Jos Lelieveld’s research while affiliated with Max Planck Institute for Chemistry and other places

Lightning is the most important source of nitric oxide (NO) in the tropical upper troposphere and controls the formation of tropospheric ozone (). It is associated with deep convection and occurs mostly over continents. The Chemistry of the Atmosphere Field Experiment in the Pacific (CAFE Pacific) was conducted in early 2024 from Cairns, Australia, taking airborne measurements across the Australian continent and the surrounding maritime regions. Based on cloud top properties, lightning data and in situ observations of NO, and carbon monoxide, we show that deep convection occurs over Northern Australia and the Indo‐Pacific Warm Pool. While we identify strong lightning activity over Australia, we observe deep convection in the Warm Pool that is not electrified. Our observations of low in the Warm Pool can be attributed to ‐poor air from the marine boundary layer, which is not replenished by photochemical production from NO at high altitudes.

Noncommunicable diseases (NCD) are the leading cause of premature death worldwide, accounting for over 38 million deaths annually, or approximately 70% of global mortality. The majority of these deaths are caused by cardiovascular diseases. The risk of NCD is closely linked to exposure to environmental stressors such as air pollution, noise pollution, artificial light at night and climatic changes, including extreme heat, sandstorms, and forest fires. In addition to traditional risk factors for cardiovascular diseases, such as diabetes, hypertension, smoking, hypercholesterolemia and genetic predisposition, there is increasing evidence that physicochemical environmental factors substantially contribute to the high numbers of NCD. Urbanization contributes to the amplification and accumulation of these stressors. This review summarizes the epidemiology and pathophysiology of environmental stressors with a particular focus on cardiovascular NCD. In addition, strategies and measures to reduce the impact of environmental risks, especially in the context of cardiovascular diseases, are discussed.

Ammonia (NH3) is an abundant alkaline gas in the atmosphere and a key precursor in the formation of particulate matter. While emissions of other aerosol precursors such as SO2 and NOx have decreased significantly, global NH3 emissions are stable or increasing, and this trend is projected to continue. This study investigates the impact of NH3 emission changes on size-resolved aerosol composition and acidity using the atmospheric chemistry-climate model EMAC. Three NH3 emission schemes are analyzed: two bottom-up inventories and one derived using an updated top-down method. The results reveal that sulphate-nitrate-ammonium aerosols in two fine mode size ranges (0–1 µm and 1–2.5 µm) show the greatest sensitivity to NH3 emission changes. Regional responses vary depending on the local chemical environment of secondary inorganic aerosols. In 'NH3-rich' regions (e.g. East Asia and Europe), the abundance of NH3 partially offsets the effects of reduced NH3 emissions when NOx and SO2 are available, especially for aerosols in the 1–2.5 µm range. This highlights the importance of coordinated control strategies for NH3, NOx and SO2 emissions. Further, we find that NH3 has a buffering effect in densely populated areas, maintaining aerosol acidity at moderate levels and mitigating drastic pH shifts. The study emphasizes that pH changes are closely related to NH3 emission variations, with the highest sensitivity observed in the fine mode size ranges. These results highlight the critical role of NH3 in shaping aerosol acidity and argue for size-specific approaches to managing particulate matter.

Biogenic volatile organic compounds (BVOCs) are emitted in large quantities from the terrestrial biosphere and play a significant role in atmospheric gaseous and aerosol compositions. Secondary organic aerosols (SOAs) resulting from BVOC oxidation affect the radiation budget both directly, through the scattering and absorption of sunlight, and indirectly, by modifying cloud properties. Human activities have extensively altered natural vegetation cover, primarily by converting forests into agricultural land. In this work, a global atmospheric chemistry–climate model, coupled with a dynamic global vegetation model, was employed to study the impacts of perturbing the biosphere through human-induced land use change, thereby exploring changes in BVOC emissions and the atmospheric aerosol burden. A land use scheme was implemented to constrain tree plant functional type (PFT) cover based on land transformation fraction maps from the year 2015. Two scenarios were evaluated: (1) one comparing present-day land cover, which includes areas deforested for crops and grazing land, with potential natural vegetation (PNV) cover simulated by the model, and (2) an extreme reforestation scenario in which present-day grazing land is restored to natural vegetation levels. We find that, compared to the PNV scenario, present-day deforestation results in a 26 % reduction in BVOC emissions, which decreases the global biogenic SOA (bSOA) burden by 0.16 Tg (a decrease of 29 %), while the total organic aerosol (OA) burden decreases by 0.17 Tg (a reduction of 9 %). On the other hand, the extreme reforestation scenario, compared to present-day land cover, suggests an increase in BVOC emissions of 22 %, which increases the bSOA burden by 0.11 Tg and the total OA burden by 0.12 Tg – increases of 26 % and 6 %, respectively. For the present-day deforestation scenario, we estimate a positive total radiative effect (aerosol + cloud) of 60.4 mW m⁻² (warming) relative to the natural vegetation scenario, while for the extreme reforestation scenario, we report a negative (cooling) effect of 38.2 mW m⁻² relative to current vegetation cover.

Noncommunicable diseases (NCDs) are responsible for the premature deaths of more than 38 million people each year, making them the leading cause of the global burden of disease, accounting for 70% of global mortality. The majority of these deaths are caused by cardiovascular diseases. The risk of NCDs is closely related to exposure to environmental stressors such as air pollution, noise pollution, artificial light at night, and climate change, including extreme heat, sandstorms, and wildfires. In addition to the traditional risk factors for cardiovascular diseases such as diabetes, high blood pressure, smoking, hypercholesterolemia and genetic predisposition, there is increasing evidence that physicochemical factors in the environment significantly contribute to the high NCD numbers. In addition, urbanization is related to the accumulation and intensification of these stressors. This expert review will summarize the epidemiology and pathophysiology of environmental stressors with a focus on cardiovascular NCDs. In addition, solutions and measures to mitigate the effects of environmental risks, especially concerning cardiovascular diseases, will be discussed.

This animation illustrates future summer warming in the Middle East and North Africa (MENA) relative to the pre-industrial climate (1850–1900). It also shows how the global annual mean temperature will change in future. Animation highlights when warming exceeds specific tipping points at national, regional, and global scales. The warming is based on the average of 21 statistically downscaled Global Climate Models at 31 km using a High-end greenhouse gas emission scenario (RCP—8.5). Please refer to the publication below for more information on temperature changes in MENA and globally. Cite: Malik, A., Stenchikov, G., Mostamandi, S., Parajuli, S., Lelieveld, J., Zittis, G., et al. (2024). Accelerated historical and future warming in the Middle East and North Africa. Journal of Geophysical Research: Atmospheres, 129, e2024JD041625. https://doi.org/10.1029/2024JD041625

Measurement of total peroxy nitrates (∑PNs) and alkyl nitrates (∑ANs) by instruments that use thermal dissociation (TD) inlets to convert the organic nitrate to detectable NO2 may suffer from systematic bias (both positive and negative) resulting from unwanted secondary chemistry in the heated inlets. Here we review the sources of the bias and the methods used to reduce it and/or correct for it and report new experiments using (for the first time) atmospherically relevant, unsaturated, biogenic alkyl nitrates as well as two different peroxyacetyl nitrate (PAN) sources. We show that the commonly used commercial C3-alkyl-nitrate (isopropyl nitrate, IPN) inlet for characterising the chemistry of ANs is not appropriate for real-air samples that contain longer chain nitrates. ANs generated in the NO3-induced oxidation of limonene are strongly positively biased in the presence of NO. By detecting NOX rather than NO2, we provide a simple solution to avoid the bias caused by the conversion of NO to NO2 by primary and secondary peroxy radicals resulting from the complex chemistry in the thermal degradation of long-chain, alkyl nitrates in air at TD-temperatures. We also show that using a photochemical source of PAN to characterise the TD-inlets can result in a much stronger apparent bias from NO to NO2 conversion than for a diffusion source of synthesised (“pure”) PAN at similar mixing ratios. This is explained by the presence of thermally labile trace gases such as peracetic acid (CH3C(O)OOH) and hydrogen peroxide (H2O2).

New particle formation (NPF) in the tropical upper troposphere is a globally important source of atmospheric aerosols1, 2, 3–4. It is known to occur over the Amazon basin, but the nucleation mechanism and chemical precursors have yet to be identified². Here we present comprehensive in situ aircraft measurements showing that extremely low-volatile oxidation products of isoprene, particularly certain organonitrates, drive NPF in the Amazonian upper troposphere. The organonitrates originate from OH-initiated oxidation of isoprene from forest emissions in the presence of nitrogen oxides from lightning. Nucleation bursts start about 2 h after sunrise in the outflow of nocturnal deep convection, producing high aerosol concentrations of more than 50,000 particles cm⁻³. We report measurements of characteristic diurnal cycles of precursor gases and particles. Our observations show that the interplay between biogenic isoprene, deep tropical convection with associated lightning, oxidation photochemistry and the low ambient temperature uniquely promotes NPF. The particles grow over time, undergo long-range transport and descend through subsidence to the lower troposphere, in which they can serve as cloud condensation nuclei (CCN) that influence the Earth’s hydrological cycle, radiation budget and climate1,4, 5, 6, 7–8.

Aircraft observations have revealed ubiquitous new particle formation in the tropical upper troposphere over the Amazon1,2 and the Atlantic and Pacific oceans3,4. Although the vapours involved remain unknown, recent satellite observations have revealed surprisingly high night-time isoprene mixing ratios of up to 1 part per billion by volume (ppbv) in the tropical upper troposphere⁵. Here, in experiments performed with the CERN CLOUD (Cosmics Leaving Outdoor Droplets) chamber, we report new particle formation initiated by the reaction of hydroxyl radicals with isoprene at upper-tropospheric temperatures of −30 °C and −50 °C. We find that isoprene-oxygenated organic molecules (IP-OOM) nucleate at concentrations found in the upper troposphere, without requiring any more vapours. Moreover, the nucleation rates are enhanced 100-fold by extremely low concentrations of sulfuric acid or iodine oxoacids above 10⁵ cm⁻³, reaching rates around 30 cm⁻³ s⁻¹ at acid concentrations of 10⁶ cm⁻³. Our measurements show that nucleation involves sequential addition of IP-OOM, together with zero or one acid molecule in the embryonic molecular clusters. IP-OOM also drive rapid particle growth at 3–60 nm h⁻¹. We find that rapid nucleation and growth rates persist in the presence of NOx at upper-tropospheric concentrations from lightning. Our laboratory measurements show that isoprene emitted by rainforests may drive rapid new particle formation in extensive regions of the tropical upper troposphere1,2, resulting in tens of thousands of particles per cubic centimetre.