Environmental regulations on NO_x emissions from automobiles and power plants in the United States led to a reduction in NO₂ levels between 20 and 40% over American cities from 2005 to 2016.  In fact, the only significant increases over the U.S. occurred over areas of intensive oil and natural gas extraction in western North Dakota and western Texas, indicating an increase in activities and, subsequently, NO_x emissions from flaring of natural gas and the heavy machinery used to extract the oil and natural gas.  Significant decreases in Mexico occurred over Mazatlan and Guadalajara (−15-−20%) with insignificant changes over other cities.  Mexico City had considerable spatial heterogeneity in the changes in NO₂ levels, with large increases to the west and north of the city center and large decreases in the city center and to the northeast.

US Regional Decreases in NO₂, 2005-2016

The trend map of the United States shows the large decreases in nitrogen dioxide concentrations from 2005 to 2016. Only decreases are highlighted in this map.

Texas Regional Changes in NO₂, 2005-2016

The trend map for Texas shows the percent change in nitrogen dioxide concentrations from 2005 to 2016.

North Dakota Regional Changes in NO₂, 2005-2016

The trend map for North Dakota shows the percent change in nitrogen dioxide concentrations from 2005 to 2016.

NPP VIIRS Lights at Night

The NPP VIIRS Lights at Night show bright lights (circled) co-located with the increases in NO2 levels over three areas of oil and natural gas extraction activities in western Texas and western North Dakota.