Ice nucleation observation raw data
Description
This study used a novel designed experimental setup to online measure the INPs concurrently for the ambient and heated aerosols (at 350 ℃), using a continuous flow diffusion chamber (CFDC) and other composition measurements. The difference between both measurements reflects the IN activities for non-refractory OA. We found the more oxygenated OA produced by photooxidation at noon preferentially acted as INPs. Our results give first direct evidence that the organic aerosols from anthropogenically polluted region could importantly contribute to the INPs well above the homogeneous ice nucleation temperature, when in high oxidation state and lower ambient relative humidity. Considering the abundant OA loadings over global scale, the role of OA in modulating ice number concentration and its potential consequent impacts on weather and climate should be attended.
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The field experiment in this study was conducted at the Beijing Cloud Laboratory and Observational Utilities Deployment Base (CLOUD Base) from 4th to 26th Sep. 2020, which is located about 65 km northwest of the center of Beijing, where the local emissions are mainly from industrial factory, residence and traffic, which is a typical sub-urban site. We aim to identify the role of INPs for particles with different levels of volatility, a catalytic striper (CS) instrument (CS015, Catalytic Instruments Inc, Germany) is used to remove the non-refractory components in particles which can evaporate at 350 ℃. The advantage of CS compared to the thermo-denuder is the evaporated gas can be rapidly catalyzed as hydrocarbon, avoiding the potential recondensation of gases to particle phase when heated sample passed through a cooled environment . The sampling after CS ascertains only aerosols with vaporization temperature higher than 350 ℃ are measured, which will not include most ammonium inorganic salt, but black carbon (BC) and some organic aerosol (OA) will retain. These particles surviving after CS are designated as refractory (RE) substance. The exact definition of threshold temperature for refractory component may be at 600 ℃ , higher than the operation temperature here, but previous studies using thermodenuder (usually operate up to 250 ℃) showed an over 90% of aerosol substances could be already removed. Ambient INP concentration was measured online by a continuous flow diffusion chamber ice activation spectrometer (CFDC-IAS, Handix Scientific Inc, USA). The principals of the CFDC-IAS is identical to the Colorado State University (CSU) CFDC , and can additionally achieve continuous online measurement of ambient INPs, which had previous field deployment in Beijing. The aerosol chemical compositions which can vaporize at 600 ℃, including ammonium sulphate, nitrate and organic aerosol was measured by a high resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS, Aerodyne Inc, USA). The composition of BC mass and number concentration was measured by a single particle soot photometer (SP2, DMT Inc, USA) . In addition, the SP2 can also measure the scattering particle, and is able to discriminate the BC and non-BC particles according to the presence of the incandescence signal.