Megacity Emissions and Lifetimes of Nitrogen Oxides Probed from Space

Abstract

Megacities are immense sources of air pollutants, with large impacts on air quality and climate. However, emission inventories in many of them still are highly uncertain, particularly in developing countries. Satellite observations allow top-down estimates of emissions to be made for nitrogen oxides (NO(x) = NO + NO(2)), but require poorly quantified a priori information on the NO(x) lifetime. We present a method for the simultaneous determination of megacity NO(x) emissions and lifetimes from satellite measurements by analyzing the downwind patterns of NO(2) separately for different wind conditions. Daytime lifetimes are ~4 hours at low and mid-latitudes, but ~8 hours in wintertime for Moscow. The derived NO(x) emissions are generally in good agreement with existing emission inventories, but are higher by a factor of 3 for the Saudi Arabian capital Riyadh.

The Dawn of Geostationary Air Quality Monitoring: Case Studies From Seoul and Los Angeles

“…By providing the means to distinguish sources, long-term trends can be used to evaluate the changes of emissions driven by regulatory programs (Kim et al, 2006), technological controls (e.g., Russell et al, 2012), and economic activity (e.g., Russell et al, 2012;de Foy et al, 2016;Duncan et al, 2016). Whether considering daily measurements or analysis of long term monthly averages, instruments like OMPS NM provide a well-characterized, quantitatively stable measurement reflecting a balance of NO 2 emissions and removal at spatial scales of ∼25 km, with some limited information on pollutant transport (e.g., Beirle et al, 2011;Valin et al, 2013Valin et al, , 2014de Foy et al, 2016). As such, the measurements available from the past have not been sufficient to address the more pressing air quality management needs: the ability to distinguish sources within urban airsheds, characterization of local mesoscale flow patterns on pollutant transport, quantification of NO 2 removal mechanisms (e.g., Valin et al, 2013), or better characterization of photochemical ozone production to NO x (NO + NO 2 ) or VOC control strategies (e.g., Martin et al, 2004;Duncan et al, 2010;Jin et al, 2017;Schroeder et al, 2017).…”

“…Harmonizing atmospheric composition retrievals among LEO and GEO sensors is also necessary for effective utilization of the LEO and GEO measurements. The spatial (<10 km) and temporal (hourly) requirements for air quality measurements have largely been determined by the desire to resolve the processes affecting the emissions, lifetime and transport of tropospheric NO 2 (e.g., Beirle et al, 2011;Valin et al, 2011bValin et al, , 2013de Foy et al, 2015) because of its fundamental role in the formation of tropospheric O 3 and particulate matter. There have been a variety of approaches for validating NO 2 products retrieved from LEO platforms (e.g., Bucsela et al, 2008Bucsela et al, , 2013Irie et al, 2008;Boersma et al, 2009;Lamsal et al, 2010;Russell et al, 2011;Travis et al, 2016).…”

Systematic analysis of tropospheric NO&lt;sub&gt;2&lt;/sub&gt; long-range transport events detected in GOME-2 satellite data

“…The lifetime of NO 2 ranges from around 8 h in a typical planetary boundary layer scenario to a few days in the upper troposphere (Ehhalt et al, 1992;Beirle et al, 2011).…”

Tropospheric aerosol as a reactive intermediate

“…20 On this factual basis, we provide a novel interpretation of recently reported data on the quantication of the unknown HONO daytime source, 26 and seasonally-averaged daytime NO 2 decay lifetimes over several megacities. 51 …”