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The sensitivity (S) of cloud parameters to the influence of different aerosol and meteorological parameters has in most previous aerosol–cloud interaction (aci) studies been addressed using traditional statistical methods. In the current study, relationships between cloud droplet effective radius (CER) and aerosol optical depth (AOD, used as a proxy for cloud condensation nuclei, CCN), i.e., the sensitivity (S) of CER to AOD, are investigated with different constraints of AOD and cloud liquid water path (LWP). In addition to traditional statistical methods, the geographical detector method (GDM) is applied in this study to quantify the relative importance of the effects of aerosol and meteorological parameters, as well as their interaction, on S. Moderate Resolution Imaging Spectroradiometer (MODIS) C6 L3 data and European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-5 reanalysis data, for the period from 2008 to 2022, were used to investigate aci over eastern China. Two contrasting areas were selected: the heavily polluted Yangtze River Delta (YRD) and a relatively clean area over the East China Sea (ECS). Linear regression analysis shows that CER decreases with the increase in AOD (negative S) in the moderately polluted atmosphere (0.10.3) over the YRD. Evaluation of S as function of the LWP shows that in the moderately polluted atmosphere over the ECS, S is negative in the LWP interval [40 gm-2 , 200 gm-2 ], and the sensitivity of CER to AOD is substantially stronger as LWP is larger. In contrast, in the polluted atmosphere over the YRD, S is positive in the LWP interval [0 gm-2 , 120 gm-2 ] and does not change notably as function of LWP in this interval. The study further shows that over the ECS, the CER is larger for higher low tropospheric stability (LTS) and relative humidity (RH) but lower for higher pressure vertical velocity (PVV). Over the YRD, there is no significant influence of LTS on the relationship between CER and AOD. The GDM has been used as an independent method to analyze the sensitivity of cloud parameters to AOD and meteorological parameters (RH, LTS and PVV). The GDM has also been used to analyze the effects of interactions between two parameters and thus obtain information on confounding meteorological effects on the aci. Over the ECS, cloud parameters are sensitive to almost all parameters considered except for cloud top pressure (CTP), and the sensitivity to AOD is larger than that to any of the meteorological factors. Among the meteorological factors, the cloud parameters are most sensitive to PVV and least sensitive to RH. Over the YRD, the explanatory power of the sensitivity of cloud parameters to AOD and meteorological parameters is much smaller than over the ECS, except for RH, which has a statistically significant influence on CTP and can explain 74 % of the variation of CTP. The results from the GDM analysis show that cloud parameters are more sensitive to the combination of aerosol and a meteorological parameter than to each parameter alone, but confounding effects due to co-variation of both parameters cannot be excluded. [ABSTRACT FROM AUTHOR]

Nitrogen dioxide (NO2) is a highly photochemically reactive gas, has a lifetime of only a few hours, and at high concentrations is harmful to human beings. Therefore, it is important to monitor NO2 with high-precision, time-resolved instruments. To this end, a Pandora spectrometer has been installed on the roof of the laboratory building of the Aerospace Information Research Institute of the Chinese Academy of Sciences in the Olympic Park, Beijing, China. The concentrations of trace gases (including NO2 , HCHO , O3) measured with Pandora are made available through the open-access Pandora database (https://data.pandonia-global-network.org/Beijing-RADI/Pandora171s1/ , last access: 11 July 2023). In this paper, an overview is presented of the Pandora total and tropospheric NO2 vertical column densities (VCDs) and surface concentrations collected during the first year of operation, i.e., from August 2021 to July 2022. The data show that NO2 concentrations were high in the winter and low in the summer, with a diurnal cycle where the concentrations reached a minimum during the daytime. The concentrations were significantly lower during the 2022 Winter Olympics in Beijing, showing the effectiveness of the emission control measures during that period. The Pandora observations show that during northerly winds, clean air is transported to Beijing with low NO2 concentrations, whereas during southerly winds, pollution from surrounding areas is transported to Beijing and NO2 concentrations are high. The contribution of tropospheric NO2 to the total NO2 VCD varies significantly on daily to seasonal timescales; i.e., monthly averages vary between 50 % and 60 % in the winter and between 60 % and 70 % in the spring and autumn. A comparison of Pandora-measured surface concentrations with collocated in situ measurements using a Thermo Scientific 42i-TL analyzer shows that the Pandora data are low and that the relationship between Pandora-derived surface concentrations and in situ measurements is different for low and high NO2 concentrations. Explanations for these differences are offered in terms of measurement techniques and physical (transport) phenomena. The use of Pandora total and tropospheric NO2 VCDs for validation of collocated TROPOspheric Monitoring Instrument (TROPOMI) data, resampled to 100 m × 100 m , shows that although on average the TROPOMI VCDs are slightly lower, they are well within the expected error for TROPOMI of 0.5 Pmolec.cm-2 + (0.2 to 0.5) ⋅ VCDtrop (1 Pmolec.cm-2 = 1 × 10 15 moleccm-2). The location of the Pandora instrument within a sub-orbital TROPOMI pixel of 3.5 km × 5.5 km may result in an error in the TROPOMI-derived tropospheric NO2 VCD between 0.223 and 0.282 Pmolec.cm-2 , i.e., between 1.7 % and 2 %. In addition, the data also show that the Pandora observations at the Beijing-RADI site are representative of an area with a radius of 10 km. [ABSTRACT FROM AUTHOR]

This review focuses on critical issues in ocean-atmosphere exchange that will be addressed by new research strategies developed by the international Surface Ocean-Lower Atmosphere Study (SOLAS) research community. Eastern boundary upwelling systems are important sites for CO2 and trace gas emission to the atmosphere, and the proposed research will examine how heterotrophic processes in the underlying oxygen-deficient waters interact with the climate system. The second regional research focus will examine the role of sea-ice biogeochemistry and its interaction with atmospheric chemistry. Marine aerosols are the focus of a research theme directed at understanding the processes that determine their abundance, chemistry and radiative properties. A further area of aerosol-related research examines atmospheric nutrient deposition in the surface ocean, and how differences in origin, atmospheric processing and composition influence surface ocean biogeochemistry. Ship emissions are an increasing source of aerosols, nutrients and toxins to the atmosphere and ocean surface, and an emerging area of research will examine their effect on ocean biogeochemistry and atmospheric chemistry. The primary role of SOLAS is to coordinate coupled multi-disciplinary research within research strategies that address these issues, to achieve robust representation of critical ocean-atmosphere exchange processes in Earth System models. © 2013 CSIRO.

Aerosol and cloud properties retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS) on-board the Aqua satellite were used to investigate aerosol-cloud interaction (ACI) over eastern China, using aerosol optical depth (AOD) as a proxy for the aerosol concentration, during a period of 15 years (2008-2022). Two contrasting areas were selected: the heavily polluted Yangtze River Delta (YRD) and a clean area over the East China Sea (ECS). Linear regression analysis shows the opposite behaviour of the cloud droplet effective radius (CER) and AOD relationship in the two different aerosol regimes. CER decreases with the increase of AOD in the moderately polluted atmosphere (0.10.3) over the YRD, CER increases with increasing AOD. Evaluation of the ACI index (here defined as the change in CER as a function of AOD) as function of the cloud liquid water path (LWP) shows that in the moderately polluted atmosphere over the ECS the ACI index is significant and positive in the LWP interval [40 g m-2, 200 g m-2], and increases substantially with increasing LWP. In contrast, in the polluted atmosphere over the YRD the ACI index is significant and negative in the LWP interval [0 g m-2, 120 g m-2] and does not change notably as function of LWP in this interval. To further analyse the influence of AOD and meteorological conditions on cloud parameters, the geographical detector method (GDM) has been used. The results show that all factors have a significant influence on the cloud parameters over the ECS, except for cloud top pressure (CTP), but the influence of AOD is larger than that of any of the meteorological factors. Among the meteorological factors, lower tropospheric stability (LTS) has the largest influence on the cloud parameters and relative humidity (RH) the smallest. Over the YRD, the explanatory power of the effect of AOD and meteorological parameters on cloud parameters is much smaller than over the ECS, except for RH which has a statistically significant influence on CTP and can explain 65% of the variation of CTP. The combined effect of meteorological factors and AOD on cloud parameters enhances the explanatory power over the effect of individual parameters. The study further shows that over the ECS the effect of RH and LTS on the CER/AOD relationship is opposite to that of pressure vertical velocity (PVV). Over the YRD, The CER is larger in unstable atmospheric conditions than in stable conditions, irrespective of the AOD and the CER is much larger in high relative humidity conditions than in low relative humidity conditions. [ABSTRACT FROM AUTHOR]