Date: Tue, 25 Mar 2008 10:39:42 -0600
From: Dan Long
Subject: Re: 2.5m obslog 20080324 (MJD 54550)
    Let me echo Steph's comments on pollen.  They become especially
important if it is decided not to recoat the primary this year.
    I'd also like to add that your decision to be cautious and close
when the combination of dust and humidity became elevated was a good
one.  When the humidity is above about 60% (or the temperature of the
mirror is within about 10 C of the dewpoint), we cannot CO2 clean the
mirror due to the risk of fogging the mirror.  If the air doesn't dry
significantly during the day, any dust that accumulates in humid
conditions will have to remain on the mirror longer, giving it more
of a chance to adhere to the coating, which is pretty much exactly
what you don't want.
				Cheers,
				  Dan
>As we move into Spring, please remember to be alert for pollen
>masquerading as dust. It is too early for pine pollen yet (I think),
>but it won't be too long before the pine trees release their pollen
>for a week or two. It is really bad stuff to get on mirror surfaces,
>because it is sticky. So, during the Springtime, if the dust counts
>go up, check car surfaces to see if any of the dust has a yellowish
>hue. If it does, don't use accumulated dust counts, but just close
>as soon as the dust levels get high. If a flashlight test confirms
>pollen sized particles in the air, close. If anyone has an allergy
>to pine pollen, pay attention to their sneezes :-)
>
>Steph
>On Mar 25, 2008, at 6:20 AM, Dan Oravetz wrote:
>
>>
>>Integrated dust count ~20,000 dust-hours with humidity between 40%
>>and 50% and
>>sometimes over 50%.  Please check the mirrors.
>>
>
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