The shift towards electric vehicles is gaining momentum. This change highlights the need to understand non-tailpipe emissions, like those from brake wear.  It is important to look at nitrous acid (HONO), nitryl chloride (ClNO2), and dinitrogen pentoxide (N2O5). These are significant contributors to atmospheric radicals and nitrogen oxides. These substances drive the chemical reactions that worsen air quality.  It is known that there are gaps in measurements and model predictions. This is especially true for HONO, where the sources have been debated since the 1970s.  Recent studies have shown that automotive braking releases these reactive nitrogen species.  This was discovered using chemical ionization mass spectrometry with an iodide reagent ion.  The findings show that ceramic and semi-metallic brake pads produce significant amounts of HONO.  Smaller amounts of ClNO2 and N2O5 were also detected.

The formation of HONO is thought to occur in the hot air coming from the brake rotor. This process involves the reaction of NO2 with hydrogen atoms from volatile organic compounds. These compounds are released during braking.  This discovery means that brake emissions should be considered in urban air quality studies.  The results show that brake wear is a notable source of these pollutants.  This is important for cities with high traffic and poor air quality.  Understanding these emissions can help in developing better strategies to improve air quality.  It is also crucial for the future of electric vehicles, which will rely more on braking for energy recovery.

The findings raise questions about the overall impact of brake emissions on air quality.  It is clear that more research is needed to fully understand these processes.  This includes studying the effects of different brake materials and driving conditions.  The goal is to reduce the environmental impact of automotive braking.  This is a complex issue that requires a multi-disciplinary approach.  It involves chemistry, engineering, and environmental science.  The results of this study are a step towards a better understanding of brake emissions and their role in air quality.  It is a reminder that even small sources of pollution can have a significant impact.  This is especially true in urban areas, where air quality is a major concern.

Brake Fumes: The Hidden Air Quality Culprits

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