scienceliberal
Urban Growth Fuels Hidden Air Chemistry in China
ChinaThursday, April 30, 2026
Key Findings
- Ground reactions dominate HONO production – over 50 % of total nitrous acid originates from surface chemistry.
- Urban expansion spikes HONO
- Beijing‑Tianjin‑Hebei: +50.3 %
- Yangtze River Delta: +48.4 %
- Pearl River Delta: +45.2 %
- Sichuan Basin: +38.1 %
- Vegetation shifts matter less – usually <5 % impact.
HONO’s Role in Nitrate Chemistry
| Time | Effect on NO₂ → HNO₃ | ΔNitrate (µg/m³) |
|---|---|---|
| Daytime | Higher HONO → more OH radicals, accelerating conversion | +0.8 (Beijing‑Tianjin‑Hebei), +0.6 (Yangtze), +0.3 (Pearl) |
| Nighttime | HONO competes with nitrate‑ion pathway, reducing conversion | –0.2 (Beijing‑Tianjin‑Hebei), –0.3 (Yangtze) |
Implications
- Urbanization changes atmospheric chemistry by increasing surface‑derived HONO, which in turn modifies nitrate levels.
- Air quality models must incorporate real‑time land use changes and refine surface chemistry rules to predict pollution accurately.
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