pH is a key property of ambient aerosols affecting many atmospheric processes. As aerosol pH is a non-conservative parameter, diverse averaging metrics and temporal resolutions may influence its calculation results from thermodynamic models. This technical note seeks to quantitatively evaluate the average pH using varied metrics and resolutions. The ultimate goal is to establish standardized reporting practices in future research endeavors.

The assumptions of chemical equilibrium of trace gases are widely used for retrieval of poorly measured characteristics of the mesosphere – lower thermosphere from rocket and satellite data and for study the HO_x – O_x chemistry and airglows. In this work, we analyze the fundamental aspects of chemical equilibrium of some trace gases and discuses their possible applications.

Citric acid participates in and enhances the multi-component nucleation of SA·AM·W_n·CA_m, SA·DMA·W_n·CA_m, and SA·AM·DMA·W_n·CA_m (m=0–1, n = 0–4) clusters using the M06-2X/6-311+G(2d, p) level. Three COOH and one OH groups of CA can act as both hydrogen donors and acceptors, participate in the formation of the hydrogen bonds, lower the nucleation barriers. Addition of a CA molecule to above clusters resulted in negative Gibbs free energies for all reactions.

Supercooled liquid fraction (SLF) in mixed-phase clouds is retrieved for the first time using passive geostationary satellite observations based on differences in liquid droplet and ice particle radiative properties. The retrieved results are well comparable to global distributions observed by active instruments, and the feasibility of the retrieval method to analyze the observed trends of SLF has been validated.

The Copernicus Atmosphere Monitoring Service (CAMS) provides global analyses and forecasts of aerosols and trace gases in the atmosphere. On 27/06/2023 a major upgrade, Cy48R1, became operational. Comparisons with in situ, surface remote sensing, aircraft, balloon and satellite observations, show that the new CAMS system is a significant improvement. The results quantify the skill of CAMS to forecast impactful events, such as wildfires, dust storms and air pollution peaks.

The distribution problems appear in atmospheric sciences at almost every corner for describing diverse processes. This manuscript presents a general formulation for addressing all these problem.

The great majority of observational trend studies of free tropospheric ozone use sparsely sampled ozonesonde and aircraft measurements as reference datasets. A ubiquitous assumption is that trends are accurate and reliable so long as long-term records are available. We show that sampling bias due to sparse samples can persistently reduce the trend accuracy, and highlight the importance of maintaining adequate frequency and continuity of observations.

To serve the uncertainty quantification (UQ) needs of data assimilation (DA) practitioners, we describe and justify a UQ algorithm from carbon flux inversion and incorporate its uncertainty into the final reported UQ. The algorithm is mathematically proved and its performance is shown on a carbon flux observing system simulation experiment. These results legitimize and generalize this algorithm’s current use and make available this effective algorithm to new DA domains.

Models are used to make forecasts of volcanic ash dispersion during eruptions. These models have unknown inputs relating to the eruption itself, physical processes, and meteorological conditions. We use statistical models to predict the output of the expensive physical model and show we can account for the effects of the different inputs. We compare the model to real-world observations and show that accounting for all sources of uncertainty may lead to different conclusions about the inputs.

The determination of ions in the mass spectra of individual particles remains uncertain. We have developed a standard-free mass calibration algorithm applicable to more than 98 % of ambient particles. With our algorithm, ions with ~0.05 Th mass difference could be determined. Therefore, many more atmospheric species could be determined and involved in the source apportionment of aerosols, the study of chemical reaction mechanisms, and the analysis of single-particle mixing states.

Chemistry-climate models show biases compared to surface ozone observations, and thus require bias-correction for impact studies and the assessment of air quality changes. We compare the performance of commonly used correction techniques for model outputs available via CMIP6. While all methods can reduce model biases, better results are obtained for more complex approaches. Thus, our study suggests broader use of these techniques in studies seeking to inform air quality management and policy.

An aerosol optical tweezer (AOT)-Raman spectroscopy system is developed to capture single aerosol droplet for phase transitions monitoring and morphology studies. Rapid droplet capture is achieved and accurate droplet size and refractive index are retrieved. Results indicate that inorganic/organic mixed droplets are more inclined to form core-shell morphology when RH decreases. The phase transitions of secondary organic aerosol/inorganic mixed droplets vary with their precursors.