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1.
Atmos Meas Tech ; 11(9): 5025-5048, 2018 Aug 31.
Artigo em Inglês | MEDLINE | ID: mdl-33868504

RESUMO

A new aircraft-mounted probe for collecting samples of cloud water has been designed, fabricated, and extensively tested. Following previous designs, the probe uses inertial separation to remove cloud droplets from the airstream, which are subsequently collected and stored for offline analysis. We report details of the design, operation, and modelled and measured probe performance. Computational fluid dynamics (CFD) was used to understand the flow patterns around the complex interior geometrical features that were optimized to ensure efficient droplet capture. CFD simulations coupled with particle tracking and multiphase surface transport modelling provide detailed estimates of the probe performance across the entire range of flight operating conditions and sampling scenarios. Physical operation of the probe was tested on a Lockheed C-130 Hercules (fuselage mounted) and de Havilland Twin Otter (wing pylon mounted) during three airborne field campaigns. During C-130 flights on the final field campaign, the probe reflected the most developed version of the design and a median cloud water collection rate of 4.5 mL min-1 was achieved. This allowed samples to be collected over 1-2 min under optimal cloud conditions. Flights on the Twin Otter featured an inter-comparison of the new probe with a slotted-rod collector, which has an extensive airborne campaign legacy. Comparison of trace species concentrations showed good agreement between collection techniques, with absolute concentrations of most major ions agreeing within 30 %, over a range of several orders of magnitude.

2.
Environ Sci Technol ; 44(21): 8128-33, 2010 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-20932002

RESUMO

The occurrence, source, and sink processes of N-nitrosodimethylamine (NDMA) have been explored by means of combined laboratory, field, and model studies. Observations have shown the occurrence of NDMA in fogs and clouds at substantial concentrations (7.5-397 ng L(-1)). Laboratory studies were conducted to investigate the formation of NDMA from nitrous acid and dimethylamine in the homogeneous aqueous phase. While NDMA was produced in the aqueous phase, the low yields (<1%) observed could not explain observational concentrations. Therefore gaseous formation of NDMA with partitioning to droplets likely dominates aqueous NDMA formation. Box-model calculations confirmed the predominant contributions from gas phase formation followed by partitioning into the cloud droplets. Measurements and model calculations showed that while NDMA is eventually photolyzed, it might persist in the atmosphere for hours after sunrise and before sunset since the photolysis in the aqueous phase might be much less efficient than in the gas phase.


Assuntos
Poluentes Atmosféricos/análise , Atmosfera/química , Dimetilnitrosamina/análise , Tempo (Meteorologia) , Movimentos do Ar , Poluentes Atmosféricos/síntese química , Poluentes Atmosféricos/química , Dimetilnitrosamina/síntese química , Dimetilnitrosamina/química , Monitoramento Ambiental , Cinética , Modelos Químicos , Fotólise , Vapor/análise
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