Publications by authors named "Houssni Lamkaddam"

Organic compounds released from wildfires and residential biomass burning play a crucial role in shaping the composition of the atmosphere. The solubility and subsequent reactions of these compounds in the aqueous phase of clouds and fog remain poorly understood. Nevertheless, these compounds have the potential to become an important source of secondary organic aerosol (SOA).

View Article and Find Full Text PDF
Article Synopsis
  • * The study found that particle formation rates due to ion-induced processes are stable across temperature changes, while neutral particle formation rates increase significantly when temperatures drop from +10 °C to -10 °C.
  • * Despite higher ionization rates, the formation of charged clusters is unlikely to be enhanced in upper tropospheric conditions; instead, neutral nucleation is expected to dominate, with humidity having little effect unless extremely low.
View Article and Find Full Text PDF

Organic vapors from biomass burning are a major source of secondary organic aerosols (SOAs). Previous smog chamber studies found that the SOA contributors in biomass-burning emissions are mainly volatile organic compounds (VOCs). While intermediate volatility organic compounds (IVOCs) are efficient SOA precursors and contribute a considerable fraction of biomass-burning emissions, their contribution to SOA formation has not been directly observed.

View Article and Find Full Text PDF
Article Synopsis
  • Aerosols from gas-to-particle processes significantly contribute to urban smog and haze, particularly through the formation of ammonium nitrate, which can thrive in polluted city conditions.
  • Urban areas face complex variations in temperature and gas concentrations, influencing how quickly aerosols can form and grow.
  • Experimental results from CERN's CLOUD chamber reveal that rapid temperature fluctuations can enhance nanoparticle growth, highlighting the influence of inconsistent ammonia emissions in cities on aerosol dynamics.
View Article and Find Full Text PDF

Highly oxygenated organic molecules (HOMs) are a major source of new particles that affect the Earth's climate. HOM production from the oxidation of volatile organic compounds (VOCs) occurs during both the day and night and can lead to new particle formation (NPF). However, NPF involving organic vapors has been reported much more often during the daytime than during nighttime.

View Article and Find Full Text PDF

The main nucleating vapor in the atmosphere is thought to be sulfuric acid (HSO), stabilized by ammonia (NH). However, in marine and polar regions, NH is generally low, and HSO is frequently found together with iodine oxoacids [HIO, i.e.

View Article and Find Full Text PDF
Article Synopsis
  • The study investigates how high relative humidity (RH) influences the partitioning of biogenic oxidized organic molecules into secondary organic aerosols (SOA) using real-time measurements in a controlled lab setting.
  • Results show significant increases in SOA mass (45%-85%) as RH rises from low to high levels, with semi-volatile compounds playing a key role in this process.
  • The research explains that higher RH alters the chemical composition of aerosols, shifting toward more volatile species, and emphasizes the critical role of water content in promoting organic aerosol growth.
View Article and Find Full Text PDF

Iodine is a reactive trace element in atmospheric chemistry that destroys ozone and nucleates particles. Iodine emissions have tripled since 1950 and are projected to keep increasing with rising O surface concentrations. Although iodic acid (HIO) is widespread and forms particles more efficiently than sulfuric acid, its gas-phase formation mechanism remains unresolved.

View Article and Find Full Text PDF
Article Synopsis
  • Dimethyl sulfide (DMS) contributes to climate change by affecting cloud formation through its oxidation products, primarily methanesulfonic acid (MSA) and sulfuric acid (HSO), but predicting their levels accurately is difficult.
  • Experiments conducted at CERN's CLOUD chamber showed that lowering the temperature significantly boosts the production of MSA from DMS oxidation, while HSO production remains relatively stable, resulting in a lower HSO/MSA ratio at cold temperatures.
  • The research introduces a new DMS oxidation mechanism that increases MSA production estimates, significantly higher than previous models, revealing MSA's crucial role in the sulfur cycle and its impact on cloud condensation nuclei.
View Article and Find Full Text PDF
Article Synopsis
  • New particle formation events occur frequently in polluted environments, despite high loss rates of tiny clusters, suggesting scavenging by larger particles or unknown growth mechanisms might be less effective than anticipated.
  • Experiments in the CLOUD chamber at CERN showed that the creation of new particles from human-made vapors significantly drops when there are many pre-existing particles, proving they effectively scavenge smaller molecular clusters.
  • In conditions with high levels of nitric acid and ammonia, newly formed particles can grow rapidly and maintain their numbers, even in heavily polluted air, which helps explain why these particles survive in haze-like situations.
View Article and Find Full Text PDF

New particle formation in the upper free troposphere is a major global source of cloud condensation nuclei (CCN). However, the precursor vapours that drive the process are not well understood. With experiments performed under upper tropospheric conditions in the CERN CLOUD chamber, we show that nitric acid, sulfuric acid and ammonia form particles synergistically, at rates that are orders of magnitude faster than those from any two of the three components.

View Article and Find Full Text PDF
Article Synopsis
  • Aerosols significantly influence the Arctic atmosphere's radiation balance, with organic aerosols being a major component that remains poorly understood.
  • Analysis from eight Arctic observatories reveals that winter organic aerosols are primarily from anthropogenic sources in Eurasia, while summer sees a shift to natural emissions like marine and biogenic aerosols.
  • The strength and effects of these aerosol sources are influenced by environmental factors like nutrient levels, solar radiation, temperature, and snow cover, providing key insights for climate impact modeling in the Arctic.
View Article and Find Full Text PDF

Aerosol particles negatively affect human health while also having climatic relevance due to, for example, their ability to act as cloud condensation nuclei. Ultrafine particles (diameter < 100 nm) typically comprise the largest fraction of the total number concentration, however, their chemical characterization is difficult because of their low mass. Using an extractive electrospray time-of-flight mass spectrometer (EESI-TOF), we characterize the molecular composition of freshly nucleated particles from naphthalene and β-caryophyllene oxidation products at the CLOUD chamber at CERN.

View Article and Find Full Text PDF

Atmospheric secondary organic aerosol (SOA) undergoes chemical and physical changes when exposed to UV radiation, affecting the atmospheric lifetime of the involved molecules. However, these photolytic processes remain poorly constrained. Here, we present a study aimed at characterizing, at a molecular level and in real time, the chemical composition of α-pinene SOA exposed to UV-A light at 50% relative humidity in an atmospheric simulation chamber.

View Article and Find Full Text PDF

Aerosols still present the largest uncertainty in estimating anthropogenic radiative forcing. Cloud processing is potentially important for secondary organic aerosol (SOA) formation, a major aerosol component: however, laboratory experiments fail to mimic this process under atmospherically relevant conditions. We developed a wetted-wall flow reactor to simulate aqueous-phase processing of isoprene oxidation products (iOP) in cloud droplets.

View Article and Find Full Text PDF
Article Synopsis
  • - Iodic acid (HIO) can rapidly form aerosol particles in coastal areas, with nucleation rates surpassing those of sulfuric acid-ammonia under similar conditions.
  • - Ion-induced nucleation involves the initial formation of IO followed by the addition of HIO, occurring efficiently at temperatures below +10°C, while neutral nucleation relies on a different process involving iodous acid.
  • - Freshly formed HIO particles significantly contribute to fast particle growth and can effectively compete with sulfuric acid particle formation in unpolluted atmospheric regions.
View Article and Find Full Text PDF

Organic peroxy radicals (RO) play a pivotal role in the degradation of hydrocarbons. The autoxidation of atmospheric RO radicals produces highly oxygenated organic molecules (HOMs), including low-volatility ROOR dimers formed by bimolecular RO + RO reactions. HOMs can initiate and greatly contribute to the formation and growth of atmospheric particles.

View Article and Find Full Text PDF
Article Synopsis
  • New-particle formation significantly contributes to urban smog, and researchers investigated how this process occurs in cities, particularly in colder temperatures.
  • Experiments at CERN's CLOUD chamber revealed that below +5°C, nitric acid and ammonia vapors can rapidly condense onto new particles, stimulating high particle growth rates, especially below -15°C when they can nucleate directly into ammonium nitrate.
  • These findings suggest that in urban environments, especially during winter, vertical mixing and high local emissions can create conditions where these particles grow quickly, enhancing their chances of survival against scavenging.
View Article and Find Full Text PDF

Metal emissions are of major environmental and practical concern because of their highly toxic effects on human health and ecosystems. Current technologies available in the market for their detection are typically limited by a time resolution of 1 h or longer (e.g.

View Article and Find Full Text PDF

Reaction rate constants for the reaction of -dodecane with hydroxyl radicals were measured as a function of temperature between 283 and 303 K, using the relative rate method in the CESAM chamber (French acronym for "experimental multiphasic atmospheric simulation chamber"). The rate constants obtained at 283, 293, and 303 K are (1.27 ± 0.

View Article and Find Full Text PDF

We use a real-time temperature-programmed desorption chemical-ionization mass spectrometer (FIGAERO-CIMS) to measure particle-phase composition and volatility of nucleated particles, studying pure α-pinene oxidation over a wide temperature range (-50 °C to +25 °C) in the CLOUD chamber at CERN. Highly oxygenated organic molecules are much more abundant in particles formed at higher temperatures, shifting the compounds toward higher O/C and lower intrinsic (300 K) volatility. We find that pure biogenic nucleation and growth depends only weakly on temperature.

View Article and Find Full Text PDF

The temperature and concentration dependence of secondary organic aerosol (SOA) yields has been investigated for the first time for the photooxidation of n-dodecane (CH) in the presence of NO in the CESAM chamber (French acronym for "Chamber for Atmospheric Multiphase Experimental Simulation"). Experiments were performed with and without seed aerosol between 283 and 304.5 K.

View Article and Find Full Text PDF