Mid-latitude lightning nitrogen oxides production efficiency

Inferred from Ozone Monitoring Instrument and World Wide Lightning Location Network (WWLLN) data

Scientific significance: Better knowledge of nitrogen oxides (NO_x = NO+NO₂ ) emissions from lightning (LNO_x) will improve confidence in the magnitude of production of ozone in the middle and upper troposphere, where the effect of ozone on radiative forcing maximizes. LNO_x influences the hydroxyl radical (OH), which is the primary tropospheric oxidant that plays a major role in determining the lifetime of methane, another important climate gas.

Method: We estimate the production efficiency (PE) of lightning NO_x (LNOx) using satellite data from the Aura Ozone Monitoring Instrument (OMI) and the ground-based World Wide Lightning Location Network (WWLLN) in three regions (Figure 1). Data were obtained over 5 boreal summers, 2007 – 2011, and comprise the largest number of mid-latitude convective events to date for estimating the LNO_x PE with satellite NO₂ and ground-based lightning measurements. The algorithm estimates freshly produced LNO_x by subtracting a background of aged NO_x estimated from the OMI dataset itself.

Results: We infer an average value of 180 ± 100 moles LNO_x produced per lightning flash. We also show evidence of a dependence of PE on lightning flash rate and find an approximate empirical power function relating moles LNO_x to flashes. PE decreases by an order of magnitude for a 2-order of magnitude increase in flash rate. This phenomenon has not been reported in previous satellite LNO_x studies but is consistent with ground-based observations suggesting an inverse relationship between flash rate and size.

Production of Lightning NO_x (LNO_x)

WWLLN Flash Counts

Mean daily data for JJA 2007 – 2011 per 1^o longitude×1^o latitude box, averaged over flashing boxes. (Top) LNO_x (104 moles), (bottom) mean daily WWLLN 1-hour flash counts (x100). The red boxes outline the 3 geographic regions examined.

LNO_x vs 1-hour flash rates

LNO_x (103 moles) vs 1-hour flash rates (103 kiloflashes) using data binned by flash count for (a) N. America, (b) Europe and (c) E. Asia. Blue and red lines are linear and power-function fits to the data, respectively.

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Summary:

Oxides of nitrogen are critical trace gases in the troposphere and are precursors for nitrate aerosol and ozone, which is an important pollutant and greenhouse gas. Lightning is the major source of NO_x (NO + NO₂ ) in the mid- to upper troposphere. We estimate the production efficiency (PE) of lightning NO_x (LNOx) using satellite data from the Ozone Monitoring Instrument (OMI) and the ground-based World Wide Lightning Location Network (WWLLN) in three northern mid-latitude, primarily continental regions that include much of North America, Europe and East Asia. Data were obtained over 5 boreal summers, 2007 – 2011 and comprise the largest number of mid-latitude convective events to date for estimating the LNO_x PE with satellite NO₂ and ground-based lightning measurements. The algorithm estimates freshly produced LNO_x by subtracting a background of aged NO_x estimated from the OMI dataset itself. We infer an average value of 180 ± 100 moles LNO_x produced per lightning flash. We also show evidence of a dependence of PE on lightning flash rate and find an approximate empirical power function relating moles LNO_x to flashes. PE decreases by an order of magnitude for a 2-order of magnitude increase in flash rate. This phenomenon has not been reported in previous satellite LNO_x studies but is consistent with ground-based observations suggesting an inverse relationship between flash rate and size.

Technical Description of Figures:

• Figure 1: (Top) LNO_x is an estimate of the moles of NO_x produced by recent lightning. It is derived by subtracting the product of the daily zonal mean OMI stratospheric NO₂ and stratospheric air mass factor from the total slant column NO₂ and dividing the result by an air mass factor appropriate for an NO₂ profile shape characteristic of a thunderstorm (containing a maximum in the mid to upper troposphere) and for converting LNO₂ to LNOx. Profiles of LNO and LNO₂ are obtained from GMI model simulations. Calculations are performed for all OMI pixels with Cloud Radiative Fraction > 0.97 and Optical Centroid Pressure < 500 hPa. Background NO_x is obtained from pixels that meet these same criteria but contain no flashes. Background is subtracted from LNO_x computed for pixels with flashes to obtain final LNO_x estimates. All calculations are performed using pixels mapped onto a 1 x 1 degree grid. A minimum of 3 pixels per grid cell is required to obtain a valid LNO_x estimate.
• Figure 1: (Bottom) WWLLN strokes are accumulated on the 1 x 1 degree grid over the hour prior to the OMI overpass and adjusted using detection efficiency factors derived from comparison of WWLLN strokes to OTD/LIS flash climatology. This adjustment also includes conversion of strokes to flashes.
• Figure 2: LNO_x (103 moles) vs 1-hour flash rates (103) using data binned by flash count for (a) N. America, (b) Europe and (c) E. Asia. Blue and red lines are linear and power-function fits to the data, respectively.

Scientific significance, societal relevance, and relationships to future missions:

Better knowledge of LNO_x will improve confidence in the magnitude of production of ozone in the middle and upper troposphere, where the effect of ozone on radiative forcing of climate maximizes. LNO_x also influences OH concentrations, which play a major role in determining the lifetime of methane. Methane is the second most important greenhouse gas and tropospheric ozone is the third most important.

Relevance for future science:

Increased accuracy of LNO_x production will be obtained through use of TROPOMI NO₂ columns and flashes from the Geostationary Lightning Mapper (GLM) onboard the GOES-16 and 17 satellites. This work is currently underway. Further refinement will be possible with the hourly NO₂ column data expected from NASA TEMPO (geostationary) beginning in 2022.

Data sources:

• Aura OMI Version 3.0 data: Total slant column, stratospheric vertical column
• Global Modeling Initiative (GMI) output: NO and NO₂ profiles from model simulations with and without lightning NO_x emissions
• World Wide Lightning Location Network (WWLLN): time series data sets of individual lightning strokes

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References:

Bucsela, E., K. Pickering, D. Allen, R. Holzworth, N. Krotkov, (2019), Mid-latitude lightning NO_x production efficiency inferred from OMI and WWLLN data, Journal of Geophysical Research – Atmospheres, https://doi.org/10.1029/2019JD030561.

Allen, D., K. Pickering, E. Bucsela, N. Krotkov, R. Holzworth, (2019), Lightning NO_x production in the tropics as determined using OMI NO₂ retrievals and WWLLN stroke data, Journal of Geophysical Research – Atmospheres, https://doi.org/10.1029/2018JD029824.

Pickering, K. E., E. Bucsela, D. Allen, A. Ring, R. Holzworth, and N. Krotkov (2016), Estimates of lightning NO_x production based on OMI NO₂ observations over the Gulf of Mexico, Journal of Geophysical Research - Atmospheres, 121, https://doi.org/10.1002/2015JD024179.

12.2019