Impact of Changes in Barometric Pressure
on Landfill Methane Emissions
Liukang Xu
February 29, 2012
TRANSCRIPT
SLIDE 1 [00:00-00:42]:
Moderator:
Let’s turn the control over to our speaker.
Speaker:
Thanks, Ashlee, and I am glad to be here to discuss the research results we obtained two years ago; and
the title of my Webinar is: “Impact of Changing the Barometric Pressure on the Landfill Methane
Emissions”. And, I want to say thank you for my colleagues: Jim Amen, Xiaomao Lin, and, also, Karla
Welding, she is superintendent at the landfill in Lincoln, Nebraska.
SLIDE 2 [00:42]:
Why do we want to spend the time and effort to study how the barometric pressure regulates a landfill
emission?
SLIDE 3, 4 [00:58, 01:08]:
Here I listed a few reasons in discussion here. The first one is for modeling study. You know, you need
to understanding how the environmental variable regulates landfill emissions in order to get a good
model to model that methane emission from the landfill at different times of the year, at different times
of the day; and also for the landfill owner and also the superintendent to determine that the mitigation
strategy, you need understanding, you know, all the processing before you can have a good strategy.
It’s also very essential for the government to formulating the control and all the regulation especially
from the EPA.
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Impact of Changes in Barometric Pressure
on Landfill Methane Emissions
Liukang Xu
February 29, 2012
SLIDE 5 [01:50]:
Quite a few topic I want to cover today in this webinar. The first one is methane is a very strong
greenhouse gas; then, the second one I will briefly discuss the Eddy Covariance and Flux Method; the
third one is the methane emission we measured at Bluff Road Landfill near Lincoln, Nebraska; the fourth
I will present some of the results, and to show how pressure changing regulates the methane emission;
and at the end I will discuss some of the implications from our results.
SLIDE 6 [02:36]:
From this table we can see how much Greenhouse Effect from these three major greenhouse gases. We
all know that CO 2 is the strongest one; the current level in the atmosphere is about 380 ppm,
contributes 1.68 watts per square meter(W m2) and radiates to forcing to the atmosphere. This number
is averaging over the whole global. Methane, we have about like 1.8 ppm; but we have 0.48 W m2,
Radiative Forcing to the atmosphere. The third one is nitrous oxide which had 0.16 W m2. So,
understanding the methane, the balance the atmosphere is very critical to understanding how changing
the methane concentration would impact our climate.
SLIDE 7 [03:57]:
Where does all this methane come from? This chart will show you, on average globally, on average, the
major source of the methane to the atmosphere coming from wetland, about 22%; rice fields, especially
in Southeast Asia, about 21%; and some other source like biomass burning and domestic animal, also
landfill, 7.7%. This is averaged over the whole world, but in the United States, we have like about 23%)
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Impact of Changes in Barometric Pressure
on Landfill Methane Emissions
Liukang Xu
February 29, 2012
of the methane coming from landfills. The oil and gas industry and insects and termites, other insects,
also produce methane.
SLIDE 8 [05:11]:
We used the Eddy Covariance method to measure the methane emission from the landfill, and before I
present our results, it might be a good time to stop for a poll question.
SLIDE 9 [05:32]: POLL QUESTION
Moderator:
All right, Liukang. I will pop up the poll question for our audience. It looks like it says, “Are you familiar
with this EC method?" and you can choose from: No. It’s new to me; Yes, but I’ve never used it; and
Yes. I am using it now. So, go ahead and pick an answer and we will give everyone a few moments to
finish.
Brief pause
POLL RESPONSE(slide not shown)
SLIDE 10 [06:11]:
Speaker:
Thanks for the response and as expected not a whole lot of people in this group familiar with this Eddy
Covariance Method. The EC Method or Eddy Covariance Method has been used over the agricultural
field; natural eco-system like grassland, wetland, and forest to understand the carbon flux over that
longer time period. This method has been used for, since the early, mid-1980’s and it’s been widely
used everywhere. The whole idea is, we have a sonic anemometer to measure 3-D wind speed; and in
the meantime, also you measure the gas concentration of CO 2 , water vapor, or methane next to the
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Impact of Changes in Barometric Pressure
on Landfill Methane Emissions
Liukang Xu
February 29, 2012
sonic. The whole idea is the air near the surface is not laminar flow – it is not always horizontal, but it is
up and down, up and down and we called this an Eddy,or air parcel, and that air parcel is sometimes
you’ll see a big air parcel and sometimes you have a, see an, smaller air parcel. The smaller air parcel,
that movement is much faster, we call it high frequency, and the big one is lower frequency. So, you use
that anemometer to measure the direction of the air parcel movement. At the same time you measure
that gas concentration in that air parcel and over the half hour or one hour you do averaging. You will
get how much your system is up-taking the gas or releasing the gas.
SLIDE 11 [08:40]:
Here it shows the equation is flux, or emission, is = ws, means averaging over that half hour or one hour.
The “w” is the vertical wind speed, you measure with the Sonic Anemometer, and “s” is the gas
concentration for CO 2 or for water vapor or for methane for other, any other gas – normally is millimole
per cubic meter(mmol m-3). The requirement for this Eddy Covariance Method, you need fast, and
normally people are using 10-Hz sampling rate for the wind speed and for the gas concentration and
also the gas analyzer needs to be very precise. The precision and accuracy need to be very high because
the concentration difference between the down-draft air parcel or up-draft air parcel, the difference is
very small and we want to resolve all this small difference.
SLIDE 12 [10:00]:
As I said earlier, this Eddy Covariance Method is being used everywhere since mid-1980’s, and they used
it for crop field, natural eco-system, and also suburban area, volcanic area, ocean. On this map it shows
over five hundred CO 2 flux stations running continuously using this Eddy Covariance Method; the
scientists tried to understand the CO 2 flux over various eco-systems.
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Impact of Changes in Barometric Pressure
on Landfill Methane Emissions
Liukang Xu
February 29, 2012
SLIDE 13 [10:47]:
This map shows the location of the Bluff Road Landfill in Lincoln.
SLIDE 14 [11:01]:
The red cross is our flux tower and, also, at the lower left corner, I have a one hundred meter as a ruler
to show the scale of this landfill. This landfill opened in 1988 and estimated closure will be in 2035.
And, we already have 6.1 million tons of waste in place. In that place, where we installed the tower, the
depth of the waste is 18 to 40 meters deep.
SLIDE 15 [11:56]:
The Eddy Covariance Method gives you that averaging emission, or average flux, over the footprint area
in the upper wind direction. OK, as I show in this slide, let’s say we’re assuming wind is from east, and
at the east side of our tower, I draw to two raindrops. This represents the footprint area so that Eddy
Covariance Method gives you that average emission over this footprint area. Now, the footprint size
depends on the stability of the air, the instrument height, and the roughness of the surface. As a rule of
thumb, the footprint area, the distance, is about a hundred times your instrument height. Let’s say you
mounted your instrument two meters to a tower, the footprint is up to two hundred meters in the
upper wind direction. Again, this footprint is dependent on the stability of the air. Let’s say in the
afternoon, the air is very unstable, the footprint, it will be much smaller, it could be like fifty times of
your instrument height and when the air became stable, the footprint will be much longer.
SLIDE 16 [13:45]:
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Impact of Changes in Barometric Pressure
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Liukang Xu
February 29, 2012
When the wind changing from east to north, and the footprint also changing to the northside of your
instrument tower.
SLIDE 17 [14:03]:
Again, if the wind changes to the west, the footprint also changes.
SLIDE 18 [14:16]:
You need a Sonic Anemometer and a gas analyzer to do that Eddy Covariance measurement for that
methane emission. Here, we show that Sonic Anemometer sitting on the middle on the tower and that
CO 2 and H 2 O analyzer is sitting at right side of that Sonic Anemometer and at the left side of the Sonic
Anemometer, we have a methane analyzer and we have/show the control box, data logging control box,
and also a solar panel. We don’t show, here in this picture, is that radio link. You know, we use a radio
link to transmit that data to the computer in my office.
SLIDE 19 [15:26]:
The major, the main advantage of this technique, it is a direct measurement, it can be automated, and
we set this thing up in early June of 2010, it being continuously running since then. It can do continuous
measurement as long as you’ve got the power and also no disturbance to that underlying surface. If
you use as a measure like a chamber based measurement, you will change, you are changing the
environment.
I want to make sure that all of us here know the difference between the two basic concept. The first
one is methane production. It is defined as the amount of methane produced inside the landfill per unit
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Impact of Changes in Barometric Pressure
on Landfill Methane Emissions
Liukang Xu
February 29, 2012
area per unit time. So this methane production, it depend on the amount of waste at the landfill, the
composition of the waste, and the age of the waste, and now, of course, the weather condition, the
temperature, the moisture from precipitation.
SLIDE 20 [16:56}]:
Another concept is the methane emission, which is the amount of methane escape from the landfill into
the atmosphere per unit area per unit time. Of course, this will depend on how much methane is
produced inside the landfill, and that, also minus the amount of the methane oxidized in the top
covered soil, minus the amount of methane recovered [if you have a recovery system to capture the
methane, either through burning it or using it for electricity], and also I will show here in our data, the
methane emission also depends on the rate of the barometric pressure change.
SLIDE 21 [17:56]:
Here, I plot the CO 2 emission versus the methane emission. The methane emission on the X- axis, and
CO 2 emission on the Y-axis. That red closed symbol represents the data we got from November and
December and the black symbol represents the data from June to October. The slope is different from
these two groups of data. For the wintertime data, the relationship between CO 2 emission and
methane emission is very tight and slope is 0.76; the summertime, the data is much scattered around
and the slope is higher. The reason for the two different slopes is because in the winter-time that
methane oxidation rate almost stops and, also, the soil respiration and also pretty much stopped
because in Nebraska the winter-time the soil is frozen. So, in the winter-time the methane emission and
the CO 2 emission is, more or less represents, the methane and the CO 2 produced inside the landfill,
which we measured the methane composition and the CO 2 composition from the gas- we extracted it
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Impact of Changes in Barometric Pressure
on Landfill Methane Emissions
Liukang Xu
February 29, 2012
from at the well and the ratio is exactly 0.76). In the summer-time, some of the methane produced
inside the landfill got oxidized and so the methane emission will be less than the methane produced
inside landfill, but CO 2 emission could be higher than the CO 2 produced because you have soil
respiration going on. From this data set, it gives us some kind of confidence and the validity and the
quality of our emission data with this Eddy Covariance technique.
SLIDE 22 [20:53]:
Here, we show the example of the methane concentration over the landfill, as we measured with the
methane analyzer, at the height of three meters above the surface; how fast the methane concentration
changing with the pressure changing; and this data set that we obtained on June 7, 2010, before 1:30
[1330 on the graph] the methane concentration is changing from like 2 ppm to almost 6 ppm. That’s
because of the turbulent nature of that air, like when you have a downdraft air parcel coming into the
surface; you’re bringing fresh air with lower methane concentration to your instrument. When you have
an up-draft air parcel moving through your instrument, you will see higher concentration of methane
from the landfill. That’s why you are seeing large variations of the methane concentration. But, when
the pressure increase from 96.9 kPa to 97.1 kPa and the response of the methane concentration in the
air is just changing dramatically from almost 6 ppm to 2 ppm, which is the background of methane
concentration in the atmosphere. See after 1:30 [1330 on the graph], the end of the methane
concentration is just flat; the high pressure coming in, you push a lot of fresh air into the landfill and
kind of block the methane diffusion to the air.
SLIDE 23 [23:27]:
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Impact of Changes in Barometric Pressure
on Landfill Methane Emissions
Liukang Xu
February 29, 2012
Now the methane concentration, high methane concentration will tell you, more or less, the higher
methane emission, but the relationship is not one to one. Here, we show the methane emission we
obtained in September, 2010, and on that left Y axis is a methane flux. The unit is µmol m-2 s-1. As I said,
this unit represents the average methane emission in the footprint area; and that Y axis on the right side
is the barometrical pressure; we show in this red line. From this data set, it’s very clear, you see, I use
that light yellow color shaded area when you have pressure increase. See, whenever we have a
pressure increase, the methane emission drops to below 5 µmol m-2 s-1.
SLIDE 24 [24:50]:
Now, whenever you have a pressure drop, the methane emission is enhanced significantly to over,
sometimes to over, 40 µmol m-2 s-1; and I highlight quite a few examples here in this data set.
SLIDE 25 [25:19]:
In this data set that we obtained in December, this phenomenon is even clearer. When you have a
pressure increase, sometimes, you almost stop that methane emission.
SLIDE 26 [25:43]:
And, whenever you have a pressure drop, you see a huge methane emission came out from the landfill,
almost a 100 µmol m-2 s-1.
SLIDE 27 [26:07]:
Now, we want to rule out any artifacts might cause the relationship pertaining to methane emission and
the barometrical pressure changing we observed from our data set; some people argue, may be due to
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Impact of Changes in Barometric Pressure
on Landfill Methane Emissions
Liukang Xu
February 29, 2012
the wind direction-shift changing, and we plotted this methane emission versus the wind direction, and
we do see some variation in that wind direction. In different wind direction you have say a wind, you
see a methane emission different rate, but we don’t see zero emission from one particular wind
direction, so we are confident about the data we saw and we showed in our previous slides.
SLIDES 28, 29 [27:08, 27:26]:
We also looked at barometrical pressure and see there is no change in Nebraska in the year 2007, 2008
and 2009; and in the bottom plot we saw three years of data set, and on the top plot we show half a
year’s data, that we obtained from the landfill and we don’t see any significant difference between the
second half year of our experiment and also compared with previous years. We also looked at pressure
changing and seasonal pressure changing in the West Coast and East Coast.
SLIDE 30 [28:08]:
This data set that we got from the AmeriFlux site, and they have a continuous barometrical pressure
data; one is from Maine and another one is from California; the red one is from Mead in Nebraska which
is, like, forty miles north of our landfill. All three sites show that pretty much similar amplitude and the
frequency, and we did a spectra analysis show the peak and power of the spectra distribution at
different frequencies – they are all very similar.
SLIDE 31 [28:57]:
We, also, analyze the power spectrum for that barometrical pressure and the methane data we
obtained from our site; and, here again, show the pressure, the peak of the pressure variation usually
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Impact of Changes in Barometric Pressure
on Landfill Methane Emissions
Liukang Xu
February 29, 2012
about 5.6 days, and methane is like 4 days for methane, and for the pressure, you know, we have a
daily cycle which is twenty-four hour, and half-day cycle twelve hours, it’s also clear.
SLIDE 32 [29:47]:
From this plot, this analysis we can see that the pressure variation and the methane variation, methane
emission and variation follow each other. We just showed that methane emission from the landfill is
closely correlated with that pressure changing. When you have a, when you see the pressure increase
and the emission is suppressed, and when you have a pressure drops the methane emission is
enhanced. Here, we show that from the whole duration of our half-year’s field experiment, the black
dots is half hourly methane emission; the blue line we averaged the daily emission to one day mean, OK,
and the black line is the six day mean data, and the red line is ten day mean data. So, in the warm
season you need a six-day continuous measurement to average out that effect of the pressure variation
on the methane emission. You need to do it continuously. In the cold season, in December or
November, you need ten days averaging continuous measurement to get the good emission data. From
this data, we also see in the wintertime, the emission is slightly higher than in the summertime; this not
necessarily mean the production of methane in the winter-time is higher than in the summertime, but it
did tell us the oxidation rate in the wintertime is much smaller than in the summertime, that is why the
emission rate is higher in the wintertime. Another point I want to make is when you average it over six
day or ten days, you’ve got a pretty much flat emission. This tell you the methane hold inside the
landfill during the pressure rising phase is not lost, is not oxidized; it’s just the methane will flush out
when the pressure drops.
SLIDE 33 [32:59]:
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Impact of Changes in Barometric Pressure
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Liukang Xu
February 29, 2012
This methane emission we saw is a very closely related to the pressure changing. This phenomenon is
not totally new; in 1990 a paper published in Nature, some people saw, from the lake, they observed
that methane bubble released and more bubble released from the lake when you have lower pressure;
and then one year later, another paper published in Nature, this said, also said that this “phenomenon
has been known to the mining engineers in the UK for more than 250 years”, and some of the disasters
and explosions in mining has been related to the lower pressure so they have installed a pressure gauge
at that site. If the pressure drops too fast, that operation needs to be suspended even if you do have a
very modern ventilation system.
SLIDE 34 [34:30]:
More modern data recently also shows that the methane emission from wetland or from peatland has
been related to the pressure drops.
SLIDE 35 [34:55]:
The implication from our results, the next couple of slides I will discuss this – the implication. We, the
current method for quantifying the methane emission from landfill is: Plume Tracer, Mass Balance, or
Chamber Based Measurement. Here, I show just an example of how the Plume Tracer Method works.
As we release the tracer at the landfill and then at a certain distance in a downwind direction, they
measure the concentration of this tracer and, in the meantime, also measure the concentration of the
methane. And, you use the equation at the bottom of the slides to get methane emission from the
landfill – Qt is the total amount of a tracer released from a landfill; Cm is the methane concentration
measured in a downwind direction; and the Ct is a tracer concentration measured in a downwind
direction.
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Impact of Changes in Barometric Pressure
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Liukang Xu
February 29, 2012
SLIDE 36 [36:23]:
Now my question is, “You use tracer plume method or mass balance method to do the measurement, is
during the time when the pressure increase or during the time when the pressure decrease?” – you will
have a huge different in your measured emission rate. Here, we just show an example, if you measured
on the date of December 2nd, or no, December 21st, you will pretty much don’t see any methane
released from the landfill. But a few days earlier, on December 15th, you will see huge methane released
from that landfill. So, if you estimate any total based on this kind of measurement, you will definitely
see a large variation in your estimated number.
SLIDE 37 [37:37]:
Another implication from our results is, as probably all of you know, the government has some kind of
regulation required to monitor the surface methane concentration over a period of time, and from our
results, we would recommend that surfaces concentration measurement must be made during the
pressure falling phase, “especially if there is a requirement to issue a hazard warning,” as pointed out by
A. Young and also in UK, and this is because the lower concentration you measured during the pressure
rising phase doesn’t necessarily mean that you don’t have a leak, you don’t have any issue here.
SLIDE 38 [38:43]:
The next step we want to do is try to upscale from that Eddy Covariance Methane Emission data to the
whole landfill, so you get the total landfill emission. This total number, that local government or EPA,
they are interested, rather than the emission rate from the Eddy Covariance. Another thing we want to
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Impact of Changes in Barometric Pressure
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Liukang Xu
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do is try to do more Eddy Covariance Methane emission measurement at another landfill to see our
data, our results, still hold.
SLIDE 39 [39:31]:
In conclusion, from our study, the landfill methane emissions are strongly correlated with the changing
in barometric pressure; and the increased pressure suppresses emission; and decreased pressure will
enhance emission. And it’s also essential to have a continuous measurement in order to have a good
estimate and the total methane emission over the season. Another implication is a landfill surface
concentration measurement must be made during the pressure falling phase. If you do the
measurement during the pressure rising phase, the data is almost meaningless.
SLIDE 40 [40:33]:
Okay, I’m leaving some time for questions. Ashlee, do we have any questions?
Moderator:
All right. Thank you, Liukang. I have passed most of our questions on to our panelists to be answered.
So, hopefully, everyone’s questions have been taken care of. However, if they haven’t, just stick around
and one of us will get you an answer very soon. And, feel free to keep submitting your questions
because we’ll stick around until all of them have been answered. If you’d like to continue your
conversation with our panelists or Liukang, you can do so offline via email or phone. I’d also like to
inform you that an on demand replay of this presentation will be posted to our website fairly soon. Just
watch your email or visit www.licor.com/env/webinars for more information about that. So thank you
for joining us today and we hope to see you at our next webinar.
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