Revealing overlooked nitrous acid (HONO) pollution sources

What is it about?

In this study, we delved into the origins of a particular air pollutant called nitrous acid (HONO). To trace these origins, we employed a distinctive tool known as stable isotopic fingerprints (δ15N and δ18O). We investigated six potential sources where HONO emanates from and conducted a year-long analysis of its composition in both rural and urban environments. Interestingly, our investigations unveiled that livestock rearing, involving animals like pigs and chickens, contributes to the presence of HONO in the air. We also quantified the proportion of HONO released compared to another gas called ammonia (NH3). Furthermore, our discoveries indicated that the isotopic structure of HONO in the air fluctuates depending on the source and time of emission. By meticulously examining all potential sources of this pollution, we concluded that direct emissions from activities like farming are responsible for around 39~45% of the pollution in rural regions throughout the year. To substantiate our findings, we employed computer models, which corroborated the pivotal role of these direct sources in influencing the air quality in the North China Plain.

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Photo by Sabeer Darr on Unsplash

Photo by Sabeer Darr on Unsplash

Why is it important?

Hydroxyl radicals (OH) are crucial oxidizers in the atmosphere, playing a significant role in various chemical processes. During the daytime, OH forms mainly from the breakdown of HONO caused by sunlight. Historically, we believed that most HONO originated from secondary sources, like chemical reactions in the air, and paid less attention to direct emissions. This study employs distinctive indicators to trace the origins of HONO, revealing the impact of sources we previously overlooked, such as direct emissions, on the air we inhale. This new insight transforms our understanding of HONO's sources and equips us with valuable tools for future investigations into air quality.

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