Study of the unknown HONO daytime source at a European suburban site during the MEGAPOLI summer and winter field campaigns

International audienceNitrous acid measurements were carried out during the MEGAPOLI summer and winter field campaigns at SIRTA observatory in Paris surroundings. Highly variable HONO levels were observed during the campaigns, ranging from 10 ppt to 500 ppt in summer and from 10 ppt to 1.7 ppb in winter. Significant HONO mixing ratios have also been measured during daytime hours, comprised between some tenth of ppt and 200 ppt for the summer campaign and between few ppt and 1 ppb for the winter campaign. Ancillary measurements, such as NOx , O3 , photolysis frequencies, meteorological parameters (pressure, temperature, relative humidity , wind speed and wind direction), black carbon concentration , total aerosol surface area, boundary layer height and soil moisture, were conducted during both campaigns. In addition, for the summer period, OH radical measurements were made with a CIMS (Chemical Ionisation Mass Spectrometer). This large dataset has been used to investigate the HONO budget in a suburban environment. To do so, calculations of HONO concentrations using PhotoStationary State (PSS) approach have been performed, for daytime hours. The comparison of these calculations with measured HONO concentrations revealed an underestimation of the calculations making evident a missing source term for both campaigns. This unknown HONO source exhibits a bell-shaped like average diurnal profile with a maximum around noon of approximately 0.7 ppb h−1 and 0.25 ppb h−1 , during summer and winter respectively. This source is the main HONO source during daytime hours for both campaigns. In both cases, this source shows a slight positive correlation with J (NO2) and the product between J (NO2) and soil moisture. This original approach had, thus, indicated that this missing source is photolytic and might be heterogeneous occurring at ground surface and involving water content available on the ground. Published by Copernicus Publications on behalf of the European Geosciences Union. 2806 V. Michoud et al.: Study of the unknown HONO daytime sourc

Glacier shrinkage will accelerate downstream decomposition of organic matter and alters microbiome structure and function.

peer reviewedThe shrinking of glaciers is among the most iconic consequences of climate change. Despite this, the downstream consequences for ecosystem processes and related microbiome structure and function remain poorly understood. Here, using a space-for-time substitution approach across 101 glacier-fed streams (GFSs) from six major regions worldwide, we investigated how glacier shrinkage is likely to impact the organic matter (OM) decomposition rates of benthic biofilms. To do this, we measured the activities of five common extracellular enzymes and estimated decomposition rates by using enzyme allocation equations based on stoichiometry. We found decomposition rates to average 0.0129 (% d-1 ), and that decreases in glacier influence (estimated by percent glacier catchment coverage, turbidity, and a glacier index) accelerates decomposition rates. To explore mechanisms behind these relationships, we further compared decomposition rates with biofilm and stream water characteristics. We found that chlorophyll-a, temperature, and stream water N:P together explained 61% of the variability in decomposition. Algal biomass, which is also increasing with glacier shrinkage, showed a particularly strong relationship with decomposition, likely indicating their importance in contributing labile organic compounds to these carbon-poor habitats. We also found high relative abundances of chytrid fungi in GFS sediments, which putatively parasitize these algae, promoting decomposition through a fungal shunt. Exploring the biofilm microbiome, we then sought to identify bacterial phylogenetic clades significantly associated with decomposition, and found numerous positively (e.g., Saprospiraceae) and negatively (e.g., Nitrospira) related clades. Lastly, using metagenomics, we found evidence of different bacterial classes possessing different proportions of EEA-encoding genes, potentially informing some of the microbial associations with decomposition rates. Our results, therefore, present new mechanistic insights into OM decomposition in GFSs by demonstrating that an algal-based "green food web" is likely to increase in importance in the future and will promote important biogeochemical shifts in these streams as glaciers vanish

Chimie rapide atmosphérique en périphérie de mégapoles : étude du bilan des radicaux et des sources d’acide nitreux

OH is the main oxidant of the troposphere during daytime hours. It is, thus, a key species for the complex atmospheric chemistry which involves other radical species and therefore leading to a radical cycle. This cycle is responsible for the transformation of the majority of the compounds emitted or formed in the atmosphere and thus of the formation of secondary pollutants, such as ozone and secondary organic aerosols which can have harmful effect on human health or important effects on climate. One of the main radical sources in the troposphere is the photolysis of nitrous acid. However, the intensity and the nature of the whole sources of HONO are still unknown.The aim of my thesis was, therefore, to study radical chemistry and nitrous acid chemistry in different environments in order to improve our understanding of oxidation processes occurring in the atmosphere. To answer to these objectives, this work was based on results obtained during field campaigns which took place in different environments and at different periods of year: the MEGAPOLI summer and winter campaign which took place in a suburban environments of Paris suburbs during the summer 2009 and the winter 2010 and finally the CalNEX campaign which took place in a polluted environment of the suburbs of Los Angeles during the spring 2010.Dealing with the results of these campaigns, a methodology consisting in the use of simple calculation such as the photostationnary state hypothesis or more complex approach such as a 0D box model containing a detailed chemical mechanism (the MCM) and being constrained with all the measurements, has been developed and compared with the measured radical concentrations in order to test our knowledge. The 0D box model, also, allowed studying the radical budget in these three environments. Finally, a comparison between the measured and calculated HONO concentrations for the three environments has been conducted. This comparison leads to the identification of an additional HONO source, which is probably of the same nature in the three environmentsLe radical OH est le principal oxydant de l'atmosphère diurne. Celui-ci est donc au cœur d'une chimie complexe mettant en jeu d'autres espèces radicalaires formant ainsi un cycle appelé cycle radicalaire. Il est ainsi responsable de la transformation de la majorité des composés émis ou formés dans l'atmosphère et donc de la formation de polluants secondaires, tels que l'ozone ou les aérosols organiques secondaires, pouvant avoir des effets très néfastes pour la santé humaines ou des effets non négligeables sur le climat. Une des principales sources conduisant à l'initiation de ce cycle est la photolyse de l'acide nitreux. Or, la nature et l'intensité des sources de l'acide nitreux sont encore sujettes à débat. L'objectif de ma thèse était donc d'étudier cette chimie radicalaire ainsi que la chimie de l'acide nitreux dans divers environnements afin d'améliorer la compréhension des processus d'oxydation sévissant dans l'atmosphère. Pour répondre à ces objectifs, ce travail de thèse s'est appuyé sur les résultats collectés lors de campagnes de terrains menées dans des environnements différents et à des saisons variées : les campagnes MEGAPOLI été et hiver qui se sont déroulées dans un environnement suburbain de la banlieue de Paris à l'été 2009 et à l'hiver 2010 et enfin la campagne CalNEX qui s'est déroulée dans un environnement pollué de la banlieue de Los Angeles durant le printemps 2010.En s'appuyant sur les résultats de ces campagnes, une méthodologie consistant en l'utilisation de calcul simple type hypothèse de l'état quasi-stationnaire ou plus complexe type modélisation 0D incluant un schéma chimique détaillé (le MCM) et contraint avec l'ensemble des mesures, a été développée et comparée avec les mesures de concentrations de radicaux afin de tester l'état de nos connaissances. Le modèle 0D a également permis d'étudier le bilan radicalaire dans ces trois environnements. Enfin, une comparaison des concentrations d'HONO mesurées et calculées pour les trois environnements a été menée, conduisant à l'identification d'une source additionnelle probablement de même nature dans les trois environnements étudié

Chimie rapide atmosphérique en périphérie de mégapoles : étude du bilan des radicaux et des sources d’acide nitreux

OH is the main oxidant of the troposphere during daytime hours. It is, thus, a key species for the complex atmospheric chemistry which involves other radical species and therefore leading to a radical cycle. This cycle is responsible for the transformation of the majority of the compounds emitted or formed in the atmosphere and thus of the formation of secondary pollutants, such as ozone and secondary organic aerosols which can have harmful effect on human health or important effects on climate. One of the main radical sources in the troposphere is the photolysis of nitrous acid. However, the intensity and the nature of the whole sources of HONO are still unknown.The aim of my thesis was, therefore, to study radical chemistry and nitrous acid chemistry in different environments in order to improve our understanding of oxidation processes occurring in the atmosphere. To answer to these objectives, this work was based on results obtained during field campaigns which took place in different environments and at different periods of year: the MEGAPOLI summer and winter campaign which took place in a suburban environments of Paris suburbs during the summer 2009 and the winter 2010 and finally the CalNEX campaign which took place in a polluted environment of the suburbs of Los Angeles during the spring 2010.Dealing with the results of these campaigns, a methodology consisting in the use of simple calculation such as the photostationnary state hypothesis or more complex approach such as a 0D box model containing a detailed chemical mechanism (the MCM) and being constrained with all the measurements, has been developed and compared with the measured radical concentrations in order to test our knowledge. The 0D box model, also, allowed studying the radical budget in these three environments. Finally, a comparison between the measured and calculated HONO concentrations for the three environments has been conducted. This comparison leads to the identification of an additional HONO source, which is probably of the same nature in the three environmentsLe radical OH est le principal oxydant de l'atmosphère diurne. Celui-ci est donc au cœur d'une chimie complexe mettant en jeu d'autres espèces radicalaires formant ainsi un cycle appelé cycle radicalaire. Il est ainsi responsable de la transformation de la majorité des composés émis ou formés dans l'atmosphère et donc de la formation de polluants secondaires, tels que l'ozone ou les aérosols organiques secondaires, pouvant avoir des effets très néfastes pour la santé humaines ou des effets non négligeables sur le climat. Une des principales sources conduisant à l'initiation de ce cycle est la photolyse de l'acide nitreux. Or, la nature et l'intensité des sources de l'acide nitreux sont encore sujettes à débat. L'objectif de ma thèse était donc d'étudier cette chimie radicalaire ainsi que la chimie de l'acide nitreux dans divers environnements afin d'améliorer la compréhension des processus d'oxydation sévissant dans l'atmosphère. Pour répondre à ces objectifs, ce travail de thèse s'est appuyé sur les résultats collectés lors de campagnes de terrains menées dans des environnements différents et à des saisons variées : les campagnes MEGAPOLI été et hiver qui se sont déroulées dans un environnement suburbain de la banlieue de Paris à l'été 2009 et à l'hiver 2010 et enfin la campagne CalNEX qui s'est déroulée dans un environnement pollué de la banlieue de Los Angeles durant le printemps 2010.En s'appuyant sur les résultats de ces campagnes, une méthodologie consistant en l'utilisation de calcul simple type hypothèse de l'état quasi-stationnaire ou plus complexe type modélisation 0D incluant un schéma chimique détaillé (le MCM) et contraint avec l'ensemble des mesures, a été développée et comparée avec les mesures de concentrations de radicaux afin de tester l'état de nos connaissances. Le modèle 0D a également permis d'étudier le bilan radicalaire dans ces trois environnements. Enfin, une comparaison des concentrations d'HONO mesurées et calculées pour les trois environnements a été menée, conduisant à l'identification d'une source additionnelle probablement de même nature dans les trois environnements étudié

Fast atmospheric chemistry in megapole's suburbs : study of radical budget and sources of nitrous acid

Le radical OH est le principal oxydant de l'atmosphère diurne. Celui-ci est donc au cœur d'une chimie complexe mettant en jeu d'autres espèces radicalaires formant ainsi un cycle appelé cycle radicalaire. Il est ainsi responsable de la transformation de la majorité des composés émis ou formés dans l'atmosphère et donc de la formation de polluants secondaires, tels que l'ozone ou les aérosols organiques secondaires, pouvant avoir des effets très néfastes pour la santé humaines ou des effets non négligeables sur le climat. Une des principales sources conduisant à l'initiation de ce cycle est la photolyse de l'acide nitreux. Or, la nature et l'intensité des sources de l'acide nitreux sont encore sujettes à débat. L'objectif de ma thèse était donc d'étudier cette chimie radicalaire ainsi que la chimie de l'acide nitreux dans divers environnements afin d'améliorer la compréhension des processus d'oxydation sévissant dans l'atmosphère. Pour répondre à ces objectifs, ce travail de thèse s'est appuyé sur les résultats collectés lors de campagnes de terrains menées dans des environnements différents et à des saisons variées : les campagnes MEGAPOLI été et hiver qui se sont déroulées dans un environnement suburbain de la banlieue de Paris à l'été 2009 et à l'hiver 2010 et enfin la campagne CalNEX qui s'est déroulée dans un environnement pollué de la banlieue de Los Angeles durant le printemps 2010.En s'appuyant sur les résultats de ces campagnes, une méthodologie consistant en l'utilisation de calcul simple type hypothèse de l'état quasi-stationnaire ou plus complexe type modélisation 0D incluant un schéma chimique détaillé (le MCM) et contraint avec l'ensemble des mesures, a été développée et comparée avec les mesures de concentrations de radicaux afin de tester l'état de nos connaissances. Le modèle 0D a également permis d'étudier le bilan radicalaire dans ces trois environnements. Enfin, une comparaison des concentrations d'HONO mesurées et calculées pour les trois environnements a été menée, conduisant à l'identification d'une source additionnelle probablement de même nature dans les trois environnements étudiésOH is the main oxidant of the troposphere during daytime hours. It is, thus, a key species for the complex atmospheric chemistry which involves other radical species and therefore leading to a radical cycle. This cycle is responsible for the transformation of the majority of the compounds emitted or formed in the atmosphere and thus of the formation of secondary pollutants, such as ozone and secondary organic aerosols which can have harmful effect on human health or important effects on climate. One of the main radical sources in the troposphere is the photolysis of nitrous acid. However, the intensity and the nature of the whole sources of HONO are still unknown.The aim of my thesis was, therefore, to study radical chemistry and nitrous acid chemistry in different environments in order to improve our understanding of oxidation processes occurring in the atmosphere. To answer to these objectives, this work was based on results obtained during field campaigns which took place in different environments and at different periods of year: the MEGAPOLI summer and winter campaign which took place in a suburban environments of Paris suburbs during the summer 2009 and the winter 2010 and finally the CalNEX campaign which took place in a polluted environment of the suburbs of Los Angeles during the spring 2010.Dealing with the results of these campaigns, a methodology consisting in the use of simple calculation such as the photostationnary state hypothesis or more complex approach such as a 0D box model containing a detailed chemical mechanism (the MCM) and being constrained with all the measurements, has been developed and compared with the measured radical concentrations in order to test our knowledge. The 0D box model, also, allowed studying the radical budget in these three environments. Finally, a comparison between the measured and calculated HONO concentrations for the three environments has been conducted. This comparison leads to the identification of an additional HONO source, which is probably of the same nature in the three environment

An Experiment to Study Atmospheric Oxidation Chemistry and Physics of Mixed Anthropogenic-Biogenic Air Masses in the Greater Paris Area

International audienc

Vertical Profiles of Pollution Particle Concentrations in the Boundary Layer above Paris (France) from the Optical Aerosol Counter LOAC Onboard a Touristic Balloon

International audienceAtmospheric pollution by particulate matter represents a significant health risk and needs continuous monitoring by air quality networks that provide mass concentrations for PM10 and PM2.5 (particles with diameter smaller than 10 µm and 2.5 µm, respectively). We present here a new approach to monitor the urban particles content, using six years of aerosols number concentration measurements for particles in the 0.2−50 µm size range. These measurements are performed by the Light Optical Aerosols Counter (LOAC) instrument onboard the tethered touristic balloon "Ballon de Paris Generali", in Paris, France. Such measurements have allowed us first to detect at ground a seasonal variability in the particulate matter content, due to the origin of the particles (anthropogenic pollution, pollens), and secondly, to retrieve the mean evolution of particles concentrations with height above ground up to 150 m. Measurements were also conducted up to 300 m above ground during major pollution events. The vertical evolution of concentrations varies from one event to another, depending on the origin of the pollution and on the meteorological conditions. These measurements have shown the interest of performing particle number concentrations measurements for the air pollution monitoring in complement with regulatory mass concentrations measurement, to better evaluate the intensity of the pollution event and to better consider the effect of smallest particles, which are more dangerous for human health

Implementation of an original approach on the Mines-Douai Comparative Reactivity Method (MD-CRM) instrument to identify part of the missing OH reactivity at an urban site

International audienc

Investigation of ambient OH reactivity at a receptor site impacted by industrial, urban and marine emissions: Identification of missing OH reactivity

International audienc

Investigation of ambient OH reactivity at a receptor site impacted by industrial, urban and marine emissions: Identification of missing OH reactivity

International audienc