Evidence of Heating-Dominated Urban NO Emissions

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Urban Planning

Background:

• Road transport emissions have decreased in high-income nations due to better exhaust technology.
• Despite reductions, urban air quality in many cities still exceeds World Health Organization (WHO) guidelines for pollutants like nitrogen dioxide (NO2), ozone (O3), and fine particulate matter (PM2.5).
• London has pioneered mobility interventions, including low-emission zones, to combat air pollution.

Purpose of the Study:

• To identify the primary source of nitrogen oxide (NOx) emissions in central London.
• To assess the impact of space heating on urban air quality.
• To inform future air quality management strategies and decarbonization efforts.

Main Methods:

• Utilized long-term air pollution flux measurements from a communications tower.
• Analyzed consumption and mobility data to support emission source identification.
• Quantified the contribution of natural gas combustion in boilers to NOx emissions.

Main Results:

• Space heating, specifically natural gas combustion in boilers, has become the dominant source of NOx emissions in central London.
• Natural gas boilers accounted for 72 ± 17% of NOx emissions between 2021-2023.
• Road transport is no longer the primary contributor to NOx emissions in the study area.

Conclusions:

• Urban air quality strategies must shift focus from road transport to building heating, particularly in cities reliant on natural gas.
• Decarbonization of the heat and power sector presents an opportunity for significant reductions in urban NOx emissions.
• The choice between low-carbon fuel combustion (e.g., hydrogen) and electrification (e.g., heat pumps) for heating will significantly impact future urban air quality and associated costs, with potential UK damage costs up to £600 million if hydrogen combustion replaces natural gas instead of heat pumps.