Observational evidence for aerosols increasing upper tropospheric humidity

Aerosol-cloud interactions are the largest source of uncertainty in the radiative forcing of the global climate. A phenomenon not included in the estimates of the total net forcing is the potential increase in upper tropospheric humidity (UTH) by anthropogenic aerosols via changes in the microphysics of deep convection. Using remote sensing data over the ocean east of China in summer, we show that increased aerosol loads are associated with an UTH increase of 2.2 +/- 1.5 in units of relative humidity. We show that humidification of aerosols or other meteorological covariation is very unlikely to be the cause of this result, indicating relevance for the global climate. In tropical moist air such an UTH increase leads to a regional radiative effect of 0.5 +/- 0.4 W m(-2). We conclude that the effect of aerosols on UTH should be included in future studies of anthropogenic climate change and climate sensitivity.Peer reviewe

New particle formation, growth and apparent shrinkage at a rural background site in western Saudi Arabia

Atmospheric aerosols have significant effects on human health and the climate. A large fraction of these aerosols originates from secondary new particle formation (NPF), where atmospheric vapors form small particles that subsequently grow into larger sizes. In this study, we characterize NPF events observed at a rural background site of Hada Al Sham (21.802 degrees N, 39.729 degrees E), located in western Saudi Arabia, during the years 2013-2015. Our analysis shows that NPF events occur very frequently at the site, as 73 % of all the 454 classified days were NPF days. The high NPF frequency is likely explained by the typically prevailing conditions of clear skies and high solar radiation, in combination with sufficient amounts of precursor vapors for particle formation and growth. Several factors suggest that in Hada Al Sham these precursor vapors are related to the transport of anthropogenic emissions from the coastal urban and industrial areas. The median particle formation and growth rates for the NPF days were 8.7 cm(-3) s(-1) (J(7)(nm)) and 7.4 nm h(-1) (GR(7-12nm)), respectively, both showing highest values during late summer. Interestingly, the formation and growth rates increase as a function of the condensation sink, likely reflecting the common anthropogenic sources of NPF precursor vapors and primary particles affecting the condensation sink. A total of 76 % of the NPF days showed an unusual progression, where the observed diameter of the newly formed particle mode started to decrease after the growth phase. In comparison to most long-term measurements, the NPF events in Hada Al Sham are exceptionally frequent and strong both in terms of formation and growth rates. In addition, the frequency of the decreasing mode diameter events is higher than anywhere else in the world.Peer reviewe

Observing air pollution from satellite: EUMETSAT contribution to air quality monitoring at the global scale

International audienceEUMETSAT’s (European Organisation for the Exploitation of Meteorological Satellites) contribution to global air quality monitoring is multifaceted, encompassing technological advancements, long-term commitments, and a collaborative approach to address environmental challenges.The organization has been actively involved in satellite observations since 1990 through programs like Meteosat and Metop, and since 2015, it has been contributing to the Copernicus EU program. This effort is particularly significant for supporting air quality monitoring in developing countries, where reliable in-situ observatories are limited, and there is high vulnerability to pollutants and climate change impacts. The data provision is set to continue for the next two decades thanks to next-generation missions such as Meteosat Third Generation (MTG). These missions, along with instruments like Sentinel-4 and Sentinel-5 under the Copernicus EU program, are dedicated to air quality monitoring in specific regions, including North Africa and globally.Here, we will showcase how the atmospheric composition data obtained from EUMETSAT's satellites can be utilized for air quality analysis at the continental and local scale. Recent scientific applications based on datasets from Infrared Atmospheric Sounding Interferometer (IASI) and Sentinel instruments will be reviewed. In addition, examples on how EUMETSAT's satellite data is used to monitor phenomena that have direct implications for health and security, such as desert dust storms and wildfire emissions. A critical part of the discussion will focus on the advantages and drawbacks of satellite data due to observational configurations. This may involve addressing challenges and limitations while highlighting the strengths of satellite observations for air quality monitoring. Finally, it will be shown the importance of data access and training for effective utilization of satellite data. Additional value can be derived from satellite information through techniques like data assimilation and the application of artificial intelligence and machine learning (AI-ML methods)