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

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

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

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

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.

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) 1995-1999 data set, 3) OTD only samples a few percent of total flashes

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

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)

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

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

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

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.

Vertical Distribution of LNOx Emissions Used in CMAQ Vertical Distribution of VHF Sources – Northern Alabama Lightning Mapping Array Apr.-Sept. 2003-2005 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

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

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

Comparison with INTEX-A NOx measurements

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

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

Bias in No Lightning Run Bias in Run with lightning

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

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.

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

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

Comparison of CMAQ NOx with INTEX-A measurements

Comparison of CMAQ ozone with INTEX-A measurements

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

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