Computing HITRAN data, basic global temperature increase for doubling CO2 is limited to 0.16K-0.20K

Guest contribution by Frans van den Beemt

Full version of an earlier summary

Long read.

**Abstract****
**We analyzed CO2 absorption and emission of infrared radiation and calculated the upper limit of a possible temperature increase at the earth’s surface, including the effect of average annual cloud cover. We used HITRAN spectral data and the general laws of physics and quantum mechanics for the calculations. We found 1.33 Wm

^{-2}additional absorption for doubling CO

_{2}. Assuming that 40-50% will be emitted into space and 50-60% contributes to a surface temperature increase, we find a worst case upper limit of 0.16K-0.20K. We assess that the assumptions in IPCC report 2014 of 3.8Wm

^{-2}and 1K increase respectively are overestimated.

*Samenvatting*

*We analyseerden de CO2-absorptie en emissie van infraroodstraling en berekenden de bovengrens van een mogelijke temperatuurstijging aan het aardoppervlak, inclusief het effect van de gemiddelde jaarlijkse bewolking. We hebben berekeningen gemaakt met behulp van de HITRAN spectrale gegevens en de algemene wetten van de natuurkunde en de kwantummechanica. We vonden 1,33 Wm ^{-2} extra absorptie voor het verdubbelen van CO2. Ervan uitgaande dat 40-50% daarvan wordt uitgestraald naar de ruimte en dat 50-60% bijdraagt aan een stijging van de oppervlaktetemperatuur, vinden we een bovengrens van 0,16K-0,20K. We tonen hiermee aan dat de aannames in het IPCC-rapport 2014 van respectievelijk 3,8 Wm^{-2} en 1K stijgen, te hoog zijn ingeschat.*

**Introduction
**Infrared (IR) active gasses (like H

_{2}O, CH

_{4}, CO

_{2}) in our atmosphere interact with IR emissions of the Earth’s surface. In this article we focus on the physics of this interaction for Carbon Dioxide (CO

_{2}) only. CO

_{2}molecules absorb IR radiation from the surface and this energy is transferred to the surrounding molecules by collisions, which propagate it further into the never resting atmosphere. CO

_{2}molecules also have their own spontaneous and induced IR emission. Part of the IR emissions from the surface as well as from the atmosphere and clouds will be emitted into space, cooling the Earth. The net absorbed radiation in the Earth’s atmosphere controls its temperature. The question is how much an increase in CO

_{2}concentration affects the atmosphere temperature at the surface. This temperature depends on several physical processes: evaporation, condensation and ice crystal formation, precipitation, cloud formation, aerosols, convection, wind, gravitation, Earth’s rotation and the radiation properties of its IR gasses.

Commonly numeric methods are used to compute the relationship between CO_{2} concentration and atmospheric temperature, based on well formulated radiation transport equations through the atmosphere. After each calculation cycle the results are corrected for other physical processes. Here we took a different and overarching approach. Firstly, we calculated an upper limit for absorption of energy (additional absorbed energy) by CO_{2} in the atmosphere for a doubling of the CO_{2} concentration. Then we used this additional energy to compute a best guess of a temperature rise, taking into consideration a global yearly average cloud cover as a result of convection and advection processes. This shields incoming radiation of the sun as well as outgoing IR radiation from the surface and atmosphere. The IR emissions of the clouds are assumed to contribute to emissions into space as well as to emissions towards the surface. We did not use the radiation transport equations because we computed the maximum possible absorption by CO_{2} molecules, which requires no specific details of the radiation transport.

**Methods
**We focus on the troposphere, where virtually all radiation interactions occurs. Also collisions between molecules here are fast enough to nullify additional spontaneous emissions and ensure transfer of absorbed energy to all molecules of the atmosphere, mainly to N

_{2}and O

_{2}. We use the theory and formulas derived from Beer–Lambert law, Kirchhoff’s law, Planck’s law, Stefan–Boltzmann law and Einstein coefficients for emission and absorption.

**Calculations and Results**

We calculate the absorption of infrared radiation by CO_{2} molecules in the atmosphere under global mean conditions, initially ignoring effects of H_{2}O molecules. We consider a one dimensional system perpendicular to the Earth’s surface and assume the Earth’s surface emitting black body radiation upwards. We limit ourselves to the 15µm band the main absorption band of CO_{2}. At first we disregard the temperature and pressure gradients, using average values at the Earth’s surface.

Using Planck’s law for black body radiation, the formula for radiation intensity I is:

(1) dI/dϑ = I_{ϑ} = 2πhϑ / λ^{2} * 1/ {exp(hϑ/kT) – 1}

At frequency ϑ=15µm,

λ=c/ ϑ, c=299792458 m/s light velocity in vacuum,

T=300K , Planck constant h= 6.6*10^{-34} J s ,

Boltzmann constant k= 1.38*10^{-23} J K ;

with I is radiation intensity we calculate dI/dϑ(15µm, 300K) = 1.7*10^{-11} J m^{-2}. For the second important CO_{2} frequency at 4.3µm we calculate dI/dϑ(4,3µm, 300K)= 3.15*10^{-13} J m^{-2} or only 2% of the value for 15µm, that’s why we will focus further on the most important spectral band at 15µm.

References for formula (1): [R.Kronig 1966; page 1012 formula (9)][i], [A.Yariv 1968;page 87 formula (5.3-4)][ii], [R.Goody 1989; formula (2.37)][iii] and [H. Harde 2013;page 7 formula (50 and 51)][iv]

Absorption per unit traveled:

(2) d I_{ϑ} /dx = -λ^{2}/8π*A*g(ϑ)*N_{co2}(j)*I_{ϑ} where I_{ϑ} is given by (1)

x is radiation path length in meters (or height above Earth’s surface)

A=1,35 s^{-1} : Einstein coefficient of spontaneous emission

g(ϑ) : normalized line shape function with natural line width Δϑ(1 atm)= 4.2*10^{9} Hz

N_{co2}(j) or N(j): population CO_{2} molecules for rotational quantum number j

References for formula (2): [A.Yariv 1968; page 210 formula (13.3-15)]^{ii}, [R.Goody 1989; formula (2.54)]^{iii} and [H. Harde 2013; page 9 formula (55) and page 5 formula (32)]^{iv}

References for rotational quantum number j: [R.Kronig 1966; page 570 a.f.]^{i}, [W.Witteman 1986;section 2.3][v] and [R.Goody 1989; section 3]^{iii}

(3) N_{co2}(j) = N_{co2} * (2hcB/kT)* (2j+1)*exp{-hcB/kT*j(j+1)}

B: rotational constant =0,39 cm^{-1}

For j=20 we get: N_{co2}(20)= 5,64.10^{14}

References for formula (3): [W.Witteman 1986; page 17 formula (2.20)]^{v}, and [Laurendeau 2005;Page 180 Formula 9.37][vi]

References for rotational constant B: [W.Witteman 1986; Page 23 tables]^{v}, and [Rothman 2004; HITRAN 2004 database][vii]

The total absorption over the traveled distance x and over all frequencies ϑ is computed by integration of I_{ϑ}.d ϑ from minus infinity to plus infinity, resulting in:

-λ^{2}/8π*A*N_{co2}(j)* I_{ϑ}

where integration of g(ϑ).dϑ from minus infinity to plus infinity = 0 and I_{ϑ} is constant over g(ϑ) for black body radiation.

At pressure broadening normalized line shape function becomes:

(4) g(ϑ) = ½*π* abs{Δϑ}/{ (ϑ – ϑ0)^2 + ( Δϑ/2)^2 }

References for formula (4): [A.Yariv 1968;page 211 formula (13.3-19)]^{ii}, [W.Witteman 1986; page 12 formula (2.8)]^{v}, [R.Goody 1989; section 3]^{iii} and [H. Harde 2013;page 3 formula (7) and page 6 formula (39)]^{iv}

Abs{Δϑ} = I ϑ_{x} – ϑ_{0} I the standard deviation (half value) is reached at y where ϑ_{y} is the frequency where g(ϑ_{y}) = ½*g(ϑ_{0}) , see Figure 1.

In the x direction the radiation travels over a path L through the atmosphere.

Integration of (2) over height x from x = 0 to x = L provides a radiation intensity at x=L:

(5) I_{ϑ} (L) = I_{ϑ} (x=0)* exp{ -L*λ^{2}/8π*A*g(ϑ)*N_{co2}(j) }

The remaining radiation intensity after absorption depends on the value of the exponent { -L*λ^{2}/8π*A*g(ϑ)*N_{co2}(j) }

If we chose { L*λ^{2}/8π*A*g(ϑ)*N_{co2}(j) } = 1 the value of the exponent becomes exp{ -1) = 1/e (with e =~ 2,71). At a distance x= L there is 1/e left of the original intensity I_{ϑ} (at x=0) at a certain value of ϑ . This is already less than the standard deviation (half value). Three times the standard deviation equals a decrease of the original intensity I_{ϑ} (at x=0) of 95%. Consequently if the computed traveled distance is L, for which the value of the exponent = -1 then at a distance 3L the radiation will be absorbed by 95% or more.

_{2}, the Q-branch, around 15µm (wave number 667 cm-1) is already fully absorbed in the first tens of meters (see Figure 2) [H. Harde 2013]

^{ iv}. We zoom in on the side lobes or side branches, consisting of many overlapping spectral lines. In this case, pressure broadening of spectral lines are a consequence of optical collisions between CO

_{2}molecules that stimulate and activate absorption in the rotational bands of CO

_{2}. With pressure line broadening, extra absorption takes place between the diverse spectral lines that come closer together. The larger the overlap, the more the absorption.

To get an impression of the absorption in the side lobes, for the P-branch we consider the adjacent spectral lines for j = 20 and j = 22. Note that the R-branch produces similar results. The central frequencies of the relevant spectral line belonging to each value of j originate from the HITRAN database [Rothman 2004]^{vii}, a table of values measured in laboratories. The intersection at which the two wave functions (spectral lines) overlap is called x with frequency ϑ_{x} and probability distribution function g_{x} (ϑ_{x}).

The HITRAN database allots the line frequencies for each rotational quantum number j of the P and R branch of the CO_{2} 15 µm V_{2} rotation-vibrations spectrum. For example j=20 and j=22 we find: P(20) = 651.94 cm-1 and P(22) = 650.41 cm^{-1} and P(20)-P(22) = 1.53 cm^{-1} or 4.59*10^{10} Hz. The absolute value of the frequency band between the central frequency ϑ_{0} of each line till the intersection point ϑ_{x} then amounts to: I ϑ_{x} – ϑ_{0} I = ½*4.59 * 10^{10 }Hz.

With (4) we calculate g_{x}(ϑ)=9.12*10^{-13} at the overlap or crossing point x between these two lines P(20) and P(22) (see Figure 3). g(ϑ) get its value of 9,12.10^-13 at point x that lies at a distance (frequency band) of abs{ϑx – ϑ0} away from the center ϑ0 of g(ϑ).

With (5) and { -L*λ^{2}/8π*A*g(ϑ)*N_{co2}(j) } =-1 we find L=160m. We have now absorption for P(20) as well as for P(22) where these lines overlap. For each line we will have >=50% absorption within L=½*160=80m. This means that a fraction >=95% of the radiation is absorbed within L=3*80=240m; three times as far from the center ϑ0 of g(ϑ)

We determine for which value of j more than 95% of the radiation is absorbed over a distance of 3 km. At this distance the absorption decreases with roughly a factor 2 (Table 5) due to decreasing pressure and temperature with altitude. The path length for more than 95% absorption will then increase with this same factor 2 up to 6km. We find that for side-lobs with j<=46 more than 95% of the infrared radiation originating from the Earth’s surface will be absorbed in the troposphere.

For the increase in absorption in the troposphere for spectral lines with J>=48 we assume that the value g(ϑ_{x}) for which the argument of the exponent becomes -1 in combination with a characteristic height of L=1 km (so that 3L=3km) provide us the full (100%) absorption frequency band ʋx – ʋ0. The results are listed in the next four tables 1a and 1b and 2a and 2b. The absorption percentage is calculated as the full absorption band around a spectral line center for a certain j number divided by half of the whole band taken as the band between the two centers for line J and line J+1. The weighted absorption percentage is calculated as (ʋ_{x} – ʋ_{0}) * (percentage absorption).

The complete CO_{2} 15 µm V_{2} vibration band has a central part with J<=44 that fully absorbs LWIR in the Troposphere and a part for J>=46 with less absorption in the far side wings P and R. With (1) we calculate the absorption, using an averaged absorption over the far side wings, with from data the HITRAN database 2004 to determine the frequency band (and wavenumbers). The center line is 667 cm^{-1}. From the center line to the far wings we find P(46)=632 cm^{-1} and R(46)=705 cm^{-1}. For the far side wings with j=72 we find P(72)=614cm^{-1} and R(72)=726cm^{-1}. These bandwidths are common for the far side wings P and R of CO_{2} 15µm (see Figure 2) in use to determine the additional absorption at doubling CO_{2} concentration in our atmosphere. The additional absorption and as a derivative thereof the temperature increase at the surface is shown in Table 3.

**Surface temperature increase**:

For the temperature increase at the surface (ΔT_{s}) we use the following calculation, assuming a yearly and global mean situation where all dynamics are averaged.

For a more realistic picture we introduce the cloud cover factor α (or cloudiness factor) because of its direct effect on the incoming and outgoing radiation. Furthermore we ignore any effect of water vapor. See the formula and results in Table 4. For the cloudiness factor we use the international accepted value of 0,62 (62%) as a global and yearly average [Kiehl, 1997, Page 200][viii].

P(total emission to space) = P(clear sky emission of surface to space) + P(emission to space from cloud tops) – P(clear sky under the assumption half of Ph is lost to space).

P(emission to space from upper side clouds) is the emission at global average cloud cover approximately at 5km height and at 250K and for simplicity the value is taken as half of the emission from the surface at 300K.

**Assumption
**In our yearly and global average situation via convection and radiation half of P

_{h}and P

_{v}is assumed to enter space and half is assumed to cause a temperature increase at the surface (ΔT

_{s}). To get an impression how this affects the resulting temperature increase we calculate the results without these assumptions. So all P

_{h}and P

_{v}would contribute to a temperature increase at the surface we get the following results: ΔT

_{s}=0.60 for α=0 and ΔT

_{s}=0.32 for α=0.62.

At much higher CO_{2} concentrations than 600ppm the percentage absorption (as used in Table 3) approaches 100% for the P and R branch. At 100% for both side wings assuming proportionality we calculate as in Table 3 an additional absorption of 9 W m^{-2} and a temperature increase of 0.42K at the surface, which sets the limit for possible temperature increase for rising CO_{2}.

Variation of the cloud cover has a certain effect on ΔT_{s}: for α=0.50 we find upper limits for ΔT_{s}=0.20 K and for α=0 clear sky ΔT_{s}=0.30K. The actual increase of the temperature ΔTs will be lower.

Two examples that underpin our upper level calculation approach are:

- The absorption per unit traveled is proportional to the population CO
_{2}molecules for rotational quantum number j : N(j) see Formula (2). In reality the extra absorbed P_{v }decreases more rapidly with height than in the upper limit calculation above ( 1atm and 300K at all heights above surface) and as a result ΔT_{s}will be lower than calculated here. For the first 5 km we provide some figures about height above surface, pressure and temperature and the with height decreasing factor for the number of molecules N(j). We have used this factor 2 while chosing an characteristic height above the surface of L=1 km in order to calculate the absorption in the far wings, see text above Table 1a.

_{2}O vapor to calculate the maximum absorption by CO_{2}Water spectral lines show overlap with CO_{2}lines in the region of 15µm. In reality this overlap will decrease the real absorption, attributed to CO_{2}.

**Conclusion**

We present a straight forward calculation method, which results in maximum values for extra absorption by CO_{2} 667 cm-1 (15µm) for a CO_{2} concentration increase of choice.

At CO_{2} doubling from 300ppm to 600pppm and 62% cloudiness we found an increase of absorbed energy with a maximum of 1,33W m^{-2}. Due to convection processes that sets the temperature profile and laps-rate and due to symmetry and random direction of spontaneous emissions half of this: 0,67W m^{-2} would provide an increase of the surface temperature. The calculated maximum temperature increase of 0.16K appears negligible in respect of the complexity of the atmosphere and the temperature differences over the globe.

[H. Harde 2013]^{iv} found 2.6W m^{-2} and 0.3K (at clear sky and T_{s}=288K and water vapour content of 1.46% and CO_{2} doubling from 380ppm to 760ppm, cloudiness of 50% at 5km height), [H. Hug 2012][ix] found 0.2K (for CO_{2} doubling from 200ppm to 400ppm). The IPCC AR5 report of 2014 states that a double CO_{2} concentration provides 3.8W m^{-2} radiation energy that warms the air near the surface about 1K, without climate feedbacks. Our results do not support this notion.

Calculation spreadsheet available (soon) on request.

**About Frans van den Beemt**

*Frans obtained his MSc physics in June 1973 at the University of Technology, Eindhoven, The Netherlands and his PhD in Science Studies, June 2000, University of Leiden, The Netherlands*

*He held positions as Teaching Assistant, University of Technology, Eindhoven, The Netherlands, then as Research Fellow, Department of Experimental Nuclear Physics, University of Technology, Eindhoven, The Netherlands. Next he was teacher in Physics and Mathematics, Eckhart College, Eindhoven, The Netherlands, System Engineer, Machines & System Group Holec, Ridderkerk, The Netherlands and Program Director, Technology Foundation STW, Utrecht, The Netherlands He is founder of consulting firm: VdBeemt 2G Advies and founder of European academia consulting firm: HandsonGrants. He authored numurous publications and performed many specialized functions.*

**Notes and references**

[i] R. Kronig, Leerboek der Natuurkunde Scheltema & Holkema NV Amsterdam

[ii] Amnon Yariv Quantum Electronics, California Institute of Technology, book second edition 1968

[iii] R. M. Goody and Y. L. Yung, Radiation: Theoretical Basis, Oxford University Press, Oxford, UK, 1989.

[iv] Herman Harde Radiation and Heat Transfer in the Atmosphere: A Comprehensive Approach on a Molecular Basis, Hindawi —Publishing Corporation International Journal of Atmospheric Sciences, Volume 2013, Article ID 503727, 26 pages (2013) http://dx.doi.org/10.1155/2013/5037

[v] W.J. Witteman , “The CO2 Laser” December 1986 Springer Series in Optical Sciences Springer-Verlag

[vi] Normand M. Laurendeau, Statistical Thermodynamics Fundamentals and Applications, book Cambridge University Press 2005

[vii] Rothman, L. S. et al, (30 authors), J. Quant. Spectrosc. Rad. Trans. 96 139-204 (2005), ‘The HITRAN 2004 molecular spectroscopic database’

[viii] J.T. Kiehl and K.E. Trenberth, Earth’s Annual Global Mean Energy Budget, Bulletin of the American Meteorological Society Vol. 78, No. 2, February 1997 [Kiehl, 1997]

[ix] Heinz Hug, Der anthropogene Treibhauseffekt – eine spektroskopische Geringfügigkeit , Wiesbaden (August 2012) https://www.eike-klima-energie.eu/wp-content/uploads/2016/12/Hug-pdf-12-Sept-2012.pdf

#77As the post is linked to on facebook, discussion happen out there. I’ll post some revelant remarks: 1 Also collisions between molecules here are fast enough to nullify additional spontaneous emissions ” Interesting – do you have values for collision intervals and half-lives of CO2 excited states in the Infra-red in the lower Troposphere 2 the official ” theory is that the upper atmosphere is not co2 saturated so any increase there will additionally slow the escape if IR . it is also colder there. not saying i agree with this ,,,https://www.skepticalscience.com/saturated-co2-effect.htm ? 3 Actually water vapor does not absorb… Read more »

#78Reply van Frans van den Beemt aan vragenstellers (27-01-2019) 1)Collisions intervals are around 10^-8 s and CO2 15µm V2 vibration level a spontaneous emission relaxation time of around 0,74s. 2) CO2 15µm V2 vibration level starts to emit freely to space from around 76km-80km in the thermosphere at emission temperatures between 210K and 220K for the center lines. But the wings emit from the troposphere at much higher temperatures that vary with CO2 wavelength so a line by line calculation is necessary. Increase of CO2 concentration increases the emission height proportional with pressure and emission temperatures also differ. But around… Read more »

#79Frans can you explain where your calculations differ from Myhre et al and why tour approach is better?

#82Hans,

I assume that you refer to Myhre et al 1998 ( https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/98GL01908 ).

I’m afraid that their detailed calculations are not readily available and I doubt if we can get that comparising going. However, the message between the lines is clear. The calculations of Frans do invite independent robust duplication attempts. All details are available. If Frans is wrong, then he is wrong. Just anybody proof it.

#86Dear Hans Erren, I know the difference with IPCC in general and klimate models that make use of radiation transport equations (RTE). Most assume Local Thermodynamic Equilibrium (LTE). RTE under LTE lead in itself to 36K km-1 T laps-rate close to the surface. Convection processes are taken into account to correct for these results and the combination of RTE (LTE) and convection makes the results more close to what we measure. My approach differ (not better) in order to cope with complexity and to understand the role of CO2 in our atmosphere. The side wings of CO2 15micronmeter band are… Read more »

#80André, The formula for temperature in point 4 is just rewriting the definition for scale height (H). The ratio P/rho is equal to H * g. Inserting this expression in the temperature formula gives the definition of H= T * R/(g * n). The formula you mentioned does not ‘predict’ anything, it just expresses the gaslaw. André and Frans, When I examine several spectra in MODTRAN I deduce that the saturated P and R wings emit at ~20km (220K), just above the tropopause, the spike of the Q branch emits somewhat higher in the stratosphere, at ~35km (240K). The non-saturated… Read more »

#81Thanks, Dirk interesting.

I think that your first statement (“The ratio P/rho is equal to H * g.”) is identical to the computation of the dry adiabatic lapse rate (https://en.wikipedia.org/wiki/Lapse_rate#Dry_adiabatic_lapse_rate): dP=-ρgdZ

However I am not sure if this is related to Frans equation (4) about the pressure broadening normalized line shape function: (4) g(ϑ) = ½*π* abs{Δϑ}/{ (ϑ – ϑ0)^2 + ( Δϑ/2)^2 }

I agree that the thermosphere would not play a significant role in the energy balance of the atmosphere. It appears to be irrelevant.

#83André,

I referred to the formula of Frolly about calculating planetary surface temperatures… The temperature determines the P/rho ratio. The scale height in the atmosphere is the altitude for which the pressure decreases a factor e.

#85Thanks, I guess that would be 1000frolly. https://www.youtube.com/watch?v=V0jdPQ9aGbY

I intend to post on that later this year.

#87Dear Dirk, I agree the lower stratosphere contributes the most to the central CO2 emissions, already from a 40 km height looking down it seems that all emissions are gathered. In theory also the mesosphere contribute. So you are right. The temperature inversion in the lower stratosphere makes a higher CO2 concentration emits some more from the central CO2 lines or more cooling of the Earth system. The opposite is true for the far side wings especially the R branch, these two mechanism regulate the net cooling or warming, but because of convection processes and clouds the net outcome is… Read more »

#84Frans if you are using a 1 atmosphere layer with ambient CO2 concentrations, then to get to the total absorption path that exists in the earth’s atmosphere you must use a scale height of 8043 m.

I don’t see a scale height in your calculations.

#88Dear Hans Erren, I see no need because already in the first few meters CO2 absorbs the largest part, only the far side wings are not saturated and are absorbing in the whole troposphere.

#91But Frans it is the total absorption integral over the partially saturated wings that determines the logarithmic sensitivity.

#94Dear Hans Erren, that is right. The contribution of absorption for a certain path lenght is estimated.

#89I have a suggestion.I know it is a huge project that takes political courage and millions of dollars but we have invested to go to the moon why not invest to

Reinplant he Sahara dessert using only plants that produce more O2 than CO2 that will take CO2 from the air and increase even the ozon-layer

#90Dear Andre Nahr, it is not necessary to remove CO2 until we reach 1200 ppm, which is an indoor norm for buildings where people work and live. Best regards, Frans van den Beemt

#107De dynamische balans als uitgangspunt om onze impact op het klimaat te bekijken. Als er een dynamische balans is dan zijn het altijd dynamische structuren die deze balans beïnvloeden. Dat is een fysisch proces en als zodanig te herleiden. Hoe zit de dynamiek in elkaar, wat is wel dynamisch en wat is er niet dynamisch in dit proces, daar moeten we ons op focussen. Het klimaat is bij uitstek een dynamisch proces, je ziet dat deze dynamische balans door menselijke invloeden veranderd, maar ook door natuurlijke processen, dat onderscheidt kan wetenschappelijk worden bepaald. We zouden deze veranderingen in de dynamische… Read more »

#108Beste Gerrit Vermeer, Ik zal hier wat langer over na moeten denken, geef mij een week of zo. I have to think about this comment, it will. take me a week ar so to provide a reply.