1. Impact of lightning-NO emissions on eastern United States photochemistry during the summer of 2004 as determined using the CMAQ model
Dale Allen – University of Maryland, College Park, MD
Ken Pickering – NASA GSFC, Greenbelt, MD
Rob Pinder – US EPA, RTP, NC
Tom Pierce – US EPA, RTP, NC
2009 CMAS Meeting
October 19-21, 2009

2. Motivation for Including Lightning NOx in CMAQ
In the summer over the US, production of NO by lightning (LNOx) is responsible for 60-80% of upper tropospheric (UT) NOx and 20-30% of UT ozone.
Mid- and upper-tropospheric ozone production rates are highly sensitive to NOx mixing ratios.
Inversion-based estimates of NO emissions from CMAQ simulations without lightning-NO emissions have large errors at rural locations.
CMAQ-calculated nitrogen deposition is much too low when lightning-NO emissions are not included (e.g., Low-bias in CMAQ-calc nitric acid wet dep at NADP sites cut in half when lightning-NO was added).
Lightning-NO emissions can add several ppbv on average to summertime surface ozone concentrations

3. Outline
Describe method used to parameterize lightning-NO emissions within CMAQ.
Use CMAQ with and without lightning-NO emissions to simulate the tropospheric distribution of atmospheric trace gases over the US during the summer of 2004
Compare CMAQ-calculated trace gas distributions with
NOx and ozone measurements from INTEX-A field campaign
tropospheric NO2 columns from SCIAMACHY
Estimate the contribution of lightning-NO emissions to 8-hour maximum ozone

4. CMAQ setup
Continental US 36-km domain with 24 vertical layers from the surface to 100 hPa.
Meteorological fields from MM5
Emissions from SMOKE processing of 2002 NEI for use with CB-05 chemical mechanism
Year-appropriate point source emissions from CEMS
Mobile emissions processed by Mobile6
Meteorologically adjusted biogenic emissions from BEIS 3.13

5. CMAQ Lightning-NO emission Parameterization
LNOx = k* PROD*LF, where
k: Conversion factor (Molecular weight of N / Avogadros #)
PROD: Moles of NO produced per flash
LF: Total flash rate (IC + CG), where
LF = G * αi,j * (preconi,j – threshold), where
Precon: Convective precipitation rate from MM5
threshold: Value of precon below which the flash rate is set to zero.
G: Scaling factor chosen so that domain-avg MM5 flash rate matches domain averaged observed flash rate.
αi,j: Local scaling factor chosen so that monthly avg model- calc flash rate for each grid box equals local observed flash rate
For these retrospective simulations, the observed flash rate is the NLDN-based total flash rate for June, July, and August 2004.
Operational forecasts could use satellite-retrieved or NLDN-based climatological flash rates for a season as observations.

6. What is the NLDN-based total flash rate?
Hourly cloud-to-ground flash rates (CG) from the National Lightning Detection Network (US only) are mapped onto the CMAQ grid.
Hourly total flash rates (CG +IC) are estimated by multiplying the CG flash rate by (Z+1), where Z is the climatological IC/CG ratio Boccippio et al. [2001] determined by comparing satellite-retrieved (Optical Transient Detector instrument) total flash rates with NLDN CG flash rates.
Cautionary note:
Errors in NLDN-based total flash rate can be substantial as 1) IC flashes > CG flashes , 2) data set, 3) OTD only samples a few percent of total flashes

7. Boccippio et al., 2001
Mean IC/CG ~3. Adds uncertainty to NLDN-based total flash rate

8. Impact of local scaling on CMAQ-calculated flash rate
Based
CG+IC
(without α)
NLDN
Based
CG+IC
flash
rate
Local scaling compensates
for regional biases in
convective precipitation and
for continental-marine
differences in the relationship
between flash rate and precip
CMAQ
Based
CG+IC
(With α)

9. Day-to-day and diel fluctuations in flash rate over the
Eastern US (110°-70°W, 25°-45° N)
August 1 to August 31, 2004

10. Diel variations in flash rate (110°-70°W, 25°-45° N)
are well simulated
Universal Time

11. Day-to-day fluctuations in flash rate
(110°-70°W, 25°-45° N) well captured
August 1 to August 31, 2004

23. LNOx Production Per Flash
Globally, lightning produces 2-8 Tg N / year with a 5 Tg N / year source corresponding to a mean source of ~250 moles of N / flash.
However, recent cloud resolved chemistry modeling (DeCaria et al., 2000; 2005; Ott et al., 2005; 2007) of observed convective events (STERAO, EULINOX, CRYSTAL-FACE) and recent modeling of the INTEX-A period using GEOS-Chem, FLEXPART, REAM and other models [Singh et al., 2007] indicates that midlatitude and subtropical lightning has a mean source of ~500 moles of N / Flash.
In these simulations both IC and CG flashes are assumed to produce 500 moles of N.
Note: Lightning-NO production is proportional to flash channel length. W. Koshak of NASA-MSFC is calculating frequency distributions of flash channel lengths from the Lightning Mapping Array (LMA). In future simulations, we hope to use flash channel length PDFs to add variability to the lightning-NO produced per flash.

24. Vertical Distribution of LNOx Emissions Used in CMAQ
Vertical Distribution of VHF
Sources – Northern Alabama
Lightning Mapping Array
Apr.-Sept
Vertical distribution of
VHF sources from
Alabama LMA
is used along with a
direct relationship with
pressure to determine
the fraction of
emissions to put into
each layer from the
surface to the CMAQ-
predicted cloud top
When available, vertical
distributions of flash
channel length from the
LMA may provide more
accurate vertical
distribution information
Vertical
Distribution of
LNOx
Emissions
Used in CMAQ
D. Buechler, NASA/MSFC

25. Comparison of CMAQ-calc NOx with INTEX-A measurements
NOx DC-8 Flight 12 July 25, 2004
CMAQ
Without
Lightning NO
CMAQ
With
Lightning NO

26. Comparison of CMAQ-calc ozone with INTEX-A observations
Without
lightning
CMAQ
With
lightning

27. Comparison with INTEX-A NOx measurements

28. Comparison with INTEX-A ozone measurements
Low-bias in UT CMAQ-calc ozone also due to lack of
Stratospheric ozone and aircraft NOx emissions

29. CMAQ No
Lightning
SCIA
10:00 AM LT CMAQ output used
Tropp = 150 hPa
No averaging kernel applied
CMAQ
With
Lightning

30. Bias in
No Lightning
Run
Bias in
Run with
lightning

33. Summary Lightning-NO emission algorithm was added to CMAQ
Lightning-NO algorithm captures diel and day-to-day fluctuations in lightning flash rate
Addition of lightning-NO to CMAQ reduces low-bias between CMAQ-calc and measured NOx in UT. However, substantial low-bias still remains. Low-bias could be due to remaining errors in the source per flash but could also indicate that the NOx lifetime in the UT is too short in CMAQ and in other models.
Addition of lightning-NO reduces low-bias wrt SCIAMACHY in CMAQ-calculated tropospheric NO2 column from 22% to 5%.
Lightning-NO emissions in CMAQ contribute less than 2 ppbv of ozone to 8-hour maximum ozone on 75% of high ozone days

34. Future Work
Lightning-NO algorithm suitable for operational forecasts will be developed and tested (constrain using climatological flash rates)
Simulations with variable lightning-NO production per flash will be run (channel length PDFs of Koshak)
Simulations with more realistic vertical distribution of lightning-NO flashes will be run (addition of vertical layers in CMAQ; incorporation of vertical distribution of flash channel length information from Koshak)
Simulations including aircraft NO emissions will be run
Simulations of additional periods including 2006
Output from simulations will be used in inverse studies to constrain NO emissions and in nitrogen deposition investigations
Test WRF-Chem LNOx scheme of A. Hansen (FSU) – more microphysically based
Note: Support for this project provided by NASA’s Applied Sciences Air Quality Decision Support System Program.

36. Missing NO2 Aloft
When paired with aloft measurements from NASA INTEX, CMAQ underpredicts NO2 above the mixed layer
Consistent on all flights during the summer of 2004
On average 1.07 (1015 molecules cm-2)
Pinder et al., 2008

37. Lightning NO Production Scenarios
Summary of Five Midlatitude and Subtropical Storms
Orville et al., 2002
Means: 500 moles/flash
0.93 ratio
For global rate of 44
flashes/sec, this implies
~9 Tg N/yr

38. Comparison of CMAQ NOx with INTEX-A measurements

39. Comparison of CMAQ ozone with INTEX-A measurements

46. Note: CMAQ does not include a stratospheric source of ozone.
Upper tropospheric low-biases are expected.

49. Comparison with IONS ozonesondes over Houston, TX
Blue (No Lightning); Red (with Lightning), Black (IONS)