Emissions of PM2.5 in the Northeastern US have declined by 18% between 2002 and 2013, based on an analysis of satellite data, primarily from urban areas. A paper from researchers at the Harvard Clean Air Research center and ACE center that applied the Particle Emission Inventories using Remote sensing (PEIRS) methodology shows spatial (at 1×1 km resolution) and temporal trends for NE regional emissions indicating a decrease of about 3.3 tons/yr/km2 over the 12-year periods. However, emissions reduction were not homogeneous, and driven by those in highly urbanized areas and major traffic corridors. The majority of the reduction was from cold-season emissions. Warm season emissions changed less and remain more similar between urban and rural areas. These results are useful to evaluate and improve the effectiveness of emission control strategies, though a cost-effective method that can be used even for sparsely populated areas.