanwant B. Singh****7****, James Walega****6****, Paul J. Wooldridge****2**
** ****1****NOAA/GFDL, Princeton, NJ  ****2****Department of Chemistry, UC Berkeley, Berkeley, CA  ****3****NASA Langley Research Center, Hampton, VA  ****4****UC Irvine, Irvine, CA  ****5****Atmospheric Chemistry Division, NCAR, Boulder, CO ****6****Earth Observing Laboratory, NCAR, Boulder, CO, ****7****NASA Ames Research Center, Moffett Field, CA**

**6. Conclusions**

**   ****Base Case MOZART-4 Simulation**
-  ~100 gas and aerosol species, ~200 reactions
-  NCEP Global Forecast System (GFS)
-  1.9o latitude x1.9o longitude x 64 vertical levels
-  Emissions: ICARTT anthropogenic and *Turquety et al*. [2005] daily biomass burning
-   from MODIS and NIFC (North America), POET 1997 (elsewhere) [*Olivier et al*., 2003]
-  MEGAN (v.0) isoprene emissions [*Guenther et al*., 2005]

** ****1. Introduction: Uncertain Isoprene Emissions and Chemistry**

**REFERENCES****	**
- Chen *et al*. (1998), *J. Geophys. Res., 103 (D19*), 25,563-25,568.
- Guenther *et al*. (1995), *J. Geophys. Res., 100*, 8873-8892.
- Guenther *et al.* (2005), *Atmos. Chem. Phys*., in preparation.
- Horowitz *et al*. (1998), *J. Geophys. Res., 103*, 13,451-13,476.

**OBJECTIVES**
** ****Explore chemical uncertainty associated with isoprene emissions and chemistry**
** ****Attempt to constrain uncertainties using ICARTT measurements **
** ****Quantify NO****x**** sink via isoprene nitrates**

**MEGAN isoprene emissions are consistent with observed isoprene and oxidation products; O****3**** increases in the northeast (up to 9 ppbv) and decreases in the southeast (up to 8 ppbv) compared to GEIA**
**Simulated ********ANs-O****3**** correlations approach the observed relationship for an isoprene nitrate burden of 1.1-1.5 Gg N (EUS below 2 km). This burden is obtained with either high yields and fast loss or small yields and slow loss**
**Model underestimates observed ********ANs in free troposphere by a factor of ~10, possibly due to assumed loss of multifunctional organic nitrates**
**~45% (36-56%) of isoprene nitrate production in the model occurs through highly uncertain NO****3**** chemistry**
** **
**~7-16% of NO****x**** emitted in the eastern U.S. is lost through isoprene nitrates and an additional 4-9% cycles through isoprene nitrates**
**We are grateful to Frank Flocke and Aaron Swanson (PAN), Joost de Gouw and Carsten Warneke (isoprene, MVK+MACR), and Tom Ryerson (O****3****), for providing their measurements aboard the NOAA WP-3B, and to Rynda Hudman for a one-minute merge of the P3 data.**

**Uncertainties in NO****x****-isoprene-O****3**** chemistry considered here: **

**Eastern U.S. emission estimates vary by more than a factor of 2: **

**MEGAN**
**  ****3.6 Tg**

**GEIA**
**3.9 Tg**

**Purves **
**1.9 Tg**

**July Isoprene Emissions (10****10**** kg m****-2**** s****-1****)**

**2. Apply MOZART-4 CTM to the ICARTT period (July-August 2004)**

**Sources of Uncertainty:**
** ****Base emission capacities and leaf area index ****[*****Guenther et al*****., 1995, *****Purves et al*****., 2004]**
** ****4 to 13% range on lab measurements of isoprene nitrate yields from isoprene + OH **
**  ****reaction [*****Tuazon and Atkinson*****, 1990; *****Chen et al*****., 1998, *****Sprengnether et al*****., 2002]**
** ****Importance of isoprene nitrates as a NO****x**** sink ****[*****Chen et al*****., 1998, *****Liang et al*****., 1998,**
**   *****Horowitz et al*****., 1998]**
** ****Fate of multifunctional organic nitrates; rapid deposition assumed in this study**

**4. Constraints from Observations**

** ****3. Isoprene Nitrate Budgets (July, Eastern U.S. below 2 km)**

**Ranges in model bias due to uncertain ****emissions**** and ****chemistry **
**(Eastern U.S. land boxes below 2 km, 10 a.m.–6 p.m. local time) **

- Statistics based on values averaged to model grid for each flight

- Use ICARTT measurements of total alkyl nitrates (ANs) and several individual alkyl nitrates to constrain uncertainties discussed in Section 1.

**NASA DC-8 Flights **

**Due to Emissions**

**Due to Chemistry**

**5. Impacts on Surface Ozone: ****Change in July mean afternoon (1-5 p.m. local time) surface O****3**

**   ****Maximum O****3**** decrease with a 12%    **
**   ****isoprene nitrate yield and slow loss**
**  ******** ****NO****x ****sink via isoprene nitrates  **
**       ****increases from 13% (Base) to**
**       ****16% (12%OHs) and  surface O****3 **
**          ****decreases by 2-5 ppbv **

- Model is sampled along flight tracks at 1-minute intervals

**Model can capture observed O****3****-********ANs relationship with:**
**           ******** ****high RONO****2**** yields (12%) with fast loss  **
**           ******** ****moderate yields and loss**
**           ******** ****small yields (4%) and slow loss **
**Best guess simulations highlighted in white (Section 3)**

**Higher southeastern emissions increase O****3**

| Simulation Name | Selected Loss Pathways |  |  | Yield from RO2+NO
(Production) |  |  | Lifetime
(hours) |
| --- | --- | --- | --- | --- | --- | --- | --- |
|  | OH | WET DEP | DRY DEP | 4% | 8% | 12% |  |
|  |  |  |  | Burden (Gg N) |  |  |  |
| BASE | FAST | FAST | FAST | -- | 0.6 | 0.7 | 4.1-4.3 |
| OHm | MEDIUM | FAST | FAST | -- | 1.0 | 1.1 | 7.2-7.3 |
| OHmWDs | MEDIUM | SLOW | FAST | -- | 1.0 | -- | 7.4 |
| OHmDDs | MEDIUM | FAST | SLOW | -- | 1.4 | -- | 10.1 |
| OHs | SLOW | FAST | FAST | 1.2 | 1.5 | 1.8 | 11.0-11.4 |
| OHsWDs | SLOW | SLOW | FAST | 1.2 | -- | -- | 11.5 |

**Simulations falling within observational constraints **
**(Section 4) are highlighted in white in the Table**

**NOAA WP-3D Flights **

**O****3**** **

**Isoprene**

**products**

**O****3**

- k298=1.3x10-17

**NO****3**** **

**Isoprene**

**R’O****2 **

**NO, NO****3****, HO****2**** **

**(80% RONO****2**** yield **
**assumed; balance **
**recycled to NO****2****)**

- k298=6.8x10-13

**8%BASE**
**8%OHm**
**12%OHm**
**4%OHs**
**8%OHmDD**
**8%OHs**

**Model underestimates free tropospheric ********ANs in all cases.**
**Due to assumed loss of **
**multifunctional organic nitrates? **

**Mean ICARTT vertical profiles of ********ANs**

- Each point is the mean
- value within one model
- grid box for one flight

******ANs – Ozone Correlations **
**(Eastern U.S. land boxes below 2 km, 10 a.m.–6 p.m. local time )**

**OZONE (ppbv)**

******ANs (pptv)**

- Note: PAN bias always <15% in free troposphere

**Purves - MEGAN**

**GEIA- MEGAN**

**Largest O****3**** decreases coincide with high **
**NO****x**** emissions**

**Production of Isoprene Nitrates (Gg N)**

**Loss of Isoprene Nitrates (Gg N)**

**36-56% of RONO****2**** forms**
**via NO****3**** pathway; needs further investigation**

**8%BASE- 12%OHs**

******ANs (pptv)**

**Altitude (km)**

***Shepson et al*****. [1996]**
**used loss rates similar**
**to simulation OHmDDs**

**RONO****2 ****(isoprene nitrates)**

**Deposition**

**O****3**

**OH **

**RO****2 **

**NO**** **

**Isoprene**

**NO****2**

**Yield**

**NO****x ****recycled**

- k298=1.0x10-10

**Other organic **
**nitrates**

**Lower northeastern isoprene emissions reduce O****3**** (up to 9 ppbv)**

- Liang *et al*. (1998), *J. Geophys. Res., 103*, 13,435-13,450.
- Olivier *et al*., (2003), POET Report #2, EU project EVK2-1999-00011.
- Purves *et al*. (2004), *Global Change Biology*, *10*, 1-19.
- Shepson *et al*. (1996), *Environ. Sci. Technol., 30*, 3618-3623.

- Sprengnether *et al.* (2002), *J. Geophys. Res., 107* *(D15),* 4269, doi:10.1029/2001JD000716.
- Tuazon, E.C., and R.E. Atkinson (1990), *Int. J. Chem. Kinet., 22*, 1221-1236.
- Turquety *et al*. (2005), *J. Geophys. Res*.,  in preparation.