Best And Worst Time Of Day For Air Pollution

[Priceless]

... snip ... That pollution tends to stay close to the ground, say within a few 1,000 feet, is probably more due to the law of gravity than to inversions. An inversion will exacerbate this effect though, as has been said happened in CM in 2007

Sawasdee Khrup Khun Priceless,

Would you say that a lack of wind is usually associated with an "inversion" ?

If we accept that pollution obeys the laws of gravity, then isn't a logical corollary the assumption that for pollution to move somewhere else from where it originates: it must be first lifted up through the application of some kinetic energy, and second moved laterally by some kinetic energy ?

Naturally, we can assume that the smoke and hot-air of fires rising lift up particulate matter, and once lifted up into the atmosphere, wind must, logically, be the only "extra" force of kinetic energy that can cause it to move some distance ?

If we were in the middle ages, we could discuss the possibility of miniature beings with wings being born in rice burn-off. and mountain-side fires. and flying, and the possibility of flagellation and extreme spiritual techniques being used to neutralize these hypothetical flying particulate-demons ? But alas, the Unicorns, and the Mom-Makara of yore, and Upagruta in his ruby palace at the bottom of the sea, are gone for most us.

We beg you to dip into your "well of scientific knowledge," and speak to us about : wind

best, ~o:37;

Yes, an inversion is usually associated with a lack of wind. To quote from Wikipedia: "The air becomes stiller, hence the air becomes murky because dust and pollutants are no longer lifted from the surface."

/ Priceless

[Priceless]

Okay great then we have a non 'inversion' situation of pollutants being trapped in a valley. Lack of air flow or gravity being the more likely cause with less likely or unknown periods of infrequent or rare thermal inversion. Doesn't particularly change the spirit of the observations about relative concentrations of pollutants being trapped in the valley. Thanks for the clarification on terminology.

I noticed you just glossed over my postulated theory of greater <2.5 pm matter in CM due to combustion of hydrocarbons. If two different locations had comparable PM 10 levels but one area had significantly more 2.5 pm as a percentage of PM 10 then wouldn't the area with more 2.5 represent a greater health risk?

It's my understanding that burning hydrocarbons under pressure for example in vehicles creates these smaller and more health risky particles. Further it's my assumption that dense CM with its traffic and restaurant concentrations would be producing a lot more 2.5 pm hydrocarbon emissions than a agricultural region.

On the one hand the smaller pm 2.5 particles lodge deeply into the lungs and seem to be associated with more rapid cardiovascular damage as well as the increased transportion of toxins to the blood stream.

On the other hand I have generally made the assumption that agricultural burning tends to release larger less harmful particles because they are burned under less combustion pressure. Of course there are other factors like pesticides and oil based fertilizers being burned in agriculture settings which might offset the benefit of less PM 2.5.

One question I would find interesting is whether its better to be proximal to sources of agriculture burning or vehicle emissions and their relative health effects.

Kind of getting back to the spirit of the thread about avoiding health risks associated with variable levels of air pollution.

Winnie. Orang, Priceless? it's interesting topic to me because I want to live a long time in good health.

An interesting set of questions. I'll try to answer some to the best of my (limited) knowledge.

A/ "If two different locations had comparable PM 10 levels but one area had significantly more 2.5 pm as a percentage of PM 10 then wouldn't the area with more 2.5 represent a greater health risk?" From what I've read, it seems that your assumption is correct. This is also confirmed by standards, whenever they exist, usually setting much lower limits for PM<2.5 than for PM<10. E.g. the USEPA standard for daily average PM<10 is 150 µg/m³ while for PM<2.5 it is 35 µg/m³!

B/ "It's my understanding that burning hydrocarbons under pressure for example in vehicles creates these smaller and more health risky particles. Further it's my assumption that dense CM with its traffic and restaurant concentrations would be producing a lot more 2.5 pm hydrocarbon emissions than a agricultural region." I am not competent to reply to this one. It does however sound plausible, and would explain why, according to the WHO, PM<2.5 constitutes a greater percentage of total PM<10 pollution in industrialized countries than in developing ones.

Now for some arithmetical exercise:

It is rather clear that the pollution problem in Chiang Mai is a seasonal one. It also appears clear that the increased pollution during the winter months, in particular during February and March does not come from vehicle emissions. It therefore seems reasonable to look at the "low pollution" months of May - October for an approximation of vehicle-produced PM<2.5 pollution. Looking at 2009, the average pollution during these months was 24 µg/m³. If we assume that 75% of that is PM<2.5, that would work out as 18 µg/m³. I cannot see much reason why this should increase significantly during the "hazy season", since there are not that many more vehicles etc. If, to be on the safe side, we assume that it increases by half again, that would give us 27 µg/m³. The average pollution level during January - April and November - December of 2009 was 60 µg/m³. This would give us that average PM<2.5 during the six "hazy" months is about 27/60 = 45% of total PM<10 pollution. In total this seems to fit in with what WHO states is normal for urban areas in developing countries, which is 50%.

Please, PLEASE note that the above is based on a number of assumptions. There is no way to know without having actual measurements of PM<2.5 made, preferably over several years.

Based on the above assumptions and arithmetic and the actual measurements of PM<10 in the five provinces Chiang Mai, Chiang Rai, Lampang, Lamphun and Mae Hong Son for 2009, it is possible to calculate a theoretical yearly average exposure to PM<2.5 in these provinces (in µg/m³):

Chiang Mai: 22.4

Chiang Rai: 25.7

Lampang: 30.7

Lamphun: 23.7

Mae Hong Son: 23.9

Thailand does not have a standard for PM<2.5, but the EU "Target" which will become a "Limit" from 1 January 2015 is 25 µg/m³.

/ Priceless

[CobraSnakeNecktie]

Interesting and I agree about requiring actual measurement. My concern would be during the dry months PM 2.5 would accumulate and stay airborne due to lighter mass and thus more bio available for inhalation longer as compared to heavier particles in the PM 10 spectrum whose mass would tend to cause settling and binding to surface elements.

Hopefully the Thai authorities will continue this trend of greater monitoring. They seem to be trying to improve.

[MESmith]

Congratulations to you people who had some rain today.  On the eastern side of the valley we didn't get any.  We did get our a$$hole neighbour doing his bit to improve the air for everyone....  

And he's not Thai

[cloudhopper]

This just in from the US consulate in CM:

WARDEN MESSAGE: Air Quality in Northern Thailand

This message alerts U.S. citizens traveling to or residing in Northern

Thailand to the possibility that air quality in Chiang Mai and other

areas of Northern Thailand might pose a health threat during the dry

season, from March until June, when these areas typically experience

periods of poor air quality. Smoke and particulate matter can irritate

eyes and respiratory systems and worsen heart and respiratory diseases.

People who have heart or respiratory disease, older adults, and children

are the most likely to experience health problems when air quality is

poor.

You should be aware of the local Air Quality Index (AQI) and take

appropriate measures to minimize the impact on your and your family's

health. The Thai government's Pollution Control Department calculates

the AQI daily and posts measurements at the following website:

http://www.pcd.go.th/AirQuality/Regional/Default.cfm

The U.S. Environmental Protection Agency explains the Air Quality Index

(AQI) at the following website:

http://airnow.gov/index.cfm?action=aqibasics.aqi.

The recommendations of U.S. Centers for Disease Control and Prevention

(CDC) for actions to take during periods of poor air quality are found

at: http://www.bt.cdc.gov/disasters/wildfires/facts.asp.

To obtain Centers for Disease Control and Prevention (CDC) travel

notices, you may dial the CDC at 1-800-CDC-INFO (1-800-232-4636) from

within the U.S., and at 1-404-639-3534 from overseas, or visit their

website at http://www.cdc.gov/travel.

Edited March 12, 2010 by cloudhopper