Archive for April, 2020

On wind, CO2 and other gases (2/3)

April 26, 2020

In this 2nd part we will taker a deeper look into CO2 variations, wind speed, ground ozone and solar irradiance. I will settle down on the 11 days period from 14 to 24 April 2020 inclusive. The data are fed into STATISTICA, and graphs are made in that software.


2. CO2 and wind speed over the 11 days, and a zoom on two days

This plot shows the dampening of daily CO2 peaks during the 3 day period where wind speed was higher 24 hours around: the CO2 peaks plunge from about 540 to less than 430 ppm, practically by one fifth! This windy period stops the 23th April and the 24th we are back to a 520 ppm morning peak. The 3 days low period covers Monday, Tuesday and Wednesday, i.e. days witch despite lockdown have certainly more traffic than what happens during the weekends (Saturday, Sunday: 18 & 19 April)

Let us take a look at two days, the Friday 17th April belonging to the low-wind period, and the Monday 20th April where the wind blows strong.

I choose the same scales on both figures, which allows a better visual appreciation: compared to the upper graph, CO2 levels seem practically flat during the windy period.

Conclusion #1: CO2 levels at Diekirch are mostly lowered by air movements, which dilute the CO2 concentration through a higher mixing of the near-ground air.

Attention: this is a preliminary conclusion; we know that photosynthesis is the big CO2 killer, and uses is as the building blocks for making plant matter. So we must also look at solar activity (irradiance, energy per day ….) to check if our CO2 slump is not simply the result of a stronger photosynthesis.


3. CO2, ground ozone and solar irradiance

But let us look first how another gas that we measure at meteoLCD varies during the same period: ground O3. The next combined graph shows how CO2 and O3 vary together, and how CO2 and solar irradiance change.

3.1 First the O3 problem:

During the “non-wind” periods O3 levels plunge to near-zero at the morning hours, whereas they remain relatively high during the windy days. Exactly the opposite what we see with CO2! The 2 turquoise lines show CO2 minima and O3 maxima happen at the same time during late-afternoon.

Now we know that nightly O3-patterns differ markedly between city and rural locations. In a city with its ongoing 24/24 traffic, O3 destroying emissions of NO remain efficient, and, in the abscence of UVB radiation which creates O3, rapidly lowers O3 concentration. The opposite happens at rural stations: no night traffic, no NO emissions, no hugely important destruction of O3: especially when night temperatures remain high, O3 minimum levels do not fall back to say 10 ug/m3, but stay at 60-80 ug/m3.

Let us check this using the measurements made at Beckerich, a semi-rural village similar to Diekirch regarding traffic: 2 peaksper day of in- and outgoing traffic from the foreigners working in Luxembourg , and a moderate traffic level during the rest of the day. This is nicely shown in the following picture:

The upper plot shows the O3 concentration, and the lower the NO2, which we will use as a proxy for NO. The two red vertical line show the morning NO2 peaks and the corresponding O3 lows. If one looks carefully, two NO2 peaks per day can be seen. The highlighted section corresponds to the windy days (remember that these are working days!): NO2 levels remain very low, and so do not bring down O3 concentration to near zero!

Conclusion #2: NO2 levels respond to wind speed as does CO2; more wind means more dilution and lower levels. O3 concentrations do not! Not all atmospheric gases are impacted by higher wind speed in the same manner!


3.2. And now solar irradiance and temperature in more detail:

Can we see the influence of solar irradiance (and air temperature) during low-wind days? Intuitively one would expect stronger air movements by convection when solar irradiance (and air temperature) is higher. So the morning CO2 minima should be lower during sunnier and warmer days.

First a plot showing CO2, solar iarradiance and air temperature for the two “wind-poor” days of 15th and 23th April
Clearly solar irradiance and air temperature is higher on the second day: so this 23th April air convection movements as well as photosynthesis will both be higher.  To have a clearer picture, let us retain only CO2 and air temperature:

The CO2 minimum is 8 ppm lower on the warmer and sunnier day.We can not dissociate the two CO2 lowering causes, convection and photo-synthesis; suffice to say that the lowering of  8 ppm has to be compared with the peaks which are more than 100 ppm lower during windy compared to wind-still days… a difference of one magnitude!

Conclusion #3: The huge CO2 lowering effect during windy days is caused by increased air movements. The variations caused by photosynthesis and air convection are much smaller.


(to be continued with 3rd and last part)

On wind, CO2 and other gases (1/3)

April 24, 2020

wind (link to image)

1. Introduction

meteoLCD is one of the few stations that publish CO2 measurements at near-ground level; our readings give the real situation as it is. If you look at the CO2 plots (here), you may be surprised by the often huge daily swings in concentration, when the media usually suggest a smooth and continuous rise. BTW one should say “mixing ratio”, but “concentration” is so much easier on the mind…

One of the main factor influencing the CO2 levels is wind speed: no wind means no turbulent mixing of the boundary layer, and especially at the cool morning hours, CO2 will remain trapped by the inversion and levels reach high values. During the day, when the sun warms the air, convection springs into action and this will dilute the CO2 concentration. Now, add some more or less heavy wind movements, and that dilution will reach “extreme” levels. The concentration begins to be comparable with the numbers published by stations located at the beach-front, on small islands or on top of a high volcano, as is the case for the famous Mauna Loa station. But even Mauna Loa must watch its steps: from time to time the volcanoes belch out a CO2 plume, and this moments must be “edited out” of the data series. Other continental stations keep only the measurements done in the afternoon, to get what is called “the background level”.

I published a very long time ago (2009) a paper with the late Ernst-Georg Beck on how to calculate that background if one has both the wind-speed data and the CO2 mixing ratio. Beck was a specialist on vintage CO2 measurements done with chemical methods, and so we tried to find a possible background out from these historic measurements. You may look at the paper (published by Springer) here. In our TRENDS section I redo this exercise every year, and this is the situation for 2019:

The number 411 ppmV represents the horizontal asymptote and is practically the same as the Mauna Loa value for 2019 (411.4), so this might be a lucky year!

The last days, we had sunny weather, and several days with high wind speed, than 3 days with poor wind, and again a couple of more windy days. Look how the CO2 concentration was influenced by this wind pattern (the graph is from today, Friday 24th April 2020):


Do you see the difference?

Well, in the next part which I try to write during the weekend, we will look more into the details, and see how other atmospheric gases like ozone and NO2 behave during that same period.


(to be continued)


Lockdown and no PM improvement! (2/2)

April 18, 2020

I took the time today to look at the 4 PM measuring stations of Luxembourg, and to check if these stations that all use the same equipment (Horiba  APDA371 ) show an improvement in PM 2.5 concentration between the periods 14-March to 12-April in 2019 and 2020. Here a map of tiny Luxembourg (distance from South to North is about 86 km) with the 4 official stations and our meteoLCD facility at Diekirch:


The 3 stations at Place Churchill, Bonnevoie and Esch are town stations, with usually heavy traffic around. Beidweiler is a rural station and Diekirch is best seen as semi-rural.

The official data can be found here and ours at meteoLCD here.

I downloaded all data from the discomaps site; the labels of the 4 official stations are:

ESCH                LU_0102A

The conclusion is practically the same as in the first part of this comment. The following picture says it all: there is no distinctive fingerprint of the lockdown to be seen. The averages are computed from the published hourly readings.


One could eventually see a more smooth pattern at Churchill, but the difference between the averages is small, and note that all these averages are little. The rural Beidweiler and the town station at Esch do really not behave well, as they have increased PM2.5 levels during the lockdown (not much for Beidweiler, but nearly +50% in Esch).

The EPA’s revised standard from 2012 are 35 ug/m3 for the daily average, and all 4 stations are well below this. The annual average should be lower than 12 ug/m3, which seems quite extreme, as wind blowing over dry soil can produce quite spectacular amount of PM2.5 and PM10 (and let’s not speak of wood burning). The paper here for instance gives a number of 12.2 mg/m2 blown away as PM2.5 when wind at 8m/s blows over uncrushed soil: so every m2 of soil surface would expel 12200 ug of PM 2.5 in these windy conditions! Even with a 100 fold dilution does this still amount to concentration of 12 ug/m3.

Lockdown and no PM improvement! (1/2)

April 13, 2020


Luxembourg went into economic lock-down (well “pseudo-lockdown” would be more appropriate) the 14th March 2020 with schools, most industries, shops, restaurants, sports activities etc. stopped and people asked not to leave home except for very important, exceptional reasons. The road traffic diminished drastically; here at meteoLCD we are used to heavy morning and evening traffic spikes when many foreigners who work in Luxembourg enter the country in the morning and leave in the late afternoon. The roads have become very empty…and all this should show up in the air quality parameters….but surprise, it doesn’t !

This has been observed and commented on other places. In very polluted large cities, NO2 levels have been seen falling, but not everywhere. Read this recent article in Nature where atmospheric scientist Dan Goldberg from Argonne National Laboratory is cited with “I haven’t seen any statistically significant changes in air pollution in most US cities, which is contrary to the claims in some media articles”.  The German FOCUS online of today (13-April-20) has an article from Dipl. Ing. Martin Schraag titled “Kaum Verkehr…trotzdem Stickoxide Spitzenwerte: Corona entlarvt Fahrverbote als sinnlos”.

So its time to look at the “real” numbers measured by meteoLCD and by our usual reference station of Beidweiler; we measure fine particles with an Airvisual Pro instrument from iQAir, Beidweiler uses an Horiba (you might re-read this article here for more details).

I choose the period from 14th March to 12 April 2020, which corresponds practically to the start of the lock-down period (which started definitively the 16th); we will compare with the same period from the previous year.

The Beidweiler data are fetched from the discomap EU database, which is a bit tricky to use. Suffice to say that Beidweiler is the Luxembourg station STA-LU0105A; I leave the pleasure to fetch the correct data to the Sherlockians of my readers! The 2020 meteoLCD data are fetched from the Airvisual cloud.

Here a table showing what happened to the fine particle concentrations during these two periods; the numbers correspond to the averages over the period:


Clearly not much to see here: the Beidweiler PM2.5 concentration increased slightly with better air, and the meteoLCD values decreased about the same amount. These changes are so small that they are well below the accuracy level of both instruments; so there is only one conclusion to draw: at these two stations, which are typical for rural/semi-rural locations, the traffic lock-down does not leave any visible trace!

The AQI number is the US-AQI as defined by EPA; it would be foolish to conclude from the small decrease that air pollution in Diekirch became less!

Here two graphs showing the Beidweiler and meteoLCD data for the two periods:



Now, comparing raw PM readings is a bit rude; we know that meteorological parameters play a very big role. Suffice to say that the mean temperature was about the same (9.11, and 9.64), wind velocity also (1.98, 1.74). UVB radiation was a bit higher in 2020 (2019: 199, 2020: 248 mMED/h), but contrary to what one would expect, ground Ozone levels were lower (2019: 93, 2020: 48 ug/m3). So if the traffic lock-down has eventually left a small finger-print, the O3 level would go in the expected direction.


Do you remember the sometimes ugly discussions last year about the lethal danger of PM’s, and that Diesel cars should be banned as soon as possible; but always ignoring that lean injection petrol engines emit about the same amount of NOx and PM’s, and still ignoring that the “green” -hyped wood burning is one of the major emitters of fine particles. In Germany the opposition to the very efficient Diesel cars reached religious fanaticism… and what do we see know, when Covid-19 has forced us to make a “super-experiment”:  PM 2.5 levels remain as they were!

(to be continued)



COVID-19 Luxembourg: an animation of the Gompertz fit (4/x)

April 11, 2020

I have added an animated GIF to the meteoLCD site showing the evolution of the total infected number for Luxembourg, together with a Gompertz fit made the current day and a visual indication of the uncertainty range (the yellow rectangle):


The Gompertz equation is Total = a*exp(-b*exp(-c*Day)); to make a consistent non-linear fit (using Statistica with a Levenberg-Marquardt algorithm) the initial values of the 3 parameters have been kept constant: a=2000, b=0.10, c= 0.05

Starting 24-March-20 the fit and the parameters are statistically significant (at the 95% level, R2 is always >0.99). To make a correct animation, one has to be careful that the general layout of the graphs does not change from plot to plot (same text except date, same scale of axis, etc.). I used the free online animated GIF maker at, which is quite handy. The Gif maker allows to change the time delay individually for every picture, which is quite handy (I did not see this feature in the first animations made, but use it now…). The animation is built upon the graphs of every second day.

Click here to access the animated GIF!