With drop in LA’s vehicular aerosol pollution, vegetation emerges as major source

[The ghost of Ronald Reagan makes an appearance~cr]

Plants that emit lots of isoprenes may be causing unhealthful aerosol levels during heat waves


Research News


California’s restrictions on vehicle emissions have been so effective that in at least one urban area, Los Angeles, the most concerning source of dangerous aerosol pollution may well be trees and other green plants, according to a new study by University of California, Berkeley, chemists.

Aerosols — particles of hydrocarbons referred to as PM2.5 because they are smaller than 2.5 microns in diameter and easily lodge in the lungs — are proven to cause cardiovascular and respiratory problems.

As a result of strict vehicle emissions laws, organic aerosol levels have been significantly reduced throughout the United States, but the drop has been particularly dramatic in Los Angeles, which started out at a higher level.

Based on pollution measurements over the past 20 years, the UC Berkeley scientists found that concentrations of PM2.5 in the Los Angeles basin in 2012 were half what they were in 1999. As a result, from 2016 to 2018, there were almost no PM2.5 violations in the area when temperatures were low, below 68 degrees Fahrenheit. But at warmer temperatures, aerosol concentrations rose — over the same time period, 70% to 80% of days over 100 F exceeded the National Ambient Air Quality Standard (NAAQS) threshold.

“The positive news is that, where we did understand the source and we took action, that action has been incredibly effective,” said Ronald Cohen, an atmospheric chemist and UC Berkeley professor of chemistry. “Twenty years ago, just about every day in LA was in violation of a health-based standard. And now it is only the hot days.”

As vehicle organic chemicals — compounds of carcinogens such as benzene and toluene –dropped, air quality experts focused on other potential sources of aerosols in those cities with unhealthful levels. Many researchers believe that personal care and household cleaning products — some seemingly as benign as the citrus scent limonene — may be the culprit. Given the temperature dependence of aerosol levels in Los Angeles, Cohen doubts that.

“There is a growing consensus that, as cars became unimportant, household chemicals are dominating the source of organics to the atmosphere and, therefore, dominating the source of aerosols,” he said. “I am saying that I don’t understand how aerosols from these chemicals could be temperature-dependent, and, therefore, I think it is likely something else. And trees are a good candidate.”

Plants are known to release more organic chemicals as the temperature rises and in many forested areas trees are the source of organic chemicals that combine with human-produced nitrogen oxides to form aerosol. President Ronald Reagan was partially correct when he infamously stated in 1981 that, “Trees cause more pollution than automobiles do.” At the time, scientists were learning about the role of forests surrounding Atlanta in causing that city’s air pollution.

Cohen and former Berkeley master’s degree student Clara Nussbaumer reviewed organic chemical emissions from various plants known to grow or be cultivated in the Los Angeles area and found that some, such as the city’s iconic Mexican fan palms, produce lots of volatile organic compounds. Oak trees are also high emitters of organic chemicals.

They estimated that, on average, 25% of the aerosols in the Los Angeles basin come from vegetation, which includes an estimated 18 million or more trees.

Plant derived aerosols are likely made of the chemical isoprene — the building block of rubber or plant chemicals such as terpenes, which consist of two or more isoprene building blocks combined to form a more complex molecule. Cohen says that PM2.5 aerosols can be thought of “as little tiny beads of candle wax,” with plant-derived aerosols composed of many molecules of isoprene and terpenes, which are found in pine tree resins.

“I am not suggesting that we get rid of plants, but I want people who are thinking about large-scale planting to pick the right trees,” he said. “They should pick low-emitting trees instead of high-emitting trees.”

The research was described this month in the journal Environmental Science & Technology.

How does global warming affect pollutants?

Cohen, who has studied the temperature dependence of urban ozone levels for insight into the impact climate change will have on pollutants, decided two years ago to investigate the temperature dependence of ozone and aerosol pollution in five counties in the Los Angeles basin: Los Angeles, San Bernardino, Riverside, Orange and Ventura. He and Nussbaumer looked at data from 22 measurement sites across the basin — eight in LA County, two in Orange County, five in Riverside County, four in San Bernardino County, and three in Ventura County — to study aerosols, and at four sites — three in LA, one in San Bernardino — to study ozone.

The researchers found that at the beginning of the 21st century, the relationship between temperature and aerosol pollution was quite varied: if the temperature went up, sometimes PM2.5 concentrations would increase a lot, sometimes a little. Today, the relationship is more linear: If the temperature goes up a degree, PM2.5 concentrations predictably increase by a set amount.

Cohen and Nussbaumer focused primarily on secondary organic aerosols (SOA), which form as particles when gaseous pollutants — primarily nitrogen oxides (NOx) and volatile organic compounds (VOCs) — react with sunlight. The same conditions produce ozone.

Using a simple atmospheric model, they concluded that both regulated chemicals from vehicle exhaust and cooking — primary organic aerosols such as benzene, toluene, ethylbenzene and xylene — and isoprene from plants were precursors of the majority of the organic aerosols observed. Their model suggests that about a quarter of the SOA in the LA Basin are formed by isoprene or other very similar compounds, and that these represent most of the temperature-dependent increase. While there is evidence that some temperature-dependent VOCs have been controlled over time, such as those from evaporation of gasoline, isoprene is not one of them.

Cohen noted that as electric car use increases, the importance of organic aerosols from vegetation will become more dominant, requiring mitigation measures to keep levels within regulatory limits during heat waves.

“Cars are also contributing to ozone, and in the LA basin the ozone level is also high, at high temperatures and for the same reason: There are more organic molecules to drive the chemistry when it is hot ,” Cohen said. “We want some strategy for thinking about which plants might emit fewer hydrocarbons as it gets hot or what other emissions we could control that prevent the formation of aerosols.”

Cohen hopes to look at data from other urban areas, including the San Francisco Bay Area, to see if the temperature-dependent aerosols now dominate, and whether vegetation is the culprit.

The study was funded in part by a grant (NA18OAR4310117) from the National Oceanic and Atmospheric Administration (NOAA). Cohen and Allen Goldstein, a UC Berkeley professor of environmental science, policy and management and of civil and environmental engineering, have also partnered with NOAA scientists and the state and local air quality agencies on an experiment to observe emissions in Los Angeles at different temperatures. Combining these different observing strategies in the LA Basin, Cohen hopes, “will lead to better ideas for reducing high ozone and aerosol events in the basin, ones that can then be used as a guide in other major cities suffering from poor air quality.”


Cohen also maintains a high-density network of 75 pollution monitoring stations around the Bay Area called BEACO2N. Cohen just started a collaboration with William Berelson at the University of Southern California and the Los Angeles Unified School District to deploy BEACO2N nodes in that area of Southern California.

From EurekAlert!

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March 23, 2021 10:09 pm

Life is a terminal disease.

Reply to  Dennis
March 24, 2021 12:03 am

“life is a disease, from which we recover bit by bit” Breyten Breytenbach

Reply to  Dennis
March 24, 2021 6:58 am

Yes, and it’s sexually transmitted.

March 23, 2021 10:20 pm

Makes one wonder how humans ever got started with all those trees around.
No surprise to anyone other than an environmental activist that a raw, untouched by human influence, natural environment is the most dangerous place to be for all living creatures.
A well managed suburban environment now has a far wider variety of plants and creatures than the original landscape.

Reply to  Stephen Wilde
March 24, 2021 2:56 am

Having grown up in So. California I’m surprised there is no mention of the trees I recall were most aromatic, Eucalyptus and Junipers which I think are not native. Guess you’ll need permits to plant trees going forward.

Reply to  Sean
March 24, 2021 4:31 am

If you outlaw trees, only outlaws will have trees.

Russ Wood
Reply to  Scissor
March 27, 2021 5:24 am

South Africa tried to outlaw ‘foreign’ plants some years ago. Then someone finally noticed that the dominant tree (and a beautiful one) in the capital city of Pretoria/Tshwane is the Jacaranda. And that the Jacaranda is a South American ‘invasive species’. And that there are MILLIONS of jacarandas all over the country (there’s one in my front garden). So they gave up!

Reply to  Sean
March 24, 2021 9:57 am

You don’t already?

Reply to  Stephen Wilde
March 24, 2021 7:54 am

29% of San Fransicko’s air pollution comes from China…ozone and particulates from coal burning…..are carried across the Pacific so East Asia is polluting the entire northern Pacific…ironic, no?

Reply to  Anti_griff
March 24, 2021 8:11 am

OK, so what do you suggest we do about it, Griff? Should we ban China? They’ve shown that they don’t put much stock in all this Warming BS, so we probably won’t get very far with that idea!

Reply to  IAMPCBOB
March 24, 2021 8:32 am

BOYCOTT CHINA. CCP is similar to the nazi party.

Reply to  Anti_griff
March 24, 2021 11:18 am

Links I saw articles back to 2010. Obama did nothing about it.



Nancy and Joe will get right on this.

Reply to  Anti_griff
March 24, 2021 2:34 pm

@Griff – This is the first intelligent thing you’ve ever said. Having said that, I am shocked, shocked, that you are criticizing your Chinese masters. Or, are you trying to incite anti-asian violence as an excuse for imposing more draconian laws?

Smart Rock
Reply to  Komeradecube
March 24, 2021 8:12 pm

Apparently, Anti-griff is not griff. Who’d have guessed?

March 23, 2021 10:23 pm

So now all of the forest vegetation must be cleared ? There’s no stopping these terrified bedwetters.

Reply to  Streetcred
March 23, 2021 11:06 pm

No. Just “replanted” with aerosol-free plastic trees and shrubbery! Think of all the money that can be made and the jobs created (as well as water saved) by manufacturing and planting plastic Sequoias and Redwoods. Probably a lot more than painting the streets of LA white. Someone needs to bring this study to Gavin Newsome’s attention. They could probably be made fire-resistant as well.

Another element of the new green economy falls into place!!!

Last edited 18 days ago by Anon
Reply to  Anon
March 24, 2021 8:12 am

Yes, and we can start making those plastic trees using solar and wind power, instead of that nasty petroleum! Yeah, that oughta work REAL well, huh?

Reply to  Anon
March 24, 2021 2:44 pm

How many fire resistant plastics are being manufactured?

Reply to  Streetcred
March 24, 2021 12:15 pm

It will cut down on forest fires. And think of all the wood pellets that could be produced.

Steve Case
March 23, 2021 10:37 pm

….I want people who are thinking about large-scale planting to pick the right trees,…“They should pick low-emitting trees instead of high-emitting trees.”

Cohen noted that as electric car use increases, the importance of organic aerosols from vegetation will become more dominant, requiring mitigation measures to keep levels within regulatory limits during heat waves.

 “We want some strategy for thinking about which plants might emit fewer hydrocarbons as it gets hot or what other emissions we could control that prevent the formation of aerosols.”

Regulators are like Pavlov’s famous dogs salivating at the prospect of creating a whole new class of regulations.  

Reply to  Steve Case
March 24, 2021 2:46 pm

racial profiling of plants?

March 23, 2021 10:55 pm

PM2.5 is generic name for particles with effective diameters of less than 2.5 microns. PM2.5 or aerosols in general are demonized just like carbon dioxide when in fact aerosols have important and significant functions in the natural cycles especially in the hydrologic cycles for its function in the nucleation process of water vapor. Aerosols are also generated from salt sprays. In most cultures, a good deep breath of aerosols from the sea is considered a good remedy for colds and coughs.Sound scientific discussion on aerosol would preferably have a fingerprinting exercise to determine the source and nature of aerosols rather simply demonizing and creating panic.

Steve Case
Reply to  eo
March 23, 2021 11:18 pm

demonizing and creating panic.

“The whole aim of practical politics is to keep the populace alarmed (and hence clamorous to be led to safety) by an endless series of hobgoblins, all of them imaginary.” H.L. Mencken

Reply to  eo
March 24, 2021 1:34 am

The UK government’s Committee on the Medical Effects of Air Pollution (COMEAP) estimate exposure to PM2.5 attributes to 29,000 premature deaths in the UK every year

Ron Long
Reply to  griff
March 24, 2021 3:21 am

griff, another estimate involving “linear with no threshold” thinking, which is not scientific but in widespread political use.

Reply to  Ron Long
March 24, 2021 2:48 pm

But impossible to falsify? The best kind of 21st century science.

Reply to  griff
March 24, 2021 3:55 am

Estimates? Can you name 1, 2. 3 of these people, griff.

If not, crawl back under your toadstool.

And why not a word about all the people who die from particualte and other fumes from dung in third world countries..etc because you and your regressive, people-hating, greenie, anti-CO2 cult members DENY them access to decent reliable electricity.

Oh that’s right YOU DON’T CARE. !

Last edited 18 days ago by fred250
Reply to  griff
March 24, 2021 6:01 am

Full quote:

The current (2008) burden of anthropogenic particulate matter air pollution is, with some simplifying assumptions, an effect on mortality in 2008 equivalent to nearly 29,000 deaths in the UK at typical ages and an associated loss of total population life of 340,000 life-years. The burden can also be represented as a loss of life expectancy from birth of approximately six months.

The uncertainties in these estimates need to be recognised: they could vary from about a sixth to double the figures shown. 

So between 4833 and 58000 people may or may not die 6 months earlier than expected regardless of other aspects of their lives.

In other news, between 550,000 and 600,000 people in the UK will not die of “anthropogenic particulate matter” each year.

Last edited 18 days ago by Redge
Reply to  Redge
March 24, 2021 12:19 pm

Hmmm, the quote states “anthropogenic particulate matter air pollution. Is that ONLY PM2.5, or is that all such air pollution? How about some clarification, griff?

Reply to  Retired_Engineer_Jim
March 24, 2021 3:31 pm

The document Griff didn’t link to so people could easily check his claim states it is 2.5

Reply to  Redge
March 24, 2021 2:54 pm

A fairly long term study done in China was reported here perhaps two years ago. One region used extensive coal burning for home heating and cooking, the other was government forbidden to use any coal. Being done with humans it undoubtedly suffered from lack of precise controls. Anyway, a difference, based on mortality statistics, of several months in life expectancy was found, favoring no coal burning for (a very slightly) longer life.

Reply to  griff
March 24, 2021 8:36 am

If it saves just one life, we should all sacrifice and get all emotional, no?

Reply to  Anti_griff
March 24, 2021 11:48 am

They don’t know whether or not they’d save a single life

Reply to  griff
March 24, 2021 9:20 am


“29,000 premature deaths” are an imaginary statistic. Totally meaningless and it discredits any argument you make by referring to it.

Premature by how much? A day? A month? And relative to what?

In case you haven’t noticed, life expectancy is still going up. And air quality is still improving.

Significant UK air quality improvements over past 40 years cut death rates | UK Centre for Ecology & Hydrology (ceh.ac.uk)

Last edited 18 days ago by ThinkingScientist
Reply to  griff
March 24, 2021 11:26 am

As someone who I would think believes in the theory of evolution, how would the human race NOT have evolved to live breathing all sizes of particulates since the time of mastering the use of fire?

Or are you just anti science? An evolution denier?

Explain yourself Griff!

Reply to  Drake
March 24, 2021 2:57 pm

Can anything that, in general, causes “premature” death after breeding age effect biological evolution?

Reply to  griff
March 24, 2021 11:45 am

You never miss the opportunity to say something stupid

Reply to  griff
March 24, 2021 12:10 pm

Clim-munists can always come up with huge numbers of statistical deaths, but rarely actual death certificates to match. Usually the number is half or double the automobile deaths to add credibility, and come from some official sounding agency nobody has heard of. Obviously if agency A claims there are 40 million climate refugees, then 1.2% of them must die just from old age, OMG that’s half a million a year climate deaths for agency B to seek funding for, using published stats….

Reply to  griff
March 24, 2021 1:21 pm

29000 bodies should be easy to identify so – show me the bodies, griff. I didn’t think so…

Reply to  griff
March 24, 2021 2:38 pm

There ya go, Griffy old boy, back to your usual stupid self. You used up your one intelligent comment for the decade.

Last edited 17 days ago by Komeradecube
Kevin McNeill
March 23, 2021 11:28 pm

Cut em all down make a desert!!

Paul C
Reply to  Kevin McNeill
March 24, 2021 5:13 am

Don’t forget to use fossil fuels to transport the wood just a quarter of the way round the globe to burn in UK powerstations, where it will be classified as carbon neutral fuel. Destroying the trees will also get rid of those larger particulates which are tree pollen. Better get the glyphosate deployed to prevent regrowth. Oh, and those deserts seem to produce dust storms, so will need to be sealed with concrete. Then a whole load of GND jobs created to paint the concrete.
Perhaps just cut enough trees down to create reliable firebreaks and protect property, infrastructure, and power lines instead.

Reply to  Paul C
March 24, 2021 3:06 pm

The results of fire suppression efforts in Southern California, from a USGS long term study — opposite results to expectations

Reply to  Kevin McNeill
March 24, 2021 7:55 am

How about bringing back some of the plant eating animals using DNA extracted from fossils collected at the La Brea Tar Pits?

And just so these animals don’t get out of control, bring back Sabre Tooth Tigers and those gigantic wolves. This would help with social distancing and also help to reduce the homeless problem.

Matthew Bergin
Reply to  Scissor
March 24, 2021 11:51 am

To do that wouldn’t we have to burn enough fossil fuel that the increase in CO2 induced photosynthesis could raise the oxygen levels so those giant herbivores could exist. If true, I could do without the extra large insects that would accompany them. 😱 🤷‍♂️

Peta of Newark
March 23, 2021 11:36 pm

My head hurts reading this Cohen joker….
1) I thought aerosols were water-based. As per when very hydrophilic species like NOx and SOx attract and retain water molecules.
Dunno what the name for bits of soot and candle wax are, apart from ‘particulates’ – hence the letter ‘P’ in PM10. PM2.5 etc

2) We really are in the surreal world of Ozone Hole chemistry when it is asserted that sunlight and VOCs react to create (ground-level) Ozone.

Ozone is a hideously destructive substance )oxidiser) that will destroy VOCs and take itself out of circulation at the same time.
Basically, put something burnable (VOC) in the presence of an oxidiser (Ozone) then add a light/spark (UV from the sun( and you will get water plus CO2.
Not More Ozone

3) Take yourself outside, for a walk where there are living plants, just after sunset.
Smell the air.
There will be/is ‘something’ very aromatic about it. Not any particular thing you recognise, just aromatic and, depending where you are, quite strong.
(I’m next to the remains of Sherwood Forest= very ‘rural’
Forest has not a lot of Oak anymore but lots of Silver Birch and Conifers. It smells strongly)
Repeat your walk just before sunrise.
The smell will be gone

Refer back to point 2 and:

  • Recall Cohen raving about temperature
  • The smell, not obvious daytime, very obvious at sunset, all gone at dawn
  • Ponder, where does Ozone really actually come from, both in the Stratosphere and at ground level. Vitamin D is your entry-level clue/question.
  • What is the main difference between day and night
  • What effect something as ghastly as Ozone might have on living tissue, plant or animal

Lets try put this all together…
My assemblage of those parts says that:
Plants create VOCs, not just ‘for the fun of it’ but to protect themselves against Ozone.

The Ozone is coming from the UV in sunlight (the same UV that makes Vitamin D)
Also sunlight tending to be more visible in daytime than night-time

Strangely also, strange to Cohen it seems, the arrival of Old El Sol up in the sky, ‘makes things warm’ and also the light, not esp the warmth, stimulates the plants to do what it is they do do.

Yes? No?

Plants make and release VOC, during the daytime, to protect themselves from Ozone damage. The Ozone coming from solar UV which is also and only present during daytime. Daytime also – Warm Time

Hence my observations, you can do them too, of Forest Smells

Now it gets crazy.
Because, cars did used to be very leaky things, especially where their fuel was concerned. Petrol/gasoline being an especially VOC
It leaked at filling stations, shonky fuel tanks but mainly from engines burning ‘rich’ fuel mixtures.

All that had to stop, seemingly, so now we take better care of the fuel, have lean burn engines and catalysers to burn off anyfuel that does try to ‘do a runner’

And now we have Ozone problems and Aerosol issues because:

  1. Previously burnt fuel would have taken down the Ozone being (naturally unavoidably) created by El Sol
  2. The lean burn engines run much hotter and thus oxidise Nitrogen. Which combines with water vapour to create, yes they are very unpleasant, Aerosols (tiny drops of nitric acid in reality

Isn’t just such a fantastic buck pass?
They cleaned up the vehicle engines, trying to be rid of actual PM10 and PM2.5
But created another problem in that while the previously leaky engines cleaned up Ozone, they new engines came along producing NOx – almost as bad for your breathing as it is for plantlife as Ozone was/is.
They also thought that ‘better fuel economy’ would reduce pollution so enforced diesel engines. But diesels create huge plume of soot pollution and also NOx
They Made It All Worse

Then The Plants respond to the new threat of NOx aerosols by creating more VOC
(NOx is nebulous stuff, it is in dynamic equilibruim with itself all the time. That equilibrium involves the appearance/disappearance of lots of Oxygen Free Radicals – just like Ozone. Ma Nature neutralizes NOx with water but sadly Nitrous & Nitric Acids are intermediate steps)

Enter Cohen the Clown with The Buck Pass to blame it all on the plants.
Perfectly contrived chemical garbage complete with Cause Effect reversals and all relying on A Computer for its authority

What’s stopping you Cohen. Just cut burn slash poison plough drown bury the things, as is being done all around this insane world right now – huge amounts of it in the lunatic idea that we will be ‘saved’ by doing so. Saved from what exactly?
That’s what you’re saying, destroy the plants.
OK. Pull the trigger. Destroy the plants and the planet and effectively, put us all out of your imaginary misery.
You haven’t got the guts though have you – you are a total, pathetic, Biden-voting douche-bag wimp, hence the need for A Computer.

Cohen, You and The Perpetrators of Climate Change Could Not Be More Wrong.
About Everything.

Last edited 18 days ago by Peta of Newark
Reply to  Peta of Newark
March 24, 2021 3:10 pm

Chemistry isn’t a philosophy.

Reply to  AndyHce
March 24, 2021 4:04 pm

I gave you an up vote but I have to disagree. By definition, my highest degree in chemistry says doctor of philosophy.

Reply to  Scissor
March 24, 2021 7:18 pm

Labels are not reality. I think you probably understand that I meant: however flawed vis a vis the real world, opinions can carry considerable social weight, at least within a group, but chemical reactions are the same regardless of anyone’s beliefs.

March 24, 2021 12:15 am

So, first Frauci got his knickers in a knot because we filthy scum actually touch animals, so he wants to ban all human-animal interaction. Then he banned human-human interaction, leaving granma to rot in solitary neglect in some institution where she can earn the Good Doctors (9+19+39) $67 000 by cathcing covidiocy.
Now we are not allowed to go near plants?
Strange how all the mad gunmen go shoot up little kids and supermarkets, but somehow Baal Gates and Frauci can party safely with the Epsteins, Clintons, Adelsons and Bushes, with nobody taking pot shots at them…
Then again, I don’t really know how things go at a Gates party, apparently that is “too gruesome for public revelation”, or what was that Maxwell judgement again?

Reply to  paranoid goy
March 24, 2021 8:03 am

Illegal aliens pouring into the country wear Joey Biden T-shirts but no masks…Joey sez come on aboard and Fauci sez NOTHING.

March 24, 2021 12:20 am

I think they have forgotten the natural climate needs aerosols to increase cloud formation and precipitation? That’s partly why we get more rain events after big years of bushfires. The other part of the process is needing cosmic radiation which is reduced when the sun is more active (more sun spots, more solar flares). There are natural emissions & cycles they don’t understand in their “simple” models.

March 24, 2021 1:03 am

Twenty years ago, just about every day in LA was in violation of a health-based standard. And now it is only the hot days.

So, should LA face fines for those violations of the law? That quote exposes a mindset that is scary. People who think like that should be gently pried from the levers of power and placed somewhere they can’t harm the rest of us.

March 24, 2021 1:05 am

So, let me get this straight. There are regulatory limits on nature?

Reply to  Davidf
March 24, 2021 6:16 am

Where’s the tree hugger folks now?

Reply to  John Shewchuk
March 24, 2021 12:27 pm

Well, the bird lovers (e.g., Audubon Society) don’t care about wind famrs killing birds, so why should tree huggers care about cutting down all the trees? Its to save the Planet.

Shanghai Dan
Reply to  Davidf
March 24, 2021 12:39 pm

Well, we’ve finished regulating human nature, time to get to the rest of it…

Reply to  Davidf
March 24, 2021 3:20 pm

I don’t know about outcomes but there were some articles a few years back about the EPA trying to fine (Oregon or Washington?) over the fact that ozone levels were higher than statutory limits in some “wilderness” areas. Those ozone levels were due to sun light and tree chemistry.

March 24, 2021 3:16 am

So it turns out that Mother Nature is a nasty bitch! Every spring she begins pollute the air and my windshield with pollen. It’s everywhere! We all need to run our gasoline engines as much as possible so that the engine air filter can filter out as much pollen as possible. Mother Nature is such a nasty bitch!

Reply to  eyesonu
March 24, 2021 7:20 pm

Are your air filters cost effective in relationship to the wide world (rather than just for the health of the engine)?

Last edited 17 days ago by AndyHce
A C Osborn
March 24, 2021 3:27 am

Actual on the ground studies, as against computer modelling have shown that Particualtes are mostly from Tyre Dust, Brake Dust, Cement Dust and in Northern climes Wood Burning stoves.

Reply to  A C Osborn
March 24, 2021 5:57 am

What you’re saying is true but that’s not what they’re talking about.

There are actual measurements of what’s in the air and some of that is organic chemicals. The question is about the source of those chemicals. The measurements show that the concentration of organic chemicals is temperature dependent. The researchers say that eliminates the possibility that household cleaning products are the source.

Some kinds of trees are heavy emitters of the kind of chemicals they’re measuring and the emissions are temperature dependent. It’s not 100% proof that it’s the trees but it does sound like household chemicals are off the hook.

What else could it be? How about nematode flatulence? How about decomposing algae?

Reply to  commieBob
March 24, 2021 2:42 pm

Heavy is a relative term. What is the correct level of natural aerosols and who determines it? Probably the same individual responsible for picking the best global temperature.

March 24, 2021 3:59 am

Yet in spite of all this doom and gloom the average lifespan in the world has risen from 33 years to 70 years since 1900.
The only pity is the extra years are at the end of life, whereas some extra years in one’s 30s would have been more fun.

Reply to  StephenP
March 24, 2021 4:27 am

I think you get them. As far as I can tell, we’re not only living longer but we’re staying healthy longer.

Reply to  commieBob
March 24, 2021 6:18 am

And that is another problem caused by global warming.

Reply to  StephenP
March 24, 2021 10:49 am

I think living longer while parked in a wheelchair in front of a TV set in a group home and having non relatives from foreign countries wipe your butt and drool is a desirable way to spend all those extra years of life we are now getting, don’t you?

Reply to  StephenP
March 24, 2021 7:30 pm

Based on a paper I read in the 1980’s, using all the data from the earliest U. S. census to the (then) present, it all depends on the end points. Looking at the entire population, which means counting all those once common infant deaths, the average life span had indeed increased rather a lot. However, considering only those people 60 and older, there had been no change what so ever in life span.

I have not seen any studies, or even wild claims, since then that looked at the data in the same way.

March 24, 2021 4:00 am

Fine, cut down all the trees, problem solved.

Bruce Cobb
March 24, 2021 4:43 am

Stupid trees and plants spewing all their nasty aerosols and pollen pollution. Hey, I know, let’s get busy removing the CO2 they depend on, thus “tackling climate” and plants together. Win-win!

March 24, 2021 5:53 am

Behold a new narrative….

 …the most concerning source of dangerous aerosol pollution may well be trees and other green plants…

Which follows on from the bombshell news that…

Amazon rainforest ‘now making climate change WORSE’ and is ‘warming Earth’s atmosphere’, study claims


Gosh. Vegans are the new pariahs!

Rich Lambert
March 24, 2021 6:03 am

The solutions is obvious. California needs a vegetation tax.

Reply to  Rich Lambert
March 24, 2021 6:20 am

Finally, now we have absolute proof that humans have altered the climate.

March 24, 2021 6:10 am

From the post: “Aerosols — particles of hydrocarbons referred to as PM2.5 because they are smaller than 2.5 microns in diameter and easily lodge in the lungs — are proven to cause cardiovascular and respiratory problems.”

I don’t believe this is true. Steve Milloy has done much work on this and “proven” is not word that can be found in the literature.

But this post does point to maybe President Reagan was correct.

Charles Higley
March 24, 2021 6:18 am

Aerosols — particles of hydrocarbons referred to as PM2.5 because they are smaller than 2.5 microns in diameter and easily lodge in the lungs — are proven to cause cardiovascular and respiratory problems.”

No, it has not been proven. A few years ago, the EPA tried to prove it and gave subjects 60+ times what was the limit, expecting them to die and no one did. One woman got nauseous. This study was a bust and they buried the results.

As isoprenoid compounds from plants are completely natural, we, as a species, are very used to them and should not be seriously effected. They are high only during bad spells and it would be stupid to get rid of some or all of the plants.

Oddly, here, I was not allowed to mention “i.s.o.p.r.e.n.e.” in this post—it keeps getting deleted. This is not a spellchecker, it is censorship. This needs fixing.

Reply to  Charles Higley
March 24, 2021 2:08 pm

I thought that the EPA had said that they couldn’t have any proof of their contention that PM2.5 was harmful because to subject humans to PM2.5, something they considered to be harmful to health, would be against the agencies ethics. Can you provide a reference to the test and results? Or has that data disappeared?

March 24, 2021 6:55 am

So, all of the recent California forest fires were actually part of their pollution abatement program?

Gordon A. Dressler
March 24, 2021 7:02 am

Obviously, it’s way past time for a carbon tax on owning trees and other green plants.

A big “thank you” to the geniuses at UC Berkeley for pointing this out.

Reply to  Gordon A. Dressler
March 24, 2021 7:35 pm

I’ve read complains from various places around the country that local zoning law have outlawed home vegetable gardens.

Reply to  AndyHce
March 25, 2021 3:43 am

Leftists do not want people growing their own food.

Robert of Texas
March 24, 2021 7:32 am

That’s it…the California AG should sue the trees immediately. They should be listed as polluters and regulated by the EPA. May little smoke stacks with filtration can be installed on each one; that or sequester all gases they emit deep into the ground. Maybe would could start a “Plant Tax” to help pay for all of this.

Reply to  Robert of Texas
March 24, 2021 8:08 am


March 24, 2021 8:30 am

Cut them down, cut them all down.
Saruman (leader of the climate wizards)

Michael E McHenry
March 24, 2021 8:32 am

Lets not forget about those termites who are responsible for 10 percent of methane emissions. Haven’t they heard of global warming?

March 24, 2021 9:56 am

They should plant more mechanical trees, then they won’t have this problem.

March 24, 2021 11:21 am

Ronald Reagan mentioned this once and people heaped scorn on him for months (years). James Brady ran through the press plane yelling “Killer Trees!”

March 24, 2021 11:34 am

It can’t possibly need to be said that trees do not produce dangerous aerosols……they do produce lots of aromatic aerosols — anyone ever walk in a pine forest on a hoit summer day, say up in Big Bear or Lake Arrowhead? The falsehood here is that they are “dangerous”.

Jon Salmi
Reply to  Kip Hansen
March 24, 2021 12:02 pm

From a 2017 study:

Monoterpene emissions from needles of hybrid larch F1 (Larix gmelinii var. japonica x Larix Kaempferi) grown under elevated carbon dioxide and ozone:
  PR Mochizuki, Watanabe, Koike & Tani in AE; January 2017
  “Total monoterpene emission rate decreased by 36% in response to elevated CO2 when compared 
  with control (P < 0.05).”
  See http://www.sciencedirect.com/science/article/pii/S1352231016308482
  See also http://www.co2science.org/articles/V20/jan/a8.php
Monoterpenes constitute a major fraction of the biogenic volatile organic compounds or BVOCs given off by plants. From a climatic perspective their emissions are important because they contribute to the formation of photochemical oxidants (e.g., ozone) and are thought by some to represent a positive feedback to global warming (Boucher et al., 2013).
Introducing their contribution to the subject, Mochizuki et al. (2017) write that “to estimate the effect of monoterpenes emitted from larch species on the atmospheric chemistry of the northeastern Eurasian continent in the present and foreseeable future, it is necessary to investigate how emissions and composition of monoterpenes emitted from larch species vary against climate change.” Thus, the four Japanese researchers designed an experiment to investigate the effects of CO2 and ozone (O3), both alone and in combination, on monoterpene emissions from the hybrid larch F1 (Larix gmelinii var. japonica x Larix Kaempferi). More specifically, they grew 2-year-old seedlings in open-top chambers, subjecting them to control or elevated CO2 (380 ppm control, 600 ppm elevated) and/or O3 (<6 nmol mol-1 control, 60 nmol mol-1 elevated) concentrations during the daylight hours of two growing seasons, measuring their monoterpene emissions from 5-cm-long shoots.
So what did their experiment reveal?
Mochizuki et al. report that” total monoterpene emission rate decreased by 36% in response to elevated CO2 when compared with control (P < 0.05).” In the combined elevated CO2 x O3 treatment total monoterpene emissions also declined, and by nearly the same amount (32%), whereas it experienced a nonsignificant 23% increase in the elevated O3 treatment.
In light of the above findings, the negative effect of elevated CO2 on total monoterpene emissions observed in the saplings of the hybrid larch F1 should be welcomed by those concerned about future global warming for its potential to mitigate some of that warming.

I also remember reading at that time, that the Great Smoky Mountains and the Blue Ridge Mountains get their names from the aerosol haze of the monoterpenes.

Reply to  Jon Salmi
March 24, 2021 1:02 pm

Jon ==> Yes, the Great Smoky ountains are smokey due to VOCs: “VOCs are chemicals that have a high vapor pressure, which means that they can easily form vapors at room temperature. The millions of trees, bushes, and other plants in the Great Smoky Mountains all give off vapor, which comes together to create the fog that gives the mountains their signature smoky look.”

John F Hultquist
Reply to  Jon Salmi
March 24, 2021 10:07 pm

Author(s) seem to be from California.
I wonder if they know of the Blue Ridge Mountains and the Great Smoky Mountains National Park? The Blue Ridge Parkway is worth a bit of your time, and quite not like the Arroyo Seco Parkway in the LA area.  

Reply to  Kip Hansen
March 24, 2021 7:44 pm

Plants, particularly trees, have long been claimed to be the cause of the hazy air in place like Tennessee’s Great Smokey Mountains and the Appalachian’s Blue Ridge Mountains. I don’t recall the exact translation but the LA Basin was called something like “Smokey Valley” by the natives at the time the Spanish first arrived.

Reply to  AndyHce
March 24, 2021 8:39 pm

Pesky trees..
The Blue Mountains, west of Sydney, appear blue due to emissions from eucalypts…

Get rid of vegetation [regress to a pre-Devonian lifescape] and get rid of monoterpenes

Reply to  GregK
March 25, 2021 3:45 am

The Smoky Mountains. They aren’t called that because they are on fire!

March 24, 2021 12:14 pm

“Aerosols — particles of hydrocarbons referred to as PM2.5 because they are smaller than 2.5 microns in diameter and easily lodge in the lungs — are proven to cause cardiovascular and respiratory problems.”
I thought that the EPA had no data on the effect of PM2.5 on humans, as they couldn’t conduct any tests because of the ethical implications of subjecting people to such deadly particles. So, how has it been PROVEN that PM2.5 cause cardiovascular and pulmonary problems?

Steve Z
March 24, 2021 12:29 pm

Well if isoprene from trees causes cancer, don’t worry, dogs can cure it! Just ask Joe Biden!

But even if some trees emit isoprene, let’s not cut them down–we still need the oxygen they put into the air!

Joel Patterson
March 24, 2021 1:54 pm

Silly article. The only time trees pollute is when there’s a forest fire.

March 24, 2021 2:11 pm

I sometimes wonder how much of the supposed “global warming” since the 1960s, is due to the various Clean Air Acts that were implemented around the world in the mid/late-20th century.

Loren C. Wilson
March 24, 2021 5:45 pm

Toluene is not a carcinogen. My industrial hygienist liked to complain about it in the lab but had to acknowledge that toluene has never been shown to have carcinogenic properties unlike its close cousin benzene. It is classified as a suspected carcinogen although it has never been convicted even though hundreds of studies have been performed.

Hurricane Willy
Reply to  Loren C. Wilson
March 25, 2021 8:00 am

Benzene + vitamin C = highly carcinogenic. Check your sun screen, the skin cancer epidemic was never down to “holes in the ozone”. That one was a test to see how scientifically illiterate the masses are before they went full bore on the AGW.

Hurricane Willy
March 25, 2021 6:24 am

Stopped reading when I got to “The researchers found that at the beginning of the 21st century, the relationship between temperature and aerosol pollution was quite varied: if the temperature went up, sometimes PM2.5 concentrations would increase a lot, sometimes a little. Today, the relationship is more linear: If the temperature goes up a degree, PM2.5 concentrations predictably increase by a set amount”

Last edited 17 days ago by Hurricane Willy
Roger Taguchi
March 25, 2021 7:00 pm

Anyone measure ozone produced by arcing in electric motors? E.g. from electric cars.

March 26, 2021 8:51 am

Tony Villar, the previous mayor of Los Angeles, had as his primary initiative against pollution the goal of planting 1 million new trees throughout the city. As with all govt programs this one was marginally successful, there were about 100+ thousand trees planted by the time he left office after two terms. One wonders what he may think of this should he ever read this study.

Nan G
March 26, 2021 12:56 pm

I never suffered from plant allergies until I left CA, where I had plenty of smog related breathing issues growing up.
Plants, trees, really do fill the air with irritating stuff.
Unintended consequences are always interesting to watch.
Now I hear CA might cover all their miles of canals with solar panels.
Surely there are quite a few unintended consequences they haven’t thought about if they follow thru.
The heat on the water will evaporate lots more than the mere sunlinght had.
The rotting plant life will cost more to clean out of water for drinking.
And, even nowadays, solar energy does not store well leading to fluctuations in power use from other sources to balance it.

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