CIMS instrument confirmed for BORTAS

CIMS stands for Chemical Ionisation Mass Spectrometry and this technique has been shown to be brilliantly versatile with the potential to measure a vast array of important atmospheric species. The system that will be used on the BORTAS flights (operated by the University of Manchester) this summer uses polonium-210, one of the 33 radioactive isotopes of polonium. The polonium-210 emits alpha particles which can knock electrons out of the nitrogen molecules that are present. These 'free' electrons are then captured by neutral molecules which become negatively charged. In this case it is the reagent gas CH₃I (methyl iodide) that captures the electron and dissociates giving negatively charged iodine atoms (I^-). This I^- then reacts with the species we want to detect and transfers the negative charge as shown below or attaches to the other species forming a negatively charged adduct such as HCN.I^-.

Because our compounds of interest are now negatively charged they can be separated according to their mass to charge ratio and then detected. Chemical ionisation is used because it is gentle giving little fragmentation (where the ion splits up creating many more ions with different mass to charge ratios which complicate the spectrum). I^- is used because it is fairly selective; it is unreactive with most compounds present in the atmosphere but reacts with the compounds we want to detect. So this set up will allow us to detect the sum of NO₃ and N₂O₅ (they rapidly interconvert), nitric acid, formic acid, propanoic acid, butanoic acid and HCN. HCN has been shown to be an important tracer for biomass burning (eg. see http://bit.ly/laf97J) so this measurement particularly is useful for us.

The CIMS instrument on board the UK Atmospheric Research Aircraft

Like the LIF instrument (see blog posts from 11th October 2010 and 11th June 2010), the CIMS was flown on the RONOCO flights in August and September last year and January this year. It was during these flights that a correlation between the NO₃ and N₂O₅ measured by broadband cavity enhanced absorption spectroscopy (BBCEAS, operated by the University of Cambridge) and a peak in the CIMS spectrum was noticed. Then through a comparison exercise carried out at the Facility for Airborne Atmospheric Measurements the University of Leicester's NO₃/N₂O₅ calibration unit was used to confirm that the suspected NO₃ peak was indeed due to the sum of NO₃ and N₂O₅.

 The top plot shows the time series from the CIMS suspected NO₃ peak and the BBCEAS NO₃ and the bottom plot shows the strength of the correlation between the two.

At the beginning of the post I mentioned the versatility of the CIMS technique so as an example here is a list of the species I haven't mentioned that can be measured using different reagent ions: SO₂, HO₂NO₂, PAN, PPN, MPAN, HOOH, CH₃C(O)OOH, HCl, ClONO₂, NH₃, DMSO, C₅H₈, HO₂ HO₂+RO₂, H₂SO₄, amines, various volatile organic compounds.

If you want to learn more about the CIMS or what the guys at University of Manchester do see this page and pages linked from it. Thanks to Jennifer Muller from the University of Manchester for the information on CIMS and the results from the RONOCO campaign.

Transit flight and Pico observatory fly-by

So the science team meeting was really good; as well as finding out a lot of important information about the BORTAS-B campaign this summer we saw some interesting data from the BORTAS-A campaign last summer. I will try and put together a series of posts over the next couple of weeks about what people had to say. The thing that I think was quite impressive was the number of people and organisations that were going to be involved this summer. So my first post concerns one data source which i think could prove quite valuable and which allows me to post some pretty pictures!


Obviously the aircraft has to get to Halifax somehow, and since the instruments are all onboard it seems sensible to make the most of the opportunity. This means that planning the transit flight is quite important as it gives us the opportunity to make some measurements further out in the Atlantic Ocean than will be possible from our base in Halifax. It has been decided that our route will probably look like this:

So we will fly from Cranfield, where the aircraft is based in the UK, to Porto in Portugal then to Pico in the Azores, St John's in Newfoundland and finally to Halifax in Nova Scotia. That might seem like a lot of stops but it gives us more flexibility in terms of doing maneuvers. This is important for the science as we will want to be able to look at changes in concentration at different heights and hopefully we will get lucky and intercept a forest fire plume. Even if we don't manage to see any forest fire emissions another brilliant opportunity is presented by the stop in Pico. There is an atmospheric observatory perched near the top of a dormant volcano on Pico Island which makes measurements of atmospheric composition. Details of the observatory are given here.

Pico Mountain showing the site of the Pico Mountain International Chemistry Observatory.

Measurements at this observatory no longer run continuously but they will be started in May 2011 and will run throughout the BORTAS-B campaign. The gas phase species that will be measured are carbon monoxide, ozone and non-methane hydrocarbons. The black carbon content and aerosol size will also be measured along with a number of meteorological parameters. Before landing at Pico Airport the aircraft will perform a circuit around the mountain and a height profile to see the changes in the composition of the air and physical parameters at different altitudes. This data can then be compared to the data from the observatory both providing context for the observatory measurements and allowing the two sets of instruments to be compared. 

 

 The instruments at the Pico Mountain International Chemistry Observatory.

Hopefully during the campaign the circulation of air will be such that air masses that we measure with the aircraft will travel on to be measured at the Pico observatory giving more information about how the plumes change with age. It is just a shame that I won't get the opportunity to go up and see the observatory (although I'm not sure how much I'd enjoy the steep trek up there) and the amazing views from the site.

The view from the observatory.

Thanks to Detlev Helmig from the Institute of Arctic and Alpine Research at the University of Colorado for pictures of the Pico Mountain Observatory.

Science Team Meeting

So we have the BORTAS science team meeting on Monday, Tuesday and Wednesday next week. It is taking place at the University of Edinburgh and will include discussions relevant to BORTAS-B, the campaign taking place this summer, and BORTAS-A, the campaign that went ahead last summer. The agenda is available at http://www.geos.ed.ac.uk/research/eochem/bortas/meetings/bortas-april-2011.html and anyone interested in watching online can contact Stephan Matthiesen whose details are on the above page.

There will be talks about the new instruments that have recently flown on the UK atmospheric research aircraft and whose performance is important for the BORTAS flights, and also talks about new instruments that will potentially be making their first real science flights during BORTAS. Presentations about the measurements that will be made across Canada and at the Pico Mountain Atmospheric Observatory on Pico Island in the Azores will also be made. And of course we will be deciding on a logo for the campaign so anyone involved who wants to submit a design better get designing fast. If you're coming I'll see you there, and if not then watch this space for an update on all the exciting news I'm expecting from the science team!

A Post for International Women's Day

So today is the hundreth international women's day. I was alerted to this by many different forums asking for suggestions of influential women in science, which got me thinking...I realised that I couldn't even name an influential female in the field of atmospheric science never mind tell you what their contribution was. I knew people whose work I had come across, whose research or attitude had impressed or inspired me but I wanted someone that would be widely accepted as an exceptional scientist...and if there was such a person shouldn't I have heard of them? So I asked around the people in my office to see if they could name any. Thankfully they seemed better educated than me and gave me two names to research, Susan Solomon and Julia Slingo.

Allegedly, Susan Solomon's interest in science began when watching The Undersea World of Jacques Cousteau however it wasnt biology she went on to study but atmospheric chemistry. She completed her PhD in 1981 at the University of California at Berkeley and then joined the National Oceanic and Atmospheric Administration (NOAA). The work that she is most famous for was her contribution to studies of the Antarctic ozone hole. She theorised that polar stratospheric clouds would provide solid surfaces on which the reactions of CFCs which destroy ozone could take place. The presence of a surface on which atoms can be immobilised greatly increases the rate at which these ozone destroying reactions can take place.

Polar stratospheric clouds

In August 1986 Solomon led an expedition to McMurdo Base, Antarctica to study the formation of the ozone hole. Not satisfied with just one trip she led another expedition in 1987 and from the two gathered enough measurements to show that chlorine dioxide was present at much greater concentrations than predicted, the first physical evidence pointing to chlorine chemistry as the cause of the ozone hole. Since then she has continued research at NOAA and was a co-chair of the Science Working Group I of the Intergovernmental Panel on Climate Change (IPCC). She has gained many awards for her work including the international Blue Planet Prize in 2004 and a share in the 2007 Nobel Peace Prize, she has even had an Antarctic glacier named after her.

The icebreaker USCGC Glacier approaching Winter Quarters Bay at McMurdo station, Antarctica 

Professor Julia Slingo is also an important figure in atmospheric science. She is now the Met Office Chief Scientist and before that she was the Director of Climate Research in NERC's National Centre for Atmospheric Science. Her background is in climate modelling and her research focuses on tropical climate variability and its influence and response to climate change. In 2006 she founded the Walker Institute for Climate System Research at the University of Reading. She was involved with the IPCC fourth assessment on climate change and in 2008 became the first woman President of the Royal Meteorological Society. Also in 2008 she received an OBE for her outstanding contribution to climate science.

Google Earth as a plume tracker

For 3 weeks in January I was involved in more chemistry flights on the BAE 146 Atmospheric Research Aircraft. The flights were part of the NERC funded ROle of Nighttime chemistry in controlling the Oxidising Capacity of the atmOsphere, RONOCO, field campaign. The idea was to fly through pollution plumes in the hope that we could see some interesting chemistry going on. The mission scientists (that is the people in charge of where we go and what we do during the flight) use cloud forecasts from the Met. Office Mesoscale Model and air quality forecasts from the Met. Office Unified Model amongst other things to decide where is the best place to fly.

On 17th January it was decided that we would do a dawn flight and try to follow a pollution plume that was forecast to be coming from Glasgow and Edinburgh and flowing out over the sea from the Firth of Forth.

 

Example of the plots available to the mission scientist with aerosol forecast on the left and cloud cover forecast on the right.

Take-off was at 06:00 so scientists were allowed onto the aircraft from 01:00 to allow time for instruments to warm up and be calibrated. We took off from East Midlands Airport (EMA) on time and headed up to 10 000 ft to allow in flight calibrations to be done. Once these were complete we went back to EMA; this may seem like a strange thing to do but it makes sense. At night the lowest altitude we can fly at is 1500 ft so if we want to find out about the structure of the atmosphere below that we need to do what is called a 'missed approach'. This is where we pretend to land at an airport but when we reach 50 ft the pilot pulls up and we take off again. This allows us to get a full vertical profile of the atmosphere and much more information. 

So having got information about the structure of the atmosphere we headed up north to look for our pollution. Once over the sea we could descend to 1500 ft hopefully allowing us to get into the more polluted air closer to the surface. As we approached the area where the plume was predicted we started to see concentrations rising indicating that we were indeed seeing something. We flew north across the plume until concentrations seemed to drop again and then flew back and forwards through the plume offsetting slightly each time so that we were slowly heading further out away from the coast. From the measurements we thought that we were getting a nice picture of the plume but its hard to see when you're looking at the data against time rather than location. This is where Google Earth comes in; Axel Wellpot who works for the Facility for Airborne Atmospheric Measurements (FAAM) had done some clever computing which enabled us to see our data superimposed on a map....and not only that but we could also show the predicted aerosol as well to compare what was seen with the predictions. Have a look at the pretty picture below to see how good it is at showing where we saw the plume.

This shows nitrogen oxides in light blue with higher concentrations shown as taller peaks. The colours underneath are the predicted aerosol with yellow being highest and blue lowest. You can see that the plume was pretty much where it was predicted.

Google Earth could then be used to plan our route back towards the coast flying through the peaks in pollution. So from first impressions it looks like a successful flight in terms of finding and sampling a plume but also a brilliant use of available software allowing the in flight data to tell us the best place to fly next. This could be useful for BORTAS where we will have predictions of where carbon monoxide is highest and will want to try and find those places and fly in and out of the plumes when we locate them.