2001

Résumé

L'année 2001 est une année commune qui commence un lundi. C'est la 2001 année de notre ère, la première année du , du et la de la décennie 2000-2009. Les attentats du 11 septembre, ainsi que le début de la seconde guerre d'Afghanistan, constituent les événements marquants de l’année et même des vingt dernières années. Les attentats du sont parfois considérés comme le fait déclencheur de la guerre contre le terrorisme et mis en parallèle avec la chute du mur de Berlin en 1989 qui a marqué la fin de la guerre froide. Autres calendriers L'année 2001 du calendrier grégorien correspond aux dates suivantes :

Calendrier chinois : 4698 / 4699 (le Nouvel An chinois 4699 de l’année du serpent de métal a lieu le )
Calendrier hébraïque : 5761 / 5762 (le tishri 5762 a lieu le )
Calendrier indien : 1922 / 1923 (le chaitra 1923 a lieu le )
Calendrier musulman : 1421 / 1422 (le mouharram 1422 a lieu le

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https://fr.wikipedia.org/wiki/2001

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Water content of ambient aerosol during the Pittsburgh air quality study

Satoshi Takahama

The aerosol water content and volumetric growth factors of fine particulate matter were measured during July-August 2001 and January-June 2002 in an urban park about 6 km from downtown Pittsburgh, Pennsylvania. Most of the aerosol during the study was transported to the region from other areas, and its composition and concentration were characteristic of the regional particulate matter in the northeastern United States. During the summer months the ambient aerosol practically always contained water even when the relative humidity ( RH) was as low as 30%. In contrast, during the winter the aerosol was dry below 60% RH. The spring months were characterized by a transitional behavior between these two states. The observed seasonal behavior can be explained by the aerosol acidity. The summer aerosol was acidic and retained water at low RH. The winter aerosol was neutral and became wet when the relative humidity reached the deliquescence point of ammonium nitrate. The observations during July 2001 were compared with the predictions of the thermodynamic Gibbs Free Energy Minimization (GFEMN) model and the aerosol inorganics model ( AIM), neglecting the organic aerosol contribution to water absorption. The models under-predicted water concentrations by about 35%, but no clear correlation between organic mass and the excess water was observed. On average, the contribution of the organics to water absorption appeared to be higher during the afternoon hours and when the aerosol was presumably more oxidized.

2005

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A thermodynamic model, the Gibbs Free-Energy Minimization model (GFEMN), was used to simulate the partitioning of PM2.5 nitrate aerosol and nitric acid using highly time-resolved inorganic measurements collected at the Pittsburgh Air Quality Study during July 2001 and January 2002. Model results were evaluated using independent, high time resolution measurements of aerosol nitrate. The mean observed concentration in July was 0.6 mug/m(3) and 2.1 mug/m(3) in January. Model predictions were in agreement with the observations within 0.5 mug/m(3) on average, with measurement uncertainties often accounting for these discrepancies. The simulations were run assuming particles were liquid in July for all relative humidities (RHs) and solid below 60% RH in January. For both seasons the assumed physical state did not influence considerably the overall agreement with observations. The assumption of particle mixing state did appear to influence model error; however, assuming that particles were externally mixed during low RH periods in July improved agreement significantly. The exceptional sensitivity of predicted aerosol nitrate to ammonia in western Pennsylvania suggests that reductions in PM2.5 may be assisted by reductions in ammonia emissions.

2004

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