22 research outputs found
Measurement report: Atmospheric new particle formation at a peri-urban site in Lille, northern France
Formation of ultrafine particles (UFPs) in the urban atmosphere is expected
to be less favored than in the rural atmosphere due to the high existing
particle surface area acting as a sink for newly formed particles. Despite
large condensation sink (CS) values, previous comparative studies between
rural and urban sites reported higher frequency of new particle formation
(NPF) events over urban sites in comparison to background sites as well as
higher particle formation and growth rates attributed to the higher
concentration of condensable species. The present study aims at a better
understanding the environmental factors favoring, or disfavoring,
atmospheric NPF over Lille, a large city in the north of France, and to
analyze their impact on particle number concentration using a 4-year
long-term dataset.
The results highlight a strong seasonal variation of NPF occurrences with a
maximum frequency observed during spring (27 events) and summer (53 events). It was found that high temperature (T>295 K), low relative humidity (RH <45 %), and high solar radiation are ideal to observe
NPF events over Lille. Relatively high CS values (i.e., ∼2×10-2 s−1) are reported during event days suggesting that high CS does not inhibit the occurrence of NPF over the ATmospheric Observations in LiLLE (ATOLL) station. Moreover, the particle growth rate was positively correlated with temperatures most probably due to higher emission of precursors. Finally, the nucleation strength factor (NSF) was calculated to highlight the impact of those NPF events on particle number concentrations. NSF reached a maximum of four in summer, evidencing a huge contribution of NPF events to particle number concentration at this time of the year.</p
Pollen cytoplasmic granules induce heterogeneous nucleation of water droplets at low supersaturation
International audienc
New approach for the determination of aerosol refractive indices - Part II: Experimental set-up and application to amorphous silica particles
International audienceThis article is the Part II of a work aimed at proposing a new method for determining the optical constants of aerosols. The Part I detailed the theoretical and numerical basis of an algorithm devoted to retrieve the imaginary and the real part of complex refractive indices from extinction spectra of aerosols. This algorithm associates the Mie theory, the single subtractive Kramers-Kronig relation, and an optimal estimation method in an iterative process. This Part II presents the experimental set-up developed to record simultaneously high spectral resolution extinction spectra and size distributions of airborne silica particles. Extinction spectra are measured with a high spectral resolution on a broad spectral range, including both infrared (650 - 2 , 500cm-1) and UV-visible (9 , 000 - 32 , 500cm-1) spectral regions. Experimental data were used to retrieve the complex refractive indices of aerosol particles. By associating the numerical procedure presented in the first paper and this experimental set-up, complex refractive indices of silica spherical aerosol particles have been determined under controlled experimental conditions. Additional comparison between experimental and simulated extinction spectra from retrieved complex refractive indices shows that this new methodology provides optical properties representative of the material
Experimental study of the heterogeneous reactivity between atomic chlorine and palmitic acid films
AIR:EAU+RCI:VMEThe present study focuses on the heterogeneous reaction between gaseous atomic chlorine and solid palmitic acid films, used as a proxy of the fatty acids detected in atmospheric airborne particles. This reaction is investigated in a coated wall flow tube reactor coupled to a molecular beam mass spectrometer. The reactive surfaces were prepared by coating the inner surface of the reactor. The initial ClE (TM) and Cl-2 uptake coefficient measured for these heterogeneous reactions is found to be fast: gamma(o) (Cl) = 0.07. The rapid formation of hydrogen chloride corresponding with the disappearance of atomic chlorine is highlighted. Furthermore, the formation of new chlorinated species on the solid substrate has been detected by TOF SIMS analysis leading to an ageing process of the surface. A heterogeneous recombination of Cl atoms to Cl-2 molecules was observed for aged surfaces
Reactivity of chlorine radical with submicron palmitic acid particles: kinetic measurements and product identification
The heterogeneous reaction of Cl• radicals with submicron palmitic acid
(PA) particles was studied in an aerosol flow tube in the presence or in the
absence of O2. Fine particles were generated by homogeneous
condensation of PA vapours and introduced into the reactor, where chlorine
atoms were produced by photolysis of Cl2 using UV lamps surrounding the
reactor. The effective reactive uptake coefficient (γ) has been
determined from the rate loss of PA measured by gas chromatography–mass spectrometer (GC/MS) analysis of reacted
particles as a function of the chlorine exposure. In the absence of O2,
γ = 14 ± 5 indicates efficient secondary chemistry involving
Cl2. GC/MS analysis has shown the formation of monochlorinated and
polychlorinated compounds in the oxidized particles. Although the PA
particles are solid, the complete mass can be consumed. In the presence of
oxygen, the reaction is still dominated by secondary chemistry but the
propagation chain length is smaller than in the absence of O2, which
leads to an uptake coefficient γ = 3 ± 1. In the particulate
phase, oxocarboxylic acids and dicarboxylic acids were identified by GC/MS.
The formation of alcohols and monocarboxylic acids is also suspected. A reaction
pathway for the main products and more functionalized species is proposed.
All these results show that solid organic particles could be efficiently
oxidized by gas-phase radicals not only on their surface but also in bulk
by mechanisms which are still unclear. They help to understand the aging of
primary tropospheric aerosol containing fatty acids
Wind-induced mechanical rupture of birch pollen: Potential implications for allergen dispersal
Mechanical rupture of pollen grains after a mechanical shock against a solid surface was tested as a new approach to one of the mechanisms related to the release of allergen loaded particles from pollen. Birch pollen was aerosolized and sent into an impactor to mimic a shock against a surface (trees, soil, walls, etc.) at wind speeds of atmospheric-relevance. Small particles in the range of 1–2.5 µm were released subsequently to pollen impaction. The number of particles released increased with the velocity of impaction and with the water content of pollen. Damaged grains were observed by transmission electron microscopy and released particles are most likely cytoplasmic granules. This mechanism of pollen rupture and/or discharge may be of great importance in urban environment and may significantly contribute to thunderstorm-related allergic asthma and other associated pollen subparticles IgE mediated diseases