Analysis of long-term observations of NO_x and CO in megacities and application to constraining emissions inventories

Birgit Hassler (1, 2) , Brian C. Mcdonald (1, 2) , Gregory J. Frost (1) , Agnes Borbon (3) , David C. Carslaw (4) , Kevin Civerolo (5) , Claire Granier (1, 2, 6) , Paul S. Monks (7) , Sarah Monks (1, 2) , David D. Parrish (1, 2) , Ilana B. Pollack (8, 1, 2) , Karen H. Rosenlof (1) , Thomas B. Ryerson (1) , Erika von Schneidemesser (9) , Michael Trainer (1)

1 ESRL - NOAA Earth System Research Laboratory
2 CIRES - Cooperative Institute for Research in Environmental Sciences
3 LaMP - Laboratoire de Météorologie Physique
4 WACL - Wolfson Atmospheric Chemistry Laboratories
5 NY DEC - New York State Department of Environmental Conservation
6 TROPO - LATMOS
7 Department of Chemistry [Leicester]
8 Department of Atmospheric Science [Fort Collins]
9 IASS - Institute for Advanced Sustainability Studies [Potsdam]

Long-term atmospheric NO_x/CO enhancement ratios in megacities provide evaluations of emission inventories. A fuel-based emission inventory approach that diverges from conventional bottom-up inventory methods explains 1970–2015 trends in NO_x/CO enhancement ratios in Los Angeles. Combining this comparison with similar measurements in other U.S. cities demonstrates that motor vehicle emissions controls were largely responsible for U.S. urban NO_x/CO trends in the past half century. Differing NO_x/CO enhancement ratio trends in U.S. and European cities over the past 25 years highlights alternative strategies for mitigating transportation emissions, reflecting Europe's increased use of light-duty diesel vehicles and correspondingly slower decreases in NO_x emissions compared to the U.S. A global inventory widely used by global chemistry models fails to capture these long-term trends and regional differences in U.S. and Europe megacity NO_x/CO enhancement ratios, possibly contributing to these models' inability to accurately reproduce observed long-term changes in tropospheric ozone.

Keywords: chemistry-climate models; megacities; emissions; inventories; long-term trends

Domains: Atmospheric and Oceanic Physics [physics.ao-ph]; Ocean, Atmosphere; Environmental Sciences

Birgit Hassler, Brian C. Mcdonald, Gregory J. Frost, Agnes Borbon, David C. Carslaw, et al.. Analysis of long-term observations of NO_x and CO in megacities and application to constraining emissions inventories. Geophysical Research Letters, 2016, 43 (18), pp.9920-9930. ⟨10.1002/2016GL069894⟩. ⟨insu-01371221⟩