Final Report Summary - ANTARCTIC HONO (Measuring and modelling nitrous acid (HONO) emissions at Dome C, Antarctica)
Environment and climate of high-latitude regions are very fragile and very sensitive to any perturbations. The onset of the Antarctic ozone hole has clearly highlighted the delicate equilibrium of the atmosphere, even in areas located far away from industrialised regions. For being the most remote places of the world, these regions are also important witnesses of the ongoing global warming. Also what is taking place in polar regions is of great importance for the understanding of our planet; we still have much to learn from them. Yet, they are difficult to study due to the most extreme weather conditions which are encountered there, the long polar nights and the absence of conventional mean of transportation.
In this project the focus was made on atmospheric chemistry in continental Antarctica at the French-Italian Concordia station (75 degrees and 6 seconds S - 123 degrees and 21 seconds E). Atmospheric chemistry is a complex discipline as atmospheric level of traces gases - such as ozone, nitrogen oxides, volatile organic compounds (VOCs), hydroxyl (OH) radicals, etc. - is continuously changing due to the large amount of chemical reactions taking place in the atmosphere. To allow a precise understanding of the chemistry of one atmosphere, the most important trace gases must be measured together over the longest possible period of time. The aim of the project was to measure one of those compounds: nitrous acid (HONO).
Nitrous acid is thought to play an important role in atmospheric chemistry but is very difficult to measure. Its measured levels can be biased due to heterogeneous (gas / solid) reaction as soon as it comes into contact with any surface of the measuring device. Measuring device must therefore be carefully chosen to avoid such artefacts. In Antarctica, HONO levels are very low which again enhance the difficulty to measure this compound. For these reasons, HONO has only been measured rarely in Antarctica and to date using measuring device which might suffer from artefacts. In this project, HONO was measured for the first time in Antarctica using a long-path absorption photometer (LOPAP). This instrument has been intensively tested for known artefact and is able to measure very low level of nitrous acid. Deploying a LOPAP instrument in continental Antarctica is challenging as the instrument uses liquid solutions which need to be transported outside - where temperatures never raise above -20 degrees of Celsius - and back inside. An important part of this project was to prepare the instrument to the rough conditions it will have to experience. This preparation was a success as no problem due to the cold was encountered during the measurements campaigns.
Using the prepared LOPAP instrument, HONO was measured during two summer seasons (2010 - 2011 and 2011 - 2012) at Concordia. During the 2010 and 2011 season, it was possible to carry a few measurements at the coastal French base of Dumont d'Urville (66 degrees and 40 seconds S, 140 degrees and 1 second E) to allow a comparison between coastal and continental HONO levels. During the 2011 - 2012 campaign, HONO was measured together with important trace gases such as OH radicals, ozone, nitrogen oxides, formaldehyde, and hydrogen peroxide. All these compounds were measured in the frame of a large French national research programme called OPALE dedicated to the study of atmospheric oxidant in East Antarctica and from which the present ANTARACTIC HONO project could profit.
The first measurements at the Concordia station revealed high levels of HONO and consequently presume high levels of oxidants. This was confirmed by measurement of oxidants during the second campaign. It was also found that HONO levels vary from day to day with higher concentration when the wind speed is low and vice versa. HONO levels also tend to be lower when the sky is heavily clouded which suggest that HONO production at Concordia is driven by the sun light. Over a 24-hour period, HONO levels follow a reproducible diurnal cycle with two maxima, one in the morning and one in the evening. Model calculation could show that these two peaks are due to the particular dynamic of the atmosphere at Concordia and variation over the day of the so-called planetary boundary layer (PBL).
Measurements at the coastal base of Dumont d'Urville were of great interest for the understanding of the transport of HONO over the Antarctic continent. It was found that measured levels are higher when air masses reaching Dumont d'Urville are coming from the continent (i.e. coming from Concordia). This clearly suggest a strong HONO source on the continent - which was also revealed by the high levels measured at Concordia - compared to the coast. Production of a large amount of oxidant on the continent and its transport to the coast has a direct impact on climate. Indeed, phytoplankton emits dimethyl sulphide (DMS) which reacts with oxidants to form aerosols. Aerosols are known to interact with the climate in different manners.
These measurements and especially the one obtained during the second campaign - where HONO was measured together with many other trace gases - will allow better understanding atmospheric chemistry at Concordia. This is of great interest as the European project for ice coring in Antarctica (EPICA) project ice core was drilled at Concordia. From this ice core temperatures of the earth and concentration of the most important greenhouse effect gases were reconstruct over the last 800 000 years. There is still much to learn from this ice core, notably from the nitrate and sulphate records. However, to allow an interpretation of these two records, atmospheric chemistry and the transfer of chemical compounds from the atmosphere to the ice must be better understood.
In this project the focus was made on atmospheric chemistry in continental Antarctica at the French-Italian Concordia station (75 degrees and 6 seconds S - 123 degrees and 21 seconds E). Atmospheric chemistry is a complex discipline as atmospheric level of traces gases - such as ozone, nitrogen oxides, volatile organic compounds (VOCs), hydroxyl (OH) radicals, etc. - is continuously changing due to the large amount of chemical reactions taking place in the atmosphere. To allow a precise understanding of the chemistry of one atmosphere, the most important trace gases must be measured together over the longest possible period of time. The aim of the project was to measure one of those compounds: nitrous acid (HONO).
Nitrous acid is thought to play an important role in atmospheric chemistry but is very difficult to measure. Its measured levels can be biased due to heterogeneous (gas / solid) reaction as soon as it comes into contact with any surface of the measuring device. Measuring device must therefore be carefully chosen to avoid such artefacts. In Antarctica, HONO levels are very low which again enhance the difficulty to measure this compound. For these reasons, HONO has only been measured rarely in Antarctica and to date using measuring device which might suffer from artefacts. In this project, HONO was measured for the first time in Antarctica using a long-path absorption photometer (LOPAP). This instrument has been intensively tested for known artefact and is able to measure very low level of nitrous acid. Deploying a LOPAP instrument in continental Antarctica is challenging as the instrument uses liquid solutions which need to be transported outside - where temperatures never raise above -20 degrees of Celsius - and back inside. An important part of this project was to prepare the instrument to the rough conditions it will have to experience. This preparation was a success as no problem due to the cold was encountered during the measurements campaigns.
Using the prepared LOPAP instrument, HONO was measured during two summer seasons (2010 - 2011 and 2011 - 2012) at Concordia. During the 2010 and 2011 season, it was possible to carry a few measurements at the coastal French base of Dumont d'Urville (66 degrees and 40 seconds S, 140 degrees and 1 second E) to allow a comparison between coastal and continental HONO levels. During the 2011 - 2012 campaign, HONO was measured together with important trace gases such as OH radicals, ozone, nitrogen oxides, formaldehyde, and hydrogen peroxide. All these compounds were measured in the frame of a large French national research programme called OPALE dedicated to the study of atmospheric oxidant in East Antarctica and from which the present ANTARACTIC HONO project could profit.
The first measurements at the Concordia station revealed high levels of HONO and consequently presume high levels of oxidants. This was confirmed by measurement of oxidants during the second campaign. It was also found that HONO levels vary from day to day with higher concentration when the wind speed is low and vice versa. HONO levels also tend to be lower when the sky is heavily clouded which suggest that HONO production at Concordia is driven by the sun light. Over a 24-hour period, HONO levels follow a reproducible diurnal cycle with two maxima, one in the morning and one in the evening. Model calculation could show that these two peaks are due to the particular dynamic of the atmosphere at Concordia and variation over the day of the so-called planetary boundary layer (PBL).
Measurements at the coastal base of Dumont d'Urville were of great interest for the understanding of the transport of HONO over the Antarctic continent. It was found that measured levels are higher when air masses reaching Dumont d'Urville are coming from the continent (i.e. coming from Concordia). This clearly suggest a strong HONO source on the continent - which was also revealed by the high levels measured at Concordia - compared to the coast. Production of a large amount of oxidant on the continent and its transport to the coast has a direct impact on climate. Indeed, phytoplankton emits dimethyl sulphide (DMS) which reacts with oxidants to form aerosols. Aerosols are known to interact with the climate in different manners.
These measurements and especially the one obtained during the second campaign - where HONO was measured together with many other trace gases - will allow better understanding atmospheric chemistry at Concordia. This is of great interest as the European project for ice coring in Antarctica (EPICA) project ice core was drilled at Concordia. From this ice core temperatures of the earth and concentration of the most important greenhouse effect gases were reconstruct over the last 800 000 years. There is still much to learn from this ice core, notably from the nitrate and sulphate records. However, to allow an interpretation of these two records, atmospheric chemistry and the transfer of chemical compounds from the atmosphere to the ice must be better understood.