Unexpectedly High Contribution of Organic Matter to Aerosol Liquid Water Content in the Subtropical Atmosphere: A Case Study of Shenzhen

Studying aerosol liquid water content (ALWC) in high-humidity, high-organic-aerosol atmospheric environments is critically important for understanding how organic matter regulates climatic and environmental effects. Here, using field observations and model simulations, we explored ALWC at a subtropical coastal site in Shenzhen. We employed a multipath ALWC calculation framework for a comprehensive closure study of ALWC and quantified the contribution of organic matter to ALWC. Results showed average ALWC during the observation period was 8.8 μg m⁻³ nearly equivalent to the dry aerosol mass. Unexpectedly, organics—accounting for over 70% of the total mass concentration of PM_2.5—contributed an average of 42% ± 15% to ALWC, representing the highest contribution reported to date in similar studies. This demonstrated that neglecting the organic compounds significantly underestimate ALWC, as was further revealed consequently reducing aerosol extinction capacity by approximately 17.2%. Unlike previous assumptions, we found that organic contribution highly depends on their hygroscopicity (κ_org) not mass fraction or ambient humidity. Our study highlights the significant role of organics in regulating aerosols liquid water content urging their inclusion in air quality and climate simulation models with the implementation of carbon reduction strategies.