The ozone concentration in the tropical stratosphere peaks at 26 km, protecting life from harmful ultraviolet light without poisoning it. Climate models reproduce this peak, but textbook explanations yield errors of 10 km. Simplifying the well-understood sources and sinks of ozone, we develop a theory explaining that tropical ozone peaks where its dominant sink transitions from damping of atomic oxygen aloft (mainly via catalytic chemistry) to damping of ozone below (mainly via transport). 

The chemical composition of organic aerosol derived from wood-burning emissions under different burning conditions was characterised. Fresh emissions from flaming and smouldering were largely aromatic in nature, whereas upon aging the aromatic content decreased. This decrease was greater for smouldering due to the loss of toxic polyaromatic species, whereas under flaming conditions highly toxic polyaromatic species were produced. These differences present an important challenge for future policy.

Globally, lockdowns were implemented to limit the spread of COVID-19, leading to a decrease in emissions of key air pollutants. Here, we use novel satellite data and a chemistry model to investigate the impact of the pandemic on tropospheric ozone (O₃), a key pollutant, in 2020. Overall, we found substantial decreases of up to 20 %, two-thirds of which came from emission reductions, while one-third was due to a decrease in the stratospheric O₃ flux into the troposphere.

We studied the transport and chemical decomposition of volcanic SO₂, focusing on the 2019 Raikoke event. By comparing two different chemistry modeling schemes, we found that including complex chemical reactions leads to a more accurate prediction of how long SO₂ stays in the atmosphere. This research helps improve our understanding of volcanic pollution and its impact on air quality and climate, providing better tools for scientists to track and predict the movement of these pollutants.

Sunlight varies often and quickly under broken cloud cover, and every cloud field creates a unique pattern of sunlight on the surface below. These variations affect many processes in the Earth system, from photosynthesis and chemistry to cloud formation itself. The exact way in which cloud particles interact with sunlight is complex and expensive to calculate. We demonstrate a simplified framework which explains how sunlight changes for potentially any cloud field.

In 2020, regulations by the International Maritime Organization aimed to reduce aerosol emissions from ships. These aerosols previously had a cooling effect, which the regulations might reduce, revealing more greenhouse gas warming. Here we find that, while there is regional warming, the global 2020–2040 temperature rise is only +0.03 °C. This small change is difficult to distinguish from natural climate variability, indicating the regulations have had a limited effect on observed warming to date.

The impacts of biomass burning and anthropogenic emissions on high tropospheric ozone levels are not well studied in southern Africa. We combined model simulations with recent observations at the surface and from space to quantify tropospheric ozone and its drivers in southern Africa. Our work focuses on the impact of emissions from different sources at different spatial scales, contributing to a comprehensive understanding of air pollution drivers and their uncertainties in southern Africa.

The study explored urban air quality in Prague using low-cost sensors and highlighted the multivariate adaptive regression splines (MARS) correction method's effectiveness in enhancing accuracy. Results showed traffic's impact on nitrogen dioxide levels and atmospheric dynamics on particulate matter. The research confirmed MARS-corrected sensors as cost-effective for monitoring, despite challenges like sensor ageing and data quality control.

We investigate ice formation pathways in idealized convective clouds using a novel microphysics scheme that distinguishes between five ice classes each with their own unique formation mechanism. Ice crystals from rime splintering form the lowermost layer of ice crystals around the updraft core. The majority of ice crystals in the anvil of the convective cloud stems from frozen droplets. Ice stemming from homogeneous and deposition nucleation was only relevant in the overshoot.

There is uncertainty in the sources of Arctic cold-season (November–April) sea salt aerosols. Using a chemical transport model and satellite observations, we quantify Arctic-wide sea salt aerosol emissions from fractures in sea ice, called open sea ice leads, and their atmospheric chemistry impacts for the cold season. We show that sea ice leads contribute to Arctic sea salt aerosols and bromine, especially in under-observed regions.

Mobile CH₄ measurements were conducted at a wastewater treatment plant in Hangzhou in the summer and winter of 2023. A multi-source Gaussian plume model, combined with a genetic algorithm inversion framework, was used to locate major CH₄ sources at the plant and quantify emissions. Results indicate that the summer CH₄ emissions (603.33 ± 152.66 t a^-1) were 2.8 times as high as inventory values, and winter values (418.95 ± 187.59 t a^-1) were twice as high. The main sources were the screen and primary clarifier.

The chemical composition of fine particulate matter was studied in the megacity of São Paulo (Brazil) during a polluted period. Vehicular-related sources remain relevant; however, a high contribution of biomass burning was observed and correlated with sample ecotoxicity. Emerging biomass burning sources, such as forest fires and sugarcane-bagasse-based power plants, highlight the need for additional control measures alongside stricter rules concerning vehicular emissions.

We used ground-based remote sensing data from the Aerosol Robotic Network to examine long-term trends in aerosol characteristics. We found aerosol loadings generally decreased globally, and aerosols became more scattering. These changes are closely related to variations in aerosol compositions, such as decreased anthropogenic emissions over East Asia, Europe, and North America; increased anthropogenic sources over northern India; and increased dust activity over the Arabian Peninsula.