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Query on the unit conversion formula of the aerosol species output of WRF-Chem simulation

A

Ankan

Member
Dear everyone,
I have some doubts about the unit conversion of aerosol species. I ran WRF-Chem using the RADM2-MADE/SORGAM chemical mechanism. I viewed the output using the MATLAB command ncdisp. Some portions of the displayed lines are as follows:
eci
Size: 405x415x34x217
Dimensions: west_east,south_north,bottom_top,Time
Datatype: single
Attributes:
FieldType = 104
MemoryOrder = 'XYZ'
description = 'Elemental carbon Aitken mode'
units = 'ug/kg-dryair'
stagger = ''
coordinates = 'XLONG XLAT XTIME'
ecj
Size: 405x415x34x217
Dimensions: west_east,south_north,bottom_top,Time
Datatype: single
Attributes:
FieldType = 104
MemoryOrder = 'XYZ'
description = 'Elemental carbon Acc. mode'
units = 'ug/kg-dryair'
stagger = ''
coordinates = 'XLONG XLAT XTIME'
Here, you can see that the units are in 'ug/kg-dry air'. I guess that it should be a mixing ratio. However, I have gone through many research papers, and in most studies, aerosol species concentration in 'ug/m3' is used. I also didn't find any dataset that has units of 'ug/kg-dry air' that can be validated with the model output. Therefore, I would like to convert the unit of 'ug/kg-dry air' to 'ug/m3'. So, can anyone please tell me if there is any standard method to do this? Also, can anyone suggest to me any reanalysis or observational datasets of aerosol (e.g., BC) concentration that can be validated with the model results? That will be very helpful for me. I am really looking forward to hearing from you. Thank you for your time and consideration.
With regards,
Ankan
 
Ankan,

You need to multiple the mass mixing ration by air density (kg/m3), where rho = (1/287)*P/T.

Aerosol datasets will depend on the region of interest, e.g., the IMPROVE network over the US has BC.

Jordan
 
Dear @jordanschnell,
Thank you for providing the formula. My region of interest is Indian region. Do you know any observation or reanalysis dataset of BC concentration for this region?
With regards,
Ankan
 
Hi Ankan,

You could try India’s Central Pollution Control Board (CPCB), I don't remember if they have BC specifically. Otherwise you can search for field campaigns and modify your time period.

Jordan
 
jordanschnell said:
Ankan,

You need to multiple the mass mixing ration by air density (kg/m3), where rho = (1/287)*P/T.

Aerosol datasets will depend on the region of interest, e.g., the IMPROVE network over the US has BC.

Jordan
Click to expand...
@jordanschnell
Hi Jordan,

Would you please explain more about the variable in this equation? What are rho, P, and T, please?
You pointed to "multiply the mass mixing ratio by air density". So if I have NH4 concentration in ug/kg dry (say 1.4 ug/kg dry air) then the value of NH4 would multiply by 1.287 (1.4*1.287)?

Thank you in advance.
 
@jordanschnell
I have another question.
Air density is not a constant at different pressure levels. So I want to have concentration at different pressure levels what should be done, please?
 
Hi Seti,

The calculation of air density is the same for any given level, you just need to use the values at those levels. Density = (1/287) * pressure / temperature. These are fundamental quantities and calculations that I would recommend familiarizing yourself with.

Jordan
 
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