[pam-users] Question about the PAM light source

[pam-users]

Hi Qi,

It is possible to achieve a photon flux of about 6e15 photons/cm2/s with all four lamps turned on at maximum intensity. For more details, see Section 2.2.1 and Fig. S4 of this paper:

Lambe, A. T., Krechmer, J. E., Peng, Z., Casar, J., Carrasquillo, A. J., Raff, J. D., Jimenez, J. L., and Worsnop, D. R.: HOx and NOx production in oxidation flow reactors via photolysis of isopropyl nitrite, isopropyl nitrite-d7, and 1,3-propyl dinitrite at λ = 254, 350, and 369 nm, Atmos. Meas. Tech., 12, 299-311, https://doi.org/10.5194/amt-12-299-2019, 2019. Abstract<https://www.atmos-meas-tech.net/12/299/2019/amt-12-299-2019.html>, PDF <https://www.atmos-meas-tech.net/12/299/2019/amt-12-299-2019.pdf> and Supplement<https://www.atmos-meas-tech.net/12/299/2019/amt-12-299-2019-supplement.pdf>.

I have heard of groups using flow rates as low as 2-3 L/min. It might be also possible to operate at lower rates, but I have not attempted this myself, and have not received feedback from others that might have tried it. If you like, you are welcome to email aerodyne-pam-users at lists.aerodyne.com<mailto:aerodyne-pam-users at lists.aerodyne.com> to poll other OFR users on their experience. Or if you prefer, I can ask the question myself on your behalf.

Andy



From: Qi Zhang <dkwzhang at ucdavis.edu>
Sent: Wednesday, May 5, 2021 4:48 PM
To: Andy Lambe <lambe at aerodyne.com>
Subject: RE: Question about the PAM light source

Hi Andy,

Thanks much for sharing the information.  I have been trying to get funds to purchase a PAM. One of the applications of PAM I am considering is to study phenol oxidation in aerosol water under simulated sunlight illumination. The idea is to extend the works my group has done on phenol reactions in diluted aqueous solution representative of fog/cloud waters. The photoreactor we use for aqueous reactions has a set of light tubes installed along the chamber wall to generate photons > 300 nm.  To mimic sunlight spectrum, we use a combination of lamps that emit lights in different wavelength range. We see fast aqueous oxidation of phenols and by changing solution concentration, we see evidence of changing reaction rates as well as product composition as a result of increase of solution concentration and the presence of salts. This suggests that aqueous reactions of phenols In cloud water are quite different than those in aerosol water.

Using our photoreactor approach, we cannot reach highly concentrated condition relevant to ambient aerosol water.  So I thought about using PAM to explore such reactions. I think by increasing humidity inside the chamber, we may be able to expose hydrated phenol-containing particles to lights inside PAM, thus are able to examine the decay of phenols and production of SOA under aerosol water conditions. This is the reason I am interested in having lamps that produce sunlight relevant lights. It is good to know there are indeed such lamps. Either of the three lamps you shared could work. We need to do so calculations to check is the light intensity is strong enough to allow for fast enough reaction. BTW, what’s the highest residence time workable for PAM? I know the chamber size is 13 L, so at AMS flow rate of 0.1 L/min, we can get to 130 min max. Of cause particle loss would be a concern, but we can try to correct for that.

I’d very much like to hear your thoughts on the plan mentioned above. Thanks!

Qi

From: Andy Lambe <lambe at aerodyne.com<mailto:lambe at aerodyne.com>>
Sent: Tuesday, May 4, 2021 8:57 PM
To: Qi Zhang <dkwzhang at ucdavis.edu<mailto:dkwzhang at ucdavis.edu>>
Subject: RE: Question about the PAM light source

Hi Qi,
We have lights emitting in the UVB or UVA – see attached.
Other wavelengths are available from the manufacturer, but the above are normally stocked at Aerodyne.
They won’t work as well for generating OH “the normal way” – mostly useful for photolysis of isopropyl nitrite (high-NOx OH source), or chlorine (Cl source), but maybe you are considering doing something else with them (?)
Let me know more details about what you’re interested in, and I’ll try to help.
Andy

From: Qi Zhang <dkwzhang at ucdavis.edu<mailto:dkwzhang at ucdavis.edu>>
Sent: Tuesday, May 4, 2021 11:48 PM
To: Andy Lambe <lambe at aerodyne.com<mailto:lambe at aerodyne.com>>
Subject: Question about the PAM light source

Hi Andy,

I have a quick question about the light source for PAM – are there lamps used in PAM that can generate lights mimicking solar spectrum or above 290 nm?  If not, are you aware of efforts to make that happen? Thanks!

Qi

Qi Zhang
===========================================
Professor
4251A Meyer Hall (Office), 4422 Meyer Hall (Lab)
Department of Environmental Toxicology
University of California, Davis, CA 95616
Email: dkwzhang at ucdavis.edu<mailto:dkwzhang at ucdavis.edu>
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