Tropospheric distribution and variability of N₂O: Evidence for strong tropical emissions

Abstract

[1] Measurements of atmospheric N 2 O spanning altitudes from the surface to 14 km, and latitudes from 67°S to 85°N, show high concentrations in the tropics and subtropics, with strong maxima in the middle and upper troposphere. The pattern varies significantly over time scales of a few weeks. Global simulations do not accurately capture observed distributions with latitude, altitude, or time. Inversion results indicate strong, episodic inputs of nitrous oxide from tropical regions (as large as 1 Tg N-N 2 O over 9 weeks) are necessary to produce observed vertical and latitudinal distributions. These findings highlight strong tropical sources of N 2 O with high temporal variability, and the necessity of using full vertical profile observations in deriving emissions from atmospheric measurements. Citation: Kort,

Consistency and quality assessment of the Metop-A/IASI and Metop-B/IASI operational trace gas products (O<sub>3</sub>, CO, N<sub>2</sub>O, CH<sub>4</sub>, and CO<sub>2</sub>) in the subtropical North Atlantic

“…we are not simply considering the annual mean latitudinal gradients). For N 2 O, the latitudinal relative difference between 20 and 40 • N is smaller than 0.32 % (Huang et al, 2008;Kort et al, 2011) and the seasonal cycle is insignificant as can be seen in WDCGG (2014). This implies a mean N 2 O gradient smaller than 0.016 % per degree of latitude.…”

Top-down constraints on global N<sub>2</sub>O emissions at optimal resolution: application of a new dimension reduction technique

“…In most cases in Fig. 4 we see that the model-measurement difference trends negative with height in the troposphere, which may reflect a model underestimate of the convective transport of N 2 O emissions (Kort et al, 2011). Large biases above 400 hPa in HIPPO IV (30-90 • N) and HIPPO V (30-90 • S) are driven by high-latitude observations in which the aircraft is sampling below the model tropopause but above the actual tropopause and highlight the difficulty in modeling the N 2 O vertical profile at these altitudes.…”

“…The aircraft payload included high-frequency N 2 O measurements by quantum cascade laser spectroscopy (Kort et al, 2011). To ensure calibration consistency we apply an offset adjustment to these data for each deployment based on concurrent flask-based air samples, which are anchored to the NOAA 2006A scale.…”

The importance of denitrification for N2O emissions from an N-saturated forest in SW China: results from in situ 15N labeling experiments

“…Soils under natural vegetation in tropical and subtropical regions have been reported to be a major source of nitrous oxide (N 2 O), a potent greenhouse gas and decomposer of ozone in the stratosphere (Hirsch et al 2006;Kort et al 2011;IPCC 2007). N 2 O emission from tropical forest are high compared to temperate and boreal natural ecosystems (Dalal and Allen 2008), but the contribution of subtropical forest in densely populated SE Asia to global N 2 O emissions is unclear.…”