WE MUST RENAME “SOCIAL DISTANCING”

March 30, 2020 § Leave a comment

Social distancing is a catchy phrase.  The distancing part is easily understood.  However, the implication is that all communication requiring bodily closeness is driven by social triggers.  This is not necessarily the case.  Business transactions entail close contact, especially in the west.  The shaking of hands, the exchanging of pleasantries and the ice breaker along the lines of “so, how ‘bout them Sox” (that particular line will be shelved for 2020, it seems, which is likely all to the good for the red variety of Sox, what with overpaying for injured stars and all), all require close bodily distance, the most egregious, under the circumstances, being the hand shake.

Today, in most places in the world, “shelter at home” orders discourage interaction based primarily on social objectives.  Sanctioned are trips, albeit careful ones, to the grocery stores, gas stations, hardware stores, pharmacies and curbside pickup of food at restaurants.  All these demand a measure of bodily proximity, which can easily be managed to minimize distance between individuals.  Shown below is an image from India, where the shopkeeper is taking steps.  Note the appropriation of a portion of the road!

Source: bangka.tribunnews.com retrieved March 30, 2020

Our farmers market in Carrboro, NC, did not go to these lengths.  But they separated the individual farmers by about three times the usual separation, instituted one-way pedestrian traffic (super decision whose value is immediately obvious: distancing is harder in cross flow), instructed all farmers on protection measures including produce handled only by glove equipped farmers* and dictated inter-customer distance, with roving enforcers.  Note, however, this was business distancing, not social, in the main.  The non-buying, chatting customer holding up the line last Saturday, comes to mind.  But, all good, nobody had anywhere to go anyway.

Social interaction, on the other hand, being expressly forbidden in person, has found avenues, new to some.  This is important.  Social connectivity may be more critical than ever.  Uncertainty is rife due to lack of information, poor information and information with agendas.  Just discussing with someone helps, especially if one lives alone.  All of us ought to be resolved to connect with someone each day.  Technology helps, but simple phone calls may work better for some.  Zoom parties are fully in play, as are virtual baby showers, birthdays and all manner of celebrations.  They may never replace the real deals, but then again, there is that chance.  Nothing substitutes for the warmth of direct personal contact (when permitted).  Hopefully, virtual social contact will be the exception in normal times.

Certainly, if Zoom (used generically here, take your pick on Skype, BlueJeans or any other) meetings prove effective even in business settings, two outcomes may outlive the emergency.  One is the increased appetite for remote workplaces.  This is already a trend, but the effectiveness could expand this, especially to businesses that did not already use the option.

The other is a decreased need to travel for meetings.  This last has always been on the cards with the ever-increasing sophistication in information technology.  But there is nothing quite like an extended “pilot test” to drive home the value.  Airlines and hotels will be the losers if this sticks.  Global warming could be a winner here, but only if the shift is large scale (aircraft have fewer options on fuel substitution than do automobiles). On the home front, the forced pilot test could make some couples realize that they were not as compatible as they believed.  Pervasive uncertainty and the need to make coordinated decisions will not help with frayed tempers.  Wiser counsel, or just another ear, would help.  This returns us to the need for social network access.  The opposite of social distancing, but without physical proximity.

India Prime Minister Modi recently made note of the distinction in his radio program Mann ki Baat, which loosely translates from the Hindi into “Something to think about”.  He referred to “increasing social distancing but reducing emotional distancing.”  Take your pick on alternatives to “social distancing”.  My Aussie nephew’s suggestion is “physical distancing”.

Vikram Rao

*You can’t touch this from “U can’t touch this” performed by MC Hammer 1990, written by MC Hammer (Stanley Burrell), Rick James and Alonzo Miller

SHEDDING LIGHT ON THE COVID-19 VIRUS

March 19, 2020 § 2 Comments

If enough of the light was at ultraviolet wavelengths, the virus would die.  This light, however, is an attempt to explain some of the science behind the virus and its effects.  I fully expect you folks to obtain fact or inference checks from physician scientists and am prepared for the comment onslaught.

A general caution is that very few sites, including this one, ought to be relied upon without verification.  The reputable sites include the National Institutes of Health (NIH) and in particular the National Institute of Allergy and Infectious Diseases (NIAID), the Center for Disease Control (CDC), and the World Health Organization (WHO).  Other sources are sites at top medical schools such as at Johns Hopkins, Stanford and Harvard. 

First the nomenclature.  COVID-19 is the disease resulting from the virus.  The virus is from the general family of coronaviruses, with this variant being named SARS-CoV-2.  SARS stands for Severe Acute Respiratory Syndrome.  The name being a bit of a mouthful, the WHO often refers to it as the “COVID-19 virus”.  The virus is related to those responsible for the recent outbreaks of SARS in 2002-2004 and Middle East Respiratory Syndrome (MERS) in 2012.

Structure and function

In common with other coronaviruses, they are spherical, with protein spikes sticking out about 12 nanometers (nm).  Resemblance to a crown informs the corona name.  They also have a striking resemblance to the fearsome medieval weapon, the mace.  In size they are reported to be in the range 50-150 nm, which places them roughly in the ultrafine classification of airborne aerosols.  However, deposition fractions in various parts of the respiratory tract cannot be presumed to be similar to those of particulate matter, even those coated with organic molecules.

A picture containing indoor, sitting, star, old

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SARS-CoV-2 transmission electron microscopy image, courtesy NIAID-RML

The image is of a virus isolated from a US patient.  The spiky proteins attach to receptors in human cells.  The mechanism is not unlike a lock and key.  The key of the virus protein needs a receptor lock to attach in order to then enter the cell.  Another analogy is docking of a spaceship to a space station.  Once this docking happens, the virus can enter the human cell.  Then it can replicate in the human cells and the disease is well on its way.  Recent research has shown that the receptor for SARS-CoV-2 is the same as that for the SARS virus.  That is the good news, because we know a lot about the original SARS.  The not so good news is that the binding affinity for this virus is ten to twenty times greater than for the original SARS (Wrapp et al. 2020).  This could explain why the human to human spread appears to be greater than was noted in the SARS outbreak.  Furthermore, despite the similarities in the structure and sequence of the protein spikes of the two viruses, three antibodies developed for SARS were not effective in binding to the SARS-CoV-2 protein spike.

A feature of the SARS-CoV-2 virus is that it is enveloped by a lipid (fat) layer (the “crown” protein extends beyond the lipid layer).  In this aspect the structure is like that of influenza viruses and the other coronaviruses (and unlike the diarrhea inducing rotavirus).  This is fortunate because soap and water will kill it.  Soap has a hydrophilic head and a lipophilic tail.  The tail penetrates the lipid layer and pries it apart, thus leading to the destruction of the viral genes, with all the fragments being washed away by the water.  This mechanism of action underlies the most important public health guideline for minimizing spread, washing of hands in soap and water for at least 20 seconds, taking care to wash between the fingers.  Hand sanitizers are believed effective if they contain at least 60% alcohol.  They too remove the lipid layer and cause the disintegration of the virus.

Except for the hand cleaning discussion, I did not get into disease avoidance.  For the rest you need to go to one of the reputable sites.  But I will note that my limited examination of the literature shows a flurry of scientific activity on several fronts.  These include studies of the immune response, development of a test to verify the presence of antibodies (UK), testing of intensity reduction drugs (example Tamiflu for influenza), and research on the ultimate prize: vaccines.  Keep in mind that folks are rushing to publish, in order to get the information for others to use, and so findings may be subject to revision.  The study linked above is based on a single patient, but still instructive. With all the stuff out there, caveat emptor!

Reference: Wrapp et al., (2020) Science 367, 1260–1263

Vikram Rao, March 19, 2020

ENERGY IN THE PRESIDENTIAL ELECTION

March 17, 2020 § 2 Comments

Energy showed up in the Democratic Presidential Debate, albeit not as a central issue; COVID-19 took care of that, closely followed by the ghosts of past senate votes.  Sanders wanted elimination of fossil fuels; I was not clear whether this referred only to domestic production or also domestic use.  For purposes of argument I will assume both.  There was little doubt that production was a target, because he called for an end to frac’ing, which is the primary means for domestic oil production.  But he also mentioned electric vehicles, giving weight to the second category.

When challenged by Sanders on the frac’ing issue, Biden used the time-honored debating technique of answering the question he wanted to hear.  Incidentally, this direct questioning of each other was tolerated and added spice.  Biden’s response was along the lines of Obama era policies: no drilling on federal lands and similar prohibitions.  Sanders too used the same technique during the climate change portion.  When asked by the moderator how he squared his banning frac’ing with the evidence that frac’ing was responsible for carbon reduction, through displacement of coal-based electricity, he simply ignored the question and gave some response that I forget.  He missed a bet by not proffering a “yes, but” response getting into the risks to human health, largely unrealized, but good debating material.  The pluses and minuses are in my 2016 book Shale Oil and Gas, the Promise and the Peril.  RTI Press will send you a free soft copy if you let me know.

How relevant was all this to the primary process?  Probably not much.  A quick search of opinions on the debate shows almost no mention of the points raised above.  I suspect Sanders raised the issues largely because they resonated well with his constituency.  Banning frac’ing is a classic progressive rallying cry.  Or used to be. Virtually zero mention in the talking head analyses indicates something.

But, will energy be a significant issue in the title bout?  Depends on who has the Democratic nomination.  Sanders would certainly make climate change an issue; Biden may as well, but likely not as stridently.  Sanders will use it to attack fossil fuels and frac’ing.  Trump’s support of the oil industry is solid, including permitting drilling on federal lands.  Nevertheless, he did, inexplicably, applaud the recent plummet in the price of oil, because it enabled cheaper gasoline. 

Biden, on the other hand, will likely evade oil and gas altogether.  If this issue comes up it will be because the Trump camp raises it. The only real policy differences with Trump appear to be on drilling (and likely, frac’ing) on federal lands and the Arctic (which will not involve frac’ing).  As to the latter, the likelihood of any oil company action in the Arctic at even USD 70 oil is minimal.  The reason is that developments in the Arctic, even the slightly more benign versions in the Alaska National Wildlife Refuge (ANWR), are expensive.  They would require stable high prices.  The recent near halving due to COVID-19 combined with the Russia/Saudi spat will provide scant comfort.  Used to be that wars were the primary reasons for volatility.  Now we have added a pandemic.

One final word on the issue of oil, gas and sustainable alternatives.  I have opined in these pages that oil must be displaced with dispatch in the transportation sector, and certainly the electricity sector.  If you are experiencing a doubletake on the second point, note that the Saudis currently use nearly a million barrels per day to produce electricity.  Diesel generators are the backups to power interruptions in innumerable locations.  In transportation, electric vehicles are the future.  But hurdles remain to speed the transition.  A complete transformation is at least 15 years away, 10 if we do most things right.  In the interim, continued domestic oil production is a national security issue. 

Natural gas is a different story.  Cheap natural gas from shale was arguably one of the most significant reasons for recovery from the recession of 2008.  The chemical industry relying on natural gas as a raw material, returned to our shores in droves, bringing jobs and prosperity.  Cheap natural gas rapidly displaced coal and dramatically reduced US carbon emissions.  The US stopped importing LNG, and this effectively dropped gas prices worldwide. Russian ability to use gas as a weapon of political will in Europe was severely curtailed.

These are facts and inferences that politicians of all stripes must internalize.  Also, that no form of energy comes without baggage.  Finally, affordable energy raises all boats of economic prosperity.

Vikram Rao, March 17, 2020

You may be right, and you may be wrong” from You May Be Right, 1980, performed and written by Billy Joel

OIL SINKS, GAS LIFTS

March 11, 2020 § 3 Comments

Saudi Arabia and Russia are playing a game of chicken with the price of oil.  After collaborating for a while in the cartel that came to be known as OPEC Plus, Russia did not agree to production curbs, even with the Saudis carrying most of the water.  The Saudis dropped their price to gain market share.  Today (March 11, 2020), the US benchmark West Texas Intermediate plummeted to USD 32 from about USD 60 at the start of the year.  This is a light oil.  Heavy crude, as from Canada, carries a discount in the vicinity of 25%.  Many operations, especially those heavily leveraged with debt, will be unsustainable.

Two factors are in play here.  The COVID-19 inspired reduction in industrial output and dampener on travel already put downward pressure on oil.  The Russia-Saudi spat merely poured fuel on the fire.  Russian breakeven price is USD 40, and the Saudi one is USD 80 (due to social costs; the production cost is in low single digits).  So, logic dictates this situation to not be long lived. Even if one of them blinks, the other factor will still depress oil usage. 

The associated recession is different from that in 2008.  Low demand was the big issue then.  This time the demand, spurred by low unemployment, is present and the supply is the issue, driven in large measure by China producing less goods during the COVID-19 crisis.

An interesting aspect of the situation is that one could expect natural gas prices to rise.  They have been depressed due to oversupply.  Excessive natural gas production has been an unintended consequence of shale oil production.  This oil, being very light (mixture of relatively small molecules) has a proportion of even smaller molecules associated with it.  These molecules are methane, ethane, propane and butane, in the main.  Collectively, these are known as wet natural gas.  The hot (perhaps not for long) Permian basin produces 2.2 billion cubic feet per day (bcfd) of this stuff with each 1.0 million barrels per day (bpd) of oil.  Until recently, the US was adding 1 million bpd of oil annually.  That additional “associated” gas was softening the gas market.  Expectation of continued shale oil increase heralded continued softness.  All that may change now. 

The print edition of the New York Times (March 10, 2020, B1) has a story on the oil standoff and the impact on US shale oil.  Curiously, an associated image is that of Shell’s partially constructed ethane cracker in Beaver County, PA (the product will be ethylene and associated plastics).  By implication (there is no explanation in the text) this will be compromised.  On the contrary, it is likely to command more guaranteed feedstock.  Ethane is a biproduct of “wet” shale gas, which is plentiful in that portion of western PA.  Shale gas development will likely get a lift from the firming of prices, and wet gas is more profitable.  That means more ethane supply for the cracker.  And possibly at lower prices; natural gas liquids prices are usually pegged to oil price.

In an odd twist, the Saudis announced a major entrée into shale gas production.  With 200 trillion cubic feet in reserves, they plan to produce 2.2 bcfd of shale gas by 2036.  This appears to be very wet, with 10 gallons NGL per mcf gas, which places it on the higher end of the richness scale of US deposits.  The liquids will be used to make chemicals, while the dry gas is destined to be burned for power.  That is the principal driver: to replace about 800,000 bpd of oil currently used to generate electricity.  That oil will now be available for export, adding to the glut (when it happens).  Shale oil has been a thorn in the side of the Saudi led OPEC.  Now, the Saudis plan to use the underlying technology to make more of their oil available for export.  US service companies will be doing the work. Ironies abound.

Vikram Rao

March 11, 2020

PS  The blog is back!!

THE KING IS DEAD, LONG LIVE THE KING

January 2, 2019 § 1 Comment

A recent story notes that natural gas drilling in 2018 has dropped by 87.7 %, from a peak in 2008.  Over the same period, natural gas production has increased by 58%.  Natural gas drilling is down to a whimper, but natural gas production continues to grow, year on year.  Had the gas production been from conventional offshore reservoirs, one could have hypothesized that a few large gas fields dominated production, despite fewer wells being drilled.  But most of the drilling for natural gas in this decadal period has been in shale, which does not produce high volumes, but each well is relatively inexpensive.  Before we launch into the explanation of the seeming anomaly, consider the impact of the result.

Natural gas production, largely from shale, was arguably the single biggest reason for lifting the US out of the last recession.  In the decade prior to the recession, US gas prices had fluctuated wildly from USD 2 per million BTU (MM BTU) to as much as USD 15 per MM BTU.  Nothing dampens the spirit of investors in capital driven industries more than unpredictability in the price of the key raw material.  Consequently, major industries, methanol producers for one, fled to countries with sustained low gas prices, such as Trinidad.  When shale gas went on the market in high volume, prices dropped, and stayed low, in the vicinity of USD 3 per MM BTU.  With predictions of sustained low prices, predictions which have held up now eight years later, industry returned to the US.  Liquified natural gas (LNG) imports were no longer necessary, and shortly thereafter, the US became an exporter of LNG.  For every citizen in the US, a lower fraction (sizable for many) of take-home pay went towards transportation and home heating and cooling.  The savings were spent on goods and services.  The recession was in retreat.

Shale oil picked up and became a major force by about 2013.  In 2015, the high production halved the world oil price and OPEC was marginalized.  The low oil price, together with the low natural gas price, contributed to the economic gains and a record stock market.  But gas prices stayed low despite steep reduction in gas exploitation, because gas supply continued to be high.  Curiously, and seemingly paradoxically, the reason is the steeply increasing oil production over the decade.  Over roughly the same period as the decline in gas drilling, oil production has increased from 5.0 MM bpd in 2008 to 11.6 MM bpd in 2018.  Now for the explanation as to why that caused gas production to rise.

Crude oil comprises of a mixture of molecules, with the bulk of them conforming to the formula CnH2n+2, where n is an integer.  Oil molecules break down over time in the host environment of high pressure and temperature.  The most thermally mature state is methane, with n=1.  Ethane, propane and butane, with n=2,3 and 4, respectively are the next more immature.  Shale oil is very light, as defined by API gravity.  Accordingly, the n’s are low numbers relative to heavier oils.  One could reasonably expect shale oil to be associated with some molecules at higher thermal maturities.  This is known as associated gas, and usually comprises methane in the main, together with the somewhat larger molecules with n=2-4 and more. Canadian heavy oil, on the other hand, could be expected to have little or no associated gas.  More shale oil production automatically means more shale gas production.

Recent data from the Permian, the hottest oil play in the US today, indicates that every MM Bpd of oil would have associated with it 2.2 billion cubic feet per day (bcfd) of gas.  If this statistic is taken to apply to all shale oil, as a first approximation, on would expect gas production to be 14.5 bcfd greater in 2018 than in 2008, from this source alone.  That translates into 5.3 tcf per year.  With no let up in shale oil production in sight, natural gas will continue to be produced.  Expect, therefore, for natural gas prices to remain at low to moderate levels, and a boon to the economy.  Shale gas drilling is, metaphorically speaking, dead, or at least a shadow of its formal self.  But natural gas remains the reigning monarch in assuring a healthy economy.

Vikram Rao

IS CARBON MITIGATION UNDER ATTACK?

August 21, 2018 § Leave a comment

The US administration appears to have fired a salvo against carbon mitigation.  We will examine the facts and muse on the likely true impact of the government action.  A recent story  discusses the implications of a directive seemingly buried in a memorandum on fuel economy standards from a month ago.  I am unable to find the one memorandum, but earlier documents for public comment are clear on a couple of measures, which are quoted in the linked story.  These include, freezing fuel economy standards to 2020 planned levels.

Ironically, this comes at a time when completely unprecedented forest fires rage worldwide.  Since this was more or less predicted by earlier temperature rise models, the increased frequency of fires is believed to have anthropogenic origins, as noted in a recent PNAS paper.  The impact of forest fires is profound.  The economic privation is high as is the long term impact on health.

 

Health impact of emissions from combustion

Even climate change deniers must accept the epidemiologically supported finding that airborne particulate matter (PM) is responsible for 6.5 million premature deaths, annually, worldwide.  Nearly two thirds of the mortality figure is attributed to wood burning for cooking and heating.  Forest fires are country cousins, in terms of type of particles emitted. They are spectacular and frightening, but in the overall scheme, currently account for minor contributions to airborne particulates.  But, to the extent they are driven by temperature rise, this contribution can only increase, even as other anthropogenic PM diminishes due to interventions.

 

Over 80% of airborne particulates are sourced from either the creation or use of energy.  On the consumption side, the biggest contributor in the US and Europe urban communities is automotive exhaust.  While diesel gets all the press, gasoline also is a contributor, particularly of ultrafine particles, which are especially toxic.  Both also produce NOx and organics, which are responsible for atmospheric reactions with the particles, often involving ozone and mediated by photochemical action, rendering them more toxic.  There ought to be little dispute that reducing these emissions ought to be a federal objective.  Two measures can accomplish that: engineered mitigation of emissions, such as better diesel particulate filters, or decreased use of fuel.  The objective of using less fuel, while obtaining the same utility, can only be attained with better engine efficiency.

Implications of the new guidelines

One of the directives is the relaxing of fuel economy standards, by holding them constant at 2020 levels.  This runs counter to the point made above, regarding means to reduce the impact of airborne particulate matter.  Since no companion guidelines are provided regarding PM capture, on these grounds alone, the new guidelines are unfriendly to the goal of reduced particulate emissions.  Admittedly, mortality figures associated with PM in the US are small compared to the world figure noted above.  A recent paper estimates it to be 138,000 annually in the early 21st century, about 5.1% of total deaths.  That is more than double those attributed to influenza and pneumonia, for which serious intervention measures exist.

In the linked story, the memorandum is quoted as stating that growth of natural gas and other alternatives to petroleum have reduced the need for imported oil, which “in turn affects the need of the nation to conserve energy.”  The gist of the story is that the administration believes that conserving oil is no longer in the national interest.  Without doubt the proliferation of cheap shale gas has allowed many commodities to be made profitably from natural gas, instead of from oil.  Since the US is a net importer of oil, such use of gas does reduce oil import.

However, due to shale production the US is already the leading producer of oil and gas.  Nevertheless, it still imports oil, while also exporting both fluids.  A lot of this trade is with Canada and Mexico.  I predict that within five years North America will be self-sufficient in oil and gas.  Accordingly, from the standpoint of national energy security, conservation is not needed (provided we don’t emasculate NAFTA in the energy sector).  But the plea in this blog is that it is needed to preserve the health of the citizenry.  And it is not conservation, per se, that we seek.  Simply, the more prudent use of energy for no less gratification.  Drive the same miles, stay just as warm (or cool), but do it more efficiently.

Vikram Rao

 

 

THE IMPORTANCE OF BEING SMALL*

August 3, 2018 § Leave a comment

In matters concerning airborne particulates, size certainly matters.  But in this realm smaller is more powerful, not necessarily in a good way.  In fact, decidedly not in a good way when it comes to toxicity.  In every step along the way from inception of the particle nucleus in the combustion process, to growth and transport, and finally to action on human organs, size plays a critical part.  And the smallest particles, less than 0.1 µm in size, are the most effective in each of those reactions.  The somewhat larger particles, up to an order of magnitude larger, are no slouches either, when it comes to toxicity to humans.  But the nanoparticles are the star act in a dark play.

Over 80% of anthropogenic airborne particulate matter (PM) results from either the production or use of energy.  The three principal players are coal combustion, automobiles and wood burning for cooking and heat.  The mechanism of PM production is common to all three.  It begins with the formation of a nucleus, followed by growth and completed by reactions with atmospheric constituents such as ozone, and mediated by photochemical action.

Particulate matter can range in size from a few nanometers to a hundred micrometers.  That covers four orders of magnitude.  The range is another few orders of magnitude greater when one considers surface area of the particles, instead of diameter.  Surface area is the key parameter in the chemical reactions affecting particles.  In chemical processes, for example, the best catalysts have high surface area to volume ratios.  Not surprisingly, size does matter in the impact on human endeavor.  Except, in the PM world, the littlest guys kick serious sand into the eyes of the large ones.

Diesel exhaust particles and mass distribution

Source: https://www.dieselnet.com/tech/dpm_size.php retrieved July 31, 2018

In considering the impact of ultrafine particles, one first needs to examine their prevalence.  The figure shows a typical distribution of particles in diesel exhaust.  On a mass basis, the majority are in the fine range (0.1 < x < 2.5 µm).  But, on a particle count basis, the majority are in the ultrafine range (x < 0.1 µm).  The mass associated with the bulk of the particles is a small fraction of the total mass emitted.  This is understandable, because it takes thousands of ultrafine particles to equal the mass of a single fine particle.  But, it calls into question regulations using mass as the variable.

This might appear to be splitting the proverbial hair.  But recognize that amelioration schemes rely on the regulatory variable.  With mass as the yardstick, a low mass count could simply be the result of removal of the coarse and fine particles.  This would leave the bulk of the particle count still in the medium, and if they are in fact the true bad actors, not much will have been achieved with the filtering.  All the foregoing argument applies only to health effects.  Visibility and climate change related parameters, such as radiative forcing, may be affected by the larger size PM.  Certainly, the recently reported reduction in solar panel efficiency by PM, will be more impacted by the larger particles, because the ultrafine PM is less likely to settle on to the panels.

Since the mass related regulation may continue to have utility, an additional parameter may be prudent to consider.  Two candidates are surface area and particle count.  Surface area to volume ratio increases dramatically with reduced size.  In a sense, just particle count by size will do the job.  But, in health-related outcomes, both size and surface area are separately in play.  Size determines the degree to which the particles enter and impact various organ systems.  Surface area likely mostly impacts from the standpoint that high surface area particles are scavengers for toxic substances such as volatile organic chemicals.  They are also more likely to have highly toxic reactive oxygen species on their surface.  From a public understanding and acceptance standpoint, the particle count may be simpler to communicate.  Multiple measuring devices are currently available to perform the count.

In summary, ultrafine particles play exceptional roles in the health impact of particulate matter.  Regulatory focus ought to shift to address this fact, to better inform intervention schemes.

Vikram Rao

*with apologies to Oscar Wilde

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