Large upper tropospheric ozone enhancements above midlatitude North America during summer: In situ evidence from the IONS and MOZAIC ozone measurement network

Abstract

The most extensive set of free tropospheric ozone measurements ever compiled across midlatitude North America was measured with daily ozonesondes, commercial aircraft and a lidar at 14 sites during July-August 2004. The model estimated stratospheric ozone was subtracted from all profiles, leaving a tropospheric residual ozone. On average the upper troposphere above midlatitude eastern North America contained 15 ppbv more tropospheric residual ozone than the more polluted layer between the surface and 2 km above sea level. Lowest ozone values in the upper troposphere were found above the two upwind sites in California. The upper troposphere above midlatitude eastern North America contained 16 ppbv more tropospheric residual ozone than the upper troposphere above three upwind sites, with the greatest enhancement above Houston, Texas, at 24 ppbv. Upper tropospheric CO measurements above east Texas show no statistically significant enhancement compared to west coast measurements, arguing against a strong influence from fresh surface anthropogenic emissions to the upper troposphere above Texas where the ozone enhancement is greatest. Vertical mixing of ozone from the boundary layer to the upper troposphere can only account for 2 ppbv of the 16 ppbv ozone enhancement above eastern North America; therefore the remaining 14 ppbv must be the result of in situ ozone production. The transport of NOx tracers from North American anthropogenic, biogenic, biomass burning, and lightning emissions was simulated for the upper troposphere of North America with a particle dispersion model. Additional box model calculations suggest the 24 ppbv ozone enhancement above Houston can be produced over a 10 day period from oxidation reactions of lightning NOx and background mixing ratios of CO and CH4. Overall, we estimate that 69–84% (11–13 ppbv) of the 16 ppbv ozone enhancement above eastern North America is due to in situ ozone production from lightning NOx with the remainder due to transport of ozone from the surface or in situ ozone production from other sources of NOx

Summertime impact of convective transport and lightning NO<sub>x</sub> production over North America: modeling dependence on meteorological simulations

“…Both models simulate that NO x concentrations decrease by a factor of >5 from the Southeast to the Northeast and Eastern Canada, much larger than a factor of 2 or less in the measurements. Similar large biases in the simulated south-to-north decrease of lightning NO x over Eastern North America can also be found in previous studies (e.g., Li et al, 2005;Hudman et al, 2007;Cooper et al, 2006 and. Figure 1a shows that convective mass fluxes in the upper troposphere in both WRF and MM5 are generally low over the Northeast.…”

“…Hudman et al (2007Hudman et al ( , 2009 found lightning can increase upper troposphere O 3 concentrations by 10-17 ppbv and Cooper et al (2006) found an increase of 11-13 ppbv on average and suggested a maximum of 24 ppbv based on the box model analysis during INTEX-A over the Eastern US. We find, here, that O 3 concentrations are increased by up to ∼20 ppbv (Fig.…”

“…Cooper et al (2009) presented a summary of many related observational and modeling studies over the US and suggested that lightning contributes to more than 80% of summertime NO x in the upper troposphere in the region. It also increases the concentrations of O 3 and PAN in the free troposphere (e.g., Labrador et al, 2004;Cooper et al, 2006;Hudman et al, 2007). Hudman et al (2007) found that lightning enhanced O 3 concentrations by 10-17 ppbv and PAN by 30% in the upper troposphere based on the INTEX-A measurements over Eastern North America and the Western North Atlantic Ocean during summer 2004 using the GEOS-CHEM model.…”

Transport analysis of ozone enhancement in Southern Ontario during BAQS-Met

“…However, the overall importance of stratospheric ozone intrusions to the tropospheric ozone budget depends on their distribution with geography and season, and on the fate of the exchanged air parcels, particularly their vertical penetration and residence time Cooper et al, 2004;Thompson et al 2007;Tarasick and Slater, 2008). For these reasons, at least in part, observational estimates of the stratospheric contribution vary widely (e.g., Bachmeier et al, 1994;Browell et al, 1994Browell et al, , 2003Mauzerall et al, 1996;Dibb et al, , 1997Dibb et al, , 2003Allen et al, 2003;Bazhanov and Rodhe, 1997;Elbern et al, 1997;Li et al, 2002;Cooper et al, 2006;Thompson et al 2007).…”

Sensitivity of tropical tropospheric composition to lightning NOx production as determined by replay simulations with GEOS‐5

“…Budget analyses performed by Zhang et al [2003] showed that lightning contributes more than 50% of the upper tropospheric NO x over the United States from April to November, impacting the upper tropospheric O 3 budget by as much as 30%. Combined measurement and modeling studies performed by Cooper et al [2006Cooper et al [ , 2007 [Jacob, 1999;Martin et al, 2000], and (c) isentropic cross-tropopause transport of O 3 from the stratosphere [Allen et al, 2003;Jing et al, 2005].…”