Wednesday, May 30, 2012

Previous aerosol monitoring in the United States

Looking over a few aerosol papers now:

Here's a paper that measures the content of PM2.5 from JGR: Seasonal composition of remote and urban fine particulate matter in the United States

So what did they find? Well, for starters just about anything you can imagine is in a aerosol, including salts, various forms of carbon, heavy metal (i.e. this paper), and acids (SO2, NO2, HCl, etc). Here the authors narrowed their radar to "ammonium sulfate, ammonium nitrate, particulate organic matter, light-absorbing carbon, mineral soil, and sea salt".

A problem one is faced when sampling is "do I choose a weighted average based on population density or maintain a uniform geographic scattering?" The answer here would appear to be geared to the former; there was a roughly 50/50 split between urban and rural analysis (176 vs 168) since there is a even divide of urban and rural populations (but increasingly urban).

The first two aerosols listed ((NH4)2SO4 and (NH4NO3) are specific chemicals. The four thereafter (POM, LAC, MS, SS) are categories, not individual species. What is inside them (which are, in turn, inside aerosols)?

Sulfate and Nitrate Anions 

Determined "from ion chromatography using a nylon filter... preceded with a sodium carbonate coated denuder". The anions sulfate and nitrate are assumed to be neutralized by the ammonium cation (but not necessarily true: other cations could associate with these species eg Na or CaCO3). Relative to the total aerosol mass, sulfate accounted for 40%, up to 60%. Nitrates were smaller, at 10-20%.

Mineral Soil (MS)

For mineral soil we have as components Al2O3, SiO2, CaO, K2O, FeO, Fe2O3, and TiO2. These are found via X-ray fluorescence (XRF).

Light-absorbing carbon (LAC)

For LAC we have a combination of 'black' carbon (aka BC or 'soot') and 'brown' carbon.  Black carbon exists as an aggregate of 10-50 nm carbon particles. These structures are skeletally seen as elemental carbon, much of it graphite (plus other trappings found in the structure: aromatic hydrocarbons and some other aliphatics). Since carbon is the backbone of soot, elemental carbon (EC) is another means of defining these particles. This alternate classification is a functional one rather than chemical or physical. The paper states that "We use “LAC” instead of “EC” based on the recommendation of Bond and Bergstrom [2006] [proposing an absorption cross section of α(550 nm) = 7.5(1.2) m2 g−1] and to avoid possible improper classification". But 'improper' is subjective. From the 2006 paper by Andreae et al Black carbon or brown carbon? The nature of light-absorbing carbonaceous aerosols
Both “BC” and “EC” can only be regarded as “proxies” for the concentration of soot carbon, whose accuracies depend on the similarity between atmospheric soot and the species used for calibration. If atmospheric soot were pure graphite and all the methods were calibrated against graphite, “BC” and “EC” readings would give exactly the mass concentration of soot carbon as intended. Since, however, graphite is only a trace component of atmospheric soot, “BC” and “EC” measurements usually give different results, which have possibly little in common with the “true” mass concentrations of atmospheric soot par ticles. However, in the literature these discrepancies are usually disregarded and the terms “BC” and “EC” are used interchangeably as synonyms for soot carbon.
Not to go off-topic but some of the contention could stem from debates in application of BC/EC to climate change models. Climate change is something everyone wants to throw in their two cents, and debating exact light-scattering parameters lays open some targets. Ultimately the definition hovers close to the notion of that carbon which absorbs light.

Brown carbon absorbs shorter wavelengths than black carbon (less than 550 nm, into the UV spectrum), and appears brown in color. It is composed of "light-absorbing organic matter in atmospheric aerosols of various origins, e.g., soil humics, HULIS (humic-like substances), tarry materials from combustion, bioaerosols"

How is LAC measured? Thermo-analysis is one way, whereby the sample is progressively heated and all carbon is converted to CO2 and quantified. The original paper discussed here uses thermal desorption from quartz fibres. But since the point of defining LAC is to obtain the light-absorbing component, cross-sectional visible light absorption is an intuitive alternate method of measure. The problem is, however, that light absorption methods have higher measurement errors/lower detection limits. Andreae et al discuss this problem comparing various absorption instruments.

Relative mass to total PM2.5 weight is small, about 3-15% (errors are large due to the small amounts of LAC present in aerosols)

Particulate organic matter (POM):

Particulate organic matter was assumed to related to total molecular weight of 1.8 per unit mass total carbon (changed from 1.4 from an earlier publication). This value is empirical and can vary widely (e.g. 1.2 to 2.6). The 'additional' mass comes from O, N, and H and varies with aerosol age/location. Carbon in POM is assumed to be equivalent to organic carbon (OC) and is determined by thermal desorption techniques. In other words the difference between POM and LAC in this study is merely the temperature at which the carbon is oxidized to CO2; a threshold temperature must be established and therefore it is somewhat an arbitrary division (cutoff of about 650 Celsius).

POM constitutes a relatively large percentage of total PM2.5 mass (40-75%).

Sea Salt (SS)

Sea salt concentrations were determined by measuring chlorine ion concentrations and multiplying by the factor 1.8. Since only one ion represents the total salt ion concentration, there is a chance errors are present if chlorine escapes from reaction with gaseous nitric acid.

Sea salt constitutes a medium percentage of total PM2.5 mass: 10-20% in coastal and <5% in continental (land-locked areas).


At this stage I'm as interested in the results as the methods. Nevertheless the rural/urban divide piques my interest  as this is my project's direction, i.e. to compare and contrast 'clean' country air and 'dirty' city air. I use quotation marks because sometimes a city can be cleaner than the country, especially if near a farm, waste depot, factory, etc. And cities can be very clean if electrically-driven public transportation dominates (such as the solar-powered city Freiburg, Germany). Here are the comparisons

Ammonium sulfate: no strong difference in city/country divide, but east had much more sulfate than western US. Likely this is because of the higher coal power plant density on the eastern half.

Ammonium nitrate: Urban levels were much higher than rural (4-5 times) and increased in the mid-western US, reflecting significant fertilizer use. High urban levels are not easily explained. The paper says maybe it's due to elevation differences (between rural/urban measurement methods?)

POM: Very much higher in urban environments (2-5 times), likely due to fuel combustion and outdoor cooking (my guess since maxima is in summer).

LAC: Urban LAC was much higher that rural levels. LAC is a combustion product, hence emissions are concentrated with human population.

Soil: Higher levels in 'dustier' areas, i.e. varies on the region of US (i.e. Death Valley is high in aerosol soil content). No strong differences were seen in city vs. country, within a given landscape.

Sea salt: Tied to proximity with oceans, not cities

Aside: Another publication (this one by Vandereli Martins et al) shows what PM2.5 light absorption looks like (for 250 to 2500 nm light):

Monday, May 28, 2012

Enviroment Canada health monitoring

Next month I will begin a post doc at the university of Dalhousie, Halifax. I've been looking forward to starting a new project, so here we go.

Environment Canada is facing some serious cuts this year. It's no surprise that the government is tithing its departments equally after the budget was announced, yet some environmental studies have been in place for decades, such as the Experimental Lake Area (studies include the spread of mercury pollution in a marsh environment, METAALICUS).

The National Air Pollution Surveillance Program (NAPS) is a subsidiary of EC, though it looks like some projects are facing cuts. The team collectively monitors air quality in most provinces. This includes Alberta. It seems the federal government might not be all that curious how polluting the tar sands are. Hmmm... Fortunately there are many sub-programs withing the NAPS, some of which monitor general air quality in major cities, like what I'll be doing. The air quality health index (AQHI) checks on levels of O3, NO2, and (particulate matter) PM10 / PM2.5 within Canada and reported on a scale of 1-10. The last of these quantities, PM2.5, is my future specialty. I have to say browsing the EC website, it's not easy to find the precise formula they use. For instance in the FAQ section, the answer to "How is the AQHI calculated?" they reply
In the development of the Air Quality Health Index, a formula that combined these three pollutants were [sic] found to be the best indicator of the health risk of the combined impact of the mix of pollutants in the air.
But what's the formula? I found it in the publication titled A New Multipollutant, No-Threshold Air Quality Health Index Based on Short-Term Associations Observed in Daily Time-Series Analyses:

I can see why this information isn't listed prominently on EC's website, though the paper should have been linked via the FAQ. What this formula attempts is take an incredibly complex concept -surplus urban deaths from three major pollutant sources- and translate the information into a scale between 1 and 10(+). A huge task; naturally the devil is in the details. Herein we find the interesting and contentious data: they lie in the regression coefficients that link pollutants to mortality. You have to dig further to find what the excess mortality is for a given pollutant. The authors state
the percent increase in mortality associated with the mean concentration of each pollutant was: CO (1.8 ppm) = 0.83 +/- 0.45; NO2 (33.6 ppb) = 2.08 +/- 1.19; O3 (29.9 ppb) = 1.82 +/- 0.61; PM10 (25 ug/m3) = 2.20 +/- 1.10; PM2.5 (12.8 ug/m3) = 1.69 +/- 0.79 and SO2 (13.7 ppb) = 0.55 +/- 0.33
Hence for the given concentrations of pollutants listed above, that amount of additional pollution will cause such-and-such percent excess deaths. This is a complex idea that isn't discussed directly in the above-quoted paper, only reported (there would be no room to discuss them). Regardless, what the numbers mean to state is the relation between pollutant of concentration X and their associated danger. For low concentrations this is roughly linear: ebx-1 = bx for bx <<1. For a doubling of carbon monoxide in the air (say 1.8 ppm to 3.6 ppm) there is a doubling of danger of sudden (?) death from 0.83 % to 1.66% for the deaths already present in a city's population as a whole (defined as m in the paper). Likely cause of the 'excess' deaths? Cardiac arrest [NB: Continual breathing of CO above 1,000 ppm leads to death within hours; no more than 9 ppm should ever be breathed for any significant period of time].

These numbers are not without controversy. For starters we must accept there is even potentially a single attributable risk number for each separate pollutant, nearly as difficult as associating an IQ with someone's intelligence (but with more scientific grounding). Also there can be debate as to where (elevation, which cities) and when (time of day/year) the data is measured, and who exactly declares if such deaths occur (post-mortem by a team of doctors/other specialists?). These are all difficult topics to agree upon. Many co-factors must be eliminated (death from smoking, other diseases etc) and I see this reflected in the very broad 2-sigma (95%) confidence intervals; pollutants' pre-factors have a 30-60% uncertainty.

The rest of the formulaic conversion (from pollution levels to the AQHI) is accounting; these values are converted into percents while keeping the averages representative of large cities and establishing confidence limits, sensitivity tests, etc. Recall that CO and SO2 have not been included in the AQHI; this is because they were found too well correlated with the other pollutants (hence did not provide an independent measure). But all this detail is the least of the confusions for curious readers, as the EC FAQ informs us that every place region has a different formula to consider:
The American index is standards-based and emphasizes the impact of a single pollutant, much in the same way as provincial  air quality indices have done up until now, The different jurisdictions have different standards and in addition the US uses different scales and categories.
See for instance, the EPA's Air Quality System (AQS).

Things to ask kids

Hey kids, do you know science? Here's a question that's obvious enough, but you have to understand what colour really is. A good one for the classroom. So how come...

if you shine white light through a prism you get all the colors of the rainbow, but if you mix all your pain colors (of the rainbow) together you get black paint, not white?

Thursday, May 24, 2012

Canada in trouble

We used to get a kick out of crazy US politics, now they're watching us with the same kick. Well, most probably are not. Still, major American publications are noticing our activities, and they're not our proudest moments. These two are particularly notable.

First, Nature's mention of our government's closing of the Experimental Lakes Area (ELA):
The Canadian government has cancelled its funding for the ELA, a research site in northwestern Ontario that has led to the re-shaping of international policies. It is the latest target in a string of research programmes to have been scaled back, shut down or left in limbo in the wake of massive cuts to this year’s federal budget.
Secondly the New York Times printed an opinion piece (by UdM profs) of Quebec's quashing of student protests:
Americans should take note of what is happening across the quiet northern border. Canada used to seem a progressive and just neighbor, but the picture today looks less rosy. One of its provinces has gone rogue, trampling basic democratic rights in an effort to end student protests against the Quebec provincial government’s plan to raise tuition fees by 75 percent..
[Bill 78] will remain in force only until July 1, 2013. The short duration says it all.
Americans traveling to Quebec this summer should know they are entering a province that rides roughshod over its citizens’ fundamental freedoms.
Wish I could say these were isolated incidents but they're part of a growing trend. I'm glad Quebeckers are not taking this lying down; the provincial government should be reminded of its  decision daily, and painfully. I'm sad to see that Ottawan's has no similar protesting. The $10B overspending jet fighter fiasco alone should have been enough to cause a serious, and justified, riot.

So yes, Canada is a scary place right now. If this continues I'm thinking of leaving sometime in the future. I feel the present Canada would waste away any scientific breakthroughs anyway. If you're working as an intellectual you might see the country like a rat in a sinking ship. I've begun an interest in 1930s fascism for obvious reasons; I want to know what we're in for.

Monday, May 7, 2012

Big versus small science

I wrote a comment on this blog post regarding big versus small science. I'm re-posting my comment here. In summary, big science is not a trickle-down effect (for the benefit of small science). Rather, small science is a trickle up to supporting big-picture projects. (Would anyone fund a space mission unless they were not already > 99.9999...% certain of the basic principles involved?). Big science's job is to see how all the small parts fit together; there's always a surprise or two lurking about, not to mention the satisfaction of seeing the visible fruits of many labors. This is also why the moon mission ended so abruptly, as so little 'new' was discovered. Ironically that means it was a success. Here's my comments, as related to big-budget movies:
Absolutely agree there should be a mix of the big and small science projects. I like to use the Hollywood film industry as an example; they fund medium-to-big productions, which sometimes flop but overall make a profit. If art (movies in this case) can make money, we sure as heck should expect science to think along the same lines.

Small budget films get their funding from a multitude of sources, government grants, private donors, collected donations, personal cash etc. If a small-budget director shows promise, he/she is often given the chance to work with bigger projects (Peter Jackson), or at least more grants. Some prefer to stay small (Jim Jarmusch or Guy Maddin) and others actually do worse with more funding (think of David Lynch with his 'Dune'). It's a pyramid, but a stable one that satisfies a maximum of tastes and talents (big-budget films are necessarily fewer in number). And no matter how many small movies you fund (even 1000s of them), a production like "Avatar" or LOTR will never spontaneously appear from the mix; Bollywood for instance is scant on mass-appeal epics.

Small and big budget science will forever maintain certain distinctions. Funding both means we get the benefits from both. Big science takes fewer chances but the results are less contested (the Manhattan project, for one). How much does the world 'need' another moon mission or Avatar film? Maybe that's a philosophical question. I'm happy with some of each. 
Once the moon missions were over, there was so little 'new' discovered that it was clear the next big science project would have to look along very different lines. In a similar vein big-budget films do not signal the beginning but rather the end to a style/special effects era. Mars rovers are technically 'small' science, in that the only new, scientific portion came with the rover itself (and they had a comparatively small budget: $250 M). Before the space race was the invention of the A and H bombs; scientists were excited by these for 10 years (1939-1949). Afterward they moved on to the moon missions and rocket design (which were very challenging). After the mid 1970s when space became less interesting (and rockets were standardized) it was particle colliers that took over our big-science interest. Now we're at the tail end of this too. What could be our next big budget production? Likely space probes will grow in scale (MESSENGER, Cassini, Mars rovers, or the planet-finding Kepler), as they have all been very successful medium-budget ventures. But the question remains unanswered: how will we try attempt a big budget version of any one of these?

Despite the power of the LHC it is already falling off the logarithmic curve. No larger projects lurk on the horizon, which would take 20+ years to build anyway. We have reached the zenith of this technology.

Sunday, May 6, 2012

Tommy Douglas

I was browsing through some recent history and came across this little gem:
Surely the continued policy of allowing the subnormal family to bring in to the world large numbers of individuals to fill our jails and mental institutions and to live upon charity is one of consummate folly.
The idea behind the quote is that the mentally feeble reproduce more than the intelligent. The quote itself is from Tommy Douglas, the first leader of the NDP from his master's thesis The Problems of the Subnormal Family. It's outlined here in the National Post. Interesting, shocking material that's not often discussed. He did not try to implement these policies later in life, and when the thesis was published (1933) he was in his late 20s, old enough to have a balanced opinion.

Also in 1968 he described homosexuality as "a mental illness, it's a psychiatric condition, which ought to be treated sympathetically by psychiatrists and social workers".

Then again, he was advocating that gays not be thrown in prison (homosexuality was then implicitly a crime in Canada). Moral relativism it would appear. Strangely when I googled "Tommy Douglas homosexuality" I found a bunch of blog posts about these quotes but less-so by media outlets. Anyhow, this is a bit late to unearth something know for so long. Still, he's father of medicare but maybe not the greatest guy that ever lived.