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1.
Environ Sci Technol ; 53(22): 13257-13264, 2019 Nov 19.
Artigo em Inglês | MEDLINE | ID: mdl-31589819

RESUMO

Characteristic particle size, fluorescence intensity, and fluorescence spectra are important features to detect and categorize bioaerosols. A prototype size-resolved single-particle fluorescence spectrometer (S2FS) was developed to simultaneously measure aerodynamic diameters and fluorescence spectra. Emission spectra are dispersed in 512 channels from 370 to 610 nm, where a major portion of biological fluorescence emission occurs. The S2FS consists of an aerodynamic particle sizer and a fluorescence spectrometer with a 355 nm laser excitation source and an intensified charge-coupled device as the detector. Highly fluorescent particles, such as Ambrosia artemisiifolia pollen and Olea europaea pollen, can be distinguished by the S2FS on a single-particle level. For weakly fluorescent particles, fluorescence spectra can only be obtained by averaging multiple particles (between 100 and 3000) of the same kind. Preliminary ambient measurements in Mainz (Germany, central Europe) show that an emission peak at ∼440 nm was frequently observed for fluorescent fine particles (0.5-1 µm). Fluorescent fine particles accounted for 2.8% on average based on the number fraction in the fine mode. Fluorescent coarse particles (>1 µm) accounted for 8.9% on average based on the number fraction, with strongest occurrence observed during a thunderstorm and in the morning.


Assuntos
Laboratórios , Aerossóis , Europa (Continente) , Alemanha , Tamanho da Partícula , Espectrometria de Fluorescência
2.
Environ Sci Technol ; 53(21): 12506-12518, 2019 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-31536707

RESUMO

Highly oxygenated molecules (HOMs) play an important role in the formation and evolution of secondary organic aerosols (SOA). However, the abundance of HOMs in different environments and their relation to the oxidative potential of fine particulate matter (PM) are largely unknown. Here, we investigated the relative HOM abundance and radical yield of laboratory-generated SOA and fine PM in ambient air ranging from remote forest areas to highly polluted megacities. By electron paramagnetic resonance and mass spectrometric investigations, we found that the relative abundance of HOMs, especially the dimeric and low-volatility types, in ambient fine PM was positively correlated with the formation of radicals in aqueous PM extracts. SOA from photooxidation of isoprene, ozonolysis of α- and ß-pinene, and fine PM from tropical (central Amazon) and boreal (Hyytiälä, Finland) forests exhibited a higher HOM abundance and radical yield than SOA from photooxidation of naphthalene and fine PM from urban sites (Beijing, Guangzhou, Mainz, Shanghai, and Xi'an), confirming that HOMs are important constituents of biogenic SOA to generate radicals. Our study provides new insights into the chemical relationship of HOM abundance, composition, and sources with the yield of radicals by laboratory and ambient aerosols, enabling better quantification of the component-specific contribution of source- or site-specific fine PM to its climate and health effects.


Assuntos
Poluentes Atmosféricos , Material Particulado , Aerossóis , Pequim , China , Finlândia
3.
Phys Chem Chem Phys ; 21(37): 20613-20627, 2019 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-31528972

RESUMO

Atmospheric aerosol particles with a high viscosity may become inhomogeneously mixed during chemical processing. Models have predicted gradients in condensed phase reactant concentration throughout particles as the result of diffusion and chemical reaction limitations, termed chemical gradients. However, these have never been directly observed for atmospherically relevant particle diameters. We investigated the reaction between ozone and aerosol particles composed of xanthan gum and FeCl2 and observed the in situ chemical reaction that oxidized Fe2+ to Fe3+ using X-ray spectromicroscopy. Iron oxidation state of particles as small as 0.2 µm in diameter were imaged over time with a spatial resolution of tens of nanometers. We found that the loss off Fe2+ accelerated with increasing ozone concentration and relative humidity, RH. Concentric 2-D column integrated profiles of the Fe2+ fraction, α, out of the total iron were derived and demonstrated that particle surfaces became oxidized while particle cores remained unreacted at RH = 0-20%. At higher RH, chemical gradients evolved over time, extended deeper from the particle surface, and Fe2+ became more homogeneously distributed. We used the kinetic multi-layer model for aerosol surface and bulk chemistry (KM-SUB) to simulate ozone reaction constrained with our observations and inferred key parameters as a function of RH including Henry's Law constant for ozone, HO3, and diffusion coefficients for ozone and iron, DO3 and DFe, respectively. We found that HO3 is higher in our xanthan gum/FeCl2 particles than for water and increases when RH decreased from about 80% to dry conditions. This coincided with a decrease in both DO3 and DFe. In order to reproduce observed chemical gradients, our model predicted that ozone could not be present further than a few nanometers from a particle surface indicating near surface reactions were driving changes in iron oxidation state. However, the observed chemical gradients in α observed over hundreds of nanometers must have been the result of iron transport from the particle interior to the surface where ozone oxidation occurred. In the context of our results, we examine the applicability of the reacto-diffusive framework and discuss diffusion limitations for other reactive gas-aerosol systems of atmospheric importance.

4.
Science ; 359(6374): 411-418, 2018 01 26.
Artigo em Inglês | MEDLINE | ID: mdl-29371462

RESUMO

Aerosol-cloud interactions remain the largest uncertainty in climate projections. Ultrafine aerosol particles smaller than 50 nanometers (UAP<50) can be abundant in the troposphere but are conventionally considered too small to affect cloud formation. Observational evidence and numerical simulations of deep convective clouds (DCCs) over the Amazon show that DCCs forming in a low-aerosol environment can develop very large vapor supersaturation because fast droplet coalescence reduces integrated droplet surface area and subsequent condensation. UAP<50 from pollution plumes that are ingested into such clouds can be activated to form additional cloud droplets on which excess supersaturation condenses and forms additional cloud water and latent heating, thus intensifying convective strength. This mechanism suggests a strong anthropogenic invigoration of DCCs in previously pristine regions of the world.

5.
Nature ; 539(7629): 416-419, 2016 11 17.
Artigo em Inglês | MEDLINE | ID: mdl-27776357

RESUMO

The nucleation of atmospheric vapours is an important source of new aerosol particles that can subsequently grow to form cloud condensation nuclei in the atmosphere. Most field studies of atmospheric aerosols over continents are influenced by atmospheric vapours of anthropogenic origin (for example, ref. 2) and, in consequence, aerosol processes in pristine, terrestrial environments remain poorly understood. The Amazon rainforest is one of the few continental regions where aerosol particles and their precursors can be studied under near-natural conditions, but the origin of small aerosol particles that grow into cloud condensation nuclei in the Amazon boundary layer remains unclear. Here we present aircraft- and ground-based measurements under clean conditions during the wet season in the central Amazon basin. We find that high concentrations of small aerosol particles (with diameters of less than 50 nanometres) in the lower free troposphere are transported from the free troposphere into the boundary layer during precipitation events by strong convective downdrafts and weaker downward motions in the trailing stratiform region. This rapid vertical transport can help to maintain the population of particles in the pristine Amazon boundary layer, and may therefore influence cloud properties and climate under natural conditions.


Assuntos
Aerossóis/análise , Chuva , Aerossóis/química , Biomassa , Brasil , Fogo , Tamanho da Partícula , Compostos Orgânicos Voláteis/análise , Compostos Orgânicos Voláteis/química
6.
Proc Natl Acad Sci U S A ; 113(21): 5828-34, 2016 May 24.
Artigo em Inglês | MEDLINE | ID: mdl-26944081

RESUMO

Quantifying the aerosol/cloud-mediated radiative effect at a global scale requires simultaneous satellite retrievals of cloud condensation nuclei (CCN) concentrations and cloud base updraft velocities (Wb). Hitherto, the inability to do so has been a major cause of high uncertainty regarding anthropogenic aerosol/cloud-mediated radiative forcing. This can be addressed by the emerging capability of estimating CCN and Wb of boundary layer convective clouds from an operational polar orbiting weather satellite. Our methodology uses such clouds as an effective analog for CCN chambers. The cloud base supersaturation (S) is determined by Wb and the satellite-retrieved cloud base drop concentrations (Ndb), which is the same as CCN(S). Validation against ground-based CCN instruments at Oklahoma, at Manaus, and onboard a ship in the northeast Pacific showed a retrieval accuracy of ±25% to ±30% for individual satellite overpasses. The methodology is presently limited to boundary layer not raining convective clouds of at least 1 km depth that are not obscured by upper layer clouds, including semitransparent cirrus. The limitation for small solar backscattering angles of <25° restricts the satellite coverage to ∼25% of the world area in a single day.

7.
Science ; 337(6098): 1075-8, 2012 Aug 31.
Artigo em Inglês | MEDLINE | ID: mdl-22936773

RESUMO

The fine particles serving as cloud condensation nuclei in pristine Amazonian rainforest air consist mostly of secondary organic aerosol. Their origin is enigmatic, however, because new particle formation in the atmosphere is not observed. Here, we show that the growth of organic aerosol particles can be initiated by potassium-salt-rich particles emitted by biota in the rainforest. These particles act as seeds for the condensation of low- or semi-volatile organic compounds from the atmospheric gas phase or multiphase oxidation of isoprene and terpenes. Our findings suggest that the primary emission of biogenic salt particles directly influences the number concentration of cloud condensation nuclei and affects the microphysics of cloud formation and precipitation over the rainforest.


Assuntos
Atmosfera/química , Material Particulado/química , Potássio/química , Chuva/química , Árvores/química , Tamanho da Partícula , Sais/química , América do Sul
8.
Chem Commun (Camb) ; 46(15): 2605-7, 2010 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-20449322

RESUMO

Depending on the solvent used, the mono-stannylated FcSnCl(3) (1) reacts with Na(2)S to give ionic [Na(6)(Me(2)CO)(4)(OH(2))(6)] [(FcSn)(3)S(6)](2) (2), with a yet unprecedented thiostannate anion, or the adamantane-type Sn/S-cluster [(FcSn)(4)S(6)] (3). Complex 2 reacts readily with [Ni(acac)(2)], yielding the mixed-metallic complex [{Na(thf)(3.5)}(2){(FcSn)(8)Ni(3)S(16)}] x 2 THF (4 x 2 THF); the structures of 1-4 are discussed as well as Mössbauer spectra.

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