Trinity Nuclear Test

Bosque del Apache National Wildlife Refuge

near San Antonio, New Mexico

On July 16, 1945, the first atomic bomb test was performed at a site about 35 southeast of Soccorro, New Mexico.  The test was code named 'Trinity' by Dr Robert Oppenheimer, director of the Los Alamos Laboratory involved in the Manhattan Project.  It used a 20 kiloton Plutonium implosion device, of a similar design to what would ultimately be dropped over Nagasaki on August 9, 1945, less than a month later.  The Manhattan Project was a war-time effort to develop an atomic bomb, which occurred over a time period from 1942 to 1946.  The effort extended to a number of facilities, including Hanford, Washington and Oak Ridge, Tennessee in addition to the Los Alamos, New Mexico  site where major design work occurred.  Ultimately testing would be done in a number of areas, including Nevada and the Pacific Islands, including Bikini Atoll, after World War II.

The Trinity test differed in nature from that used on the first atomic blast at Hiroshima.  The Hiroshima blast used a gun type, or projectile type detonation of uranium while the Nagasaki and Trinity Blast involved implosion of a plutonium core.

The Trinity atomic bomb test followed a period of development of nuclear expertise in a number of areas, from study of the atom itself, to study of high energy collisions and the study of nuclear chain reactions. A key development was a letter by physicists Eugene Szilard  and Albert Einstein,   expressing their concern that Germany could develop an atomic bomb.  The result of their efforts, which included collaborations with other physicists such as Eugene Wigner and Edward Teller , was that President Franklin Delano Roosevelt accelerated scientific research with a new committee on June 28, 1941 and approved the atomic program on October 9, 1941.  The response to their letter came on October 19, 1941.

This timeline is interesting, taken in the context of the historical evolution, from World War I, in 1914-1918 to World War II and its aftermath in the nuclear arms race.  The historical context included the 1918 Flu Pandemic (Spanish Flu), aided by a World War I fought in the trenches, the Great Depression,  and the ever continuing battle between commercialization, globalization and nationalist interests.  The development of nuclear weapons ratcheted up the stakes, due to the wider implications of their use and the attendant risks.

Nuclear risks include the potential manufacture, storage, transportation, testing and potential use of nuclear weapons in conflict (including WWII).  These risks are in addition to risks arising from nuclear usages in other areas, such as power generation and medical usages.  We have seen impacts from the Three Mile Island, Chernobyl and Fukushima nuclear power plant incidents.  I've discussed some of these issues in other blog articles, including: Nuclear Balance of Risks, Chernobyl 25th Anniversary and Energy Choices and Risk.

Development, testing and use of nuclear weapons has left a long lasting radiological footprint on the landscape in areas such as Hanford and the Pacific Northwest, the Trinity Site and White Sands and the Southwest, the Pacific Islands, including Japan during WWII, and downwind (and water) areas.

The above photograph is taken at Bosque Del Apache National Wildlife Refuge, near San Antonio, New Mexico in February, 2009, about 20 -30 miles from the Trinity Test Site, some 63-64 years after the test.  Another image, taken at Valley of the Fires State Park, New Mexico, was taken near Carrizozo, New Mexico, one of the areas harder hit by the Trinity plume.

The Odd Couple: The Mitochondria and the Cell Nucleus

Mitochondrion (Creative Image)

Mitochondria are key to understanding many life processes, in the body, in nature,
and in our environment.

Years ago, the Eukaryotic cell   developed as a symbiotic relationship between a prokaryotic cell and a proteobacteria.  The prokaryotic cell may have been an archaea. The proteobacteria was was incorporated into the cell as an endosymbiont.  As gene transfer took place between mitochondrial DNA  and the cell's nuclear DNA, the extent of the  mitochondrial DNA (mtDNA) decreased and the nuclear DNA incorporated more of the functions performed previously by mitochondrial DNA.  As this occured, the relationship changed from being symbiotic to the development of the mitochondrion as an organelle within the cell.

Much of the work developing the theory of symbiogenesis was done by Lynn Margulis in a 1967 paper..  The theory behind symbiogenesis is a very important topic with wide ranging implications due to the complexities involved in the interoperablity of nuclear DNA and mitochondrial DNA.  These issues are ongoing and represent a major challenge in understanding a wide range of scientific issues confronting our society today.

Mitochondria are present in most living cells that include DNA.  Mitochondria are responsible for  a large portion of the energy generated by the cell.  Mitochondria are responsible for the generation of adenosine triphosphate (ATP) from adenosine diphosphate (ADP)  through aerobic processes using its electron transport chain (ETC).  The energy generated as ATP is many times greater than the energy generated through anaerboic glycolysis, which is an energy generation process that does not use oxygen.

The use by the cell of anaerobic  vs aerobic respiration has significance in studying various physiological processes which occur throughout the body.  These issues have implications in wide ranging areas from cancer to the relationship between sleep and wakefulness.

As energy is generated throughout the body, principles of conservation of energy must be satisfied.  Whether energy is generated through aerobic respiration and Oxidative Phosphoylation (OXPHOS)  using the mitochondrial electron transport chain (ETC), energy generation requires inputs and outputs that must be balanced.  This is a principle called "conservation of energy".  OXPHOS generates ATP,  the "energy equivalent of currency" in the body, energy in the form of heat, and outputs such as oxygen radicals (Reactive Oxygen Species (ROS))  as a byproduct of the process.

Oxygen Canisters

Oxygen reactive species such as superoxide (O-), hydrogen peroxide (H202) and the hydroxyl radical (OH-) can be generated depending upon a number of factors.   This includes natural process in the body involving signaling and homeostasis and also exposure to a number of environmental factors which may increase their generation.  Antioxidants may help the cell counter some of the impacts of reactive species.

Exposure to pollution, chemicals, toxins and radiation may increase oxygen reactive species exposure.  Radiation exposure may include ionizing radiation or non-ionizing radiation  such as cosmic rays  (e.g. gamma rays ).  Geomagnetic storms  and reduced ozone layer  protection at polar regions as Antarctica and the Arctic may increase such exposure, with greater historical ozone depletion  over the Antarctic.

I photographed in Antarctica in November/December 2004, and in October 2006 and photographed in the Arctic in July 2005.  The year 2006 saw the worst levels of depletion (2004 Image-Halley Bay Station, Antarctica) in recorded history.

Cellular processes guide apoptosis, or programmed cell death under a number of circumstances, generating  an intrinsic pathway or extrinsic pathway for cell death.  Reactive species play key roles in this process, as signaling mechanisms, and also in promoting cell death, as free radicals generated by a variety of situations trigger apoptosis.

Mitochondria play a large role in enforcing 'group identity' in a cell. The mitochondria helps to sustain certain energy needs within the body and when certain system parameters (group identity system requirements) are not fulfilled, the process of apoptosis or programmed cell death is intended to kill off certain cells that do not meet those system parameters.

Mitochondria can be loosely or tightly coupled; this means that they can "leak" protons so that more heat is produced (uncoupled) relative to amount of ATP produced;  there are certain uncoupling proteins  that aid in this process, which decreases  the generation of potentially damaging oxygen radicals.  A highly coupled system will thus be more efficient in the generation of energy, less efficient in generating heat, and will generate more oxygen radicals, which can cause damage to the system.  A more loosely coupled system will produce more heat, will generate less oxygen radicals, and will be less efficient in generating energy.  A loosely coupled system will be more valuable in colder climates due to the greater heat protection.  A tightly coupled one will result in more conditions, such as diabetes, which are impacted by the generation of oxygen reactive species.

The generation of reactive oxygen species is a significant issue in DNA damage  and mutations involving mutagenesis.  Mitochondrial DNA (mtDNA) are much less protected from the generation of reactive species than nuclear DNA.  In the proverbial sense, they sit at the edge of the  oxidative phosphorylation 'fiery furnace' and absorb more damage than nuclear DNA.  Nuclear DNA has greater protection from reactive species, being protected by histones   and telomeres.

Mitochondria can be damaged by reactive species, however, there is a certain amount of punishment that mitochondria can take before a process called heteroplasmy  takes place. Heteroplasmy in the mitochondria is a process where, due to mutation, mitochondrial damage or other process, more than one mitochondrial genome can exist.  This process may be associated with mitochondrial disease and be more extensive the greater the degree of heteroplasmy.  However some individuals may live to long ages with some degree of heteroplasmy.

There is a basic problem with mitochondrial damage and mutation in so far as the mtDNA and the nuclear DNA interoperate in the OXPHOS process.  This is because, as mentioned earlier in the article, some mitochondrial functions ages ago were shifted into the nuclear DNA through the process of gene transfer.  Cytochrome C belongs to the cytochrome c family of proteins and is an integral part of the ETC.  Cytochrome C has a long history, which goes back to time periods when the Earth was subject to heavy amounts of radiation.  Illnesses associated with Cytochrome C may involve both nuclear DNA and mitochondrial DNA.

Since Nuclear DNA has greater protection than mitochondrial DNA (mtDNA) from the insult of reactive species, the degree of damage in each case will differ, or in the case of nuclear DNA, there may be minimal or no damage.  This will lead to interoperability issues as mutations and damage occurs. Interoperability is the ability of systems to work together.  As oxidative stress occurs at different rates and to different but  inter-operating parts of the cell (mtDNA and nuclear DNA), illness and damage occurs, and potentially mutations.  This occurs in systems requiring heavier use of energy, including muscles.  Respiratory muscles bear the burden of oxidative stress, as these muscles are those subject to the greatest use during sleep.  Sleep apnea may be associated with higher levels of exposure to oxidative stress.

As we are subject to greater and greater levels of substances that create oxygen reactive species, we can see that problems can add up.  There are greater and greater chances of damage and mutations, the probability of heteroplasmy increases, the levels of heteroplasmy in the cell may come closer to the levels of heteroplasmy that may be tolerated in the cell without incurring mitochondrial disease.

We can see, therefore, that exposure to reactive species such as environmental toxins and radiation may provide for mutations in both nuclear and mitochondrial DNA, that these processes may occur at different rates, and that past a certain point, mitochondrial disorders may develop as the result of such exposure. At the same time, mutations that are beneficial may sometimes occur, and mutations and damage that are harmful may indeed result.  The ability for mutations that are adaptive to occur may reflect the ability of the mitochondrial DNA and the nuclear DNA to inter-operate, which is statistically difficult, considering the conditions under which each of these processes work.

Thus any process which seeks to advance a species by introducing mutagenic factors via the use of the creation of oxygen radicals must take into consideration that mutations and damage may result in the process and that individuals may be harmed in such process.  Due consideration must exist for who is subject to such exposure, and when the risk of subjecting certain individuals to such exposure constitutes a material risk that makes such experimentation untenable in  a civilized society.

 The risks of exposure to reactive species increases with the degree and length of the exposure, impacting the risk of early morbidity and mortality. Mutagenesis is more effective when it occurs in germ line cells which can pass mutations, either favorable, or unfavorable on to the next generation

Where such experiments are conducted, they must be conducted in an ethical fashion, they must be done with full informed consent of those involved, they must adhere to the law of civilized nations, and the ongoing experience of such studies must be monitored and measured so that those involved are not unduly harmed and the patient population put at excessive risk.

It must be made abundantly clear that if our society depends upon mutations to adapt the species to future environmental (or other) challenges, that those who have been subject to environmental (or other) assaults for such purpose be treated with due respect, that their contributions be valued, and their condition be measured, monitored and treated. It is clear that what these individuals are doing on a collective basis is aiding the future development of humanity. They are test subjects in a process that will benefit others, later.

What are our future ecological and planetary challenges and how can we adapt to them?  How do these challenges impact our exposure to environment risks and how we deal with them?  These are all important issues.

The mitochondria, as a vital cog in the production of energy has a very important part of the story that must be told as we seek to deal with the environment, climate change and other planetary challenges that we face.

Leptin

Butter

I attended a lecture in 2008 about leptin signaling given at Harborview Medical Center through their research programs on diabetes, metabolism and obesity.  The lecture, although highly technical, was  interesting and it gave me plenty to think and read about.

Leptin is what is called a signal transducer.  A signal transducer is an extracellular  signaling molecule that activates a receptor inside or on the cell surface, initiating a series of events, biochemical reactions.    Leptin signaling is involved in a number of areas relating to the management of energy throughout the body, regulating or giving permission for the use of energy for a variety of vital functions.  As I read more about leptin, it led me into a labyrinth of other, associated issues.

Leptin is involved in signaling relating to mesolimbic (dopaminergic) reward centers, food, satisfaction, glycemic control, saiety and reproduction.  Leptin deals with long term energy storage, provision of energy to the brain and gives permission for the use of energy falling within its defined duties.  Intuitively, one wonders what happens if energy demands are requested for things that aren't associated with its associated duties.

Leptin acts to communicate to the Central Nervous System the availability of energy stores.  It acts to restrain food intake and induce energy expenditure, when necessary.   Leptin acts with other systems, such as the Sympathetic Nervous System,  and with factors such as thyroid hormone  and insulin,  in regulating energy use throughout the body and in insuring the thermodynamic  efficiency of skeletal muscle, for example.  Leptin is also involved involved in the cardiovascular system, for example in cardiac hypertrophy.

Leptin is increased, or up-regulated, in obese people.  It increases appetite, generates a low metabolic rate, decreases thyroid function and is impacted by sleep apnea  issues.  Dysregulation of leptin adversely impacts fertility.  Leptin acts on lipid and glucose metabolism.  Leptin also regulates bone metabolism.  This may serve to improve structure with increasing weight by regulating the allocation of higher density bone development.    Leptin resistance occurs during obesity when increasing leptin levels do not have an impact.

Leptin acts in the brain in a neuroprotective  fashion that may also impact memory.  Leptin may be necessary to protect the cell against cell death (apoptosis).

Leptin plays a key role in thermoregulation, working through diverse systems such as the brain's preoptic area and hypothalamus.  Studies in the brown adipose tissue (BAT)  of mice injected by virus indicated involvement of leptin in regulating BAT circuits.  Severely obese mice that lack leptin or its receptor show decreased BAT thermogenesis, and are thus challenged to maintain their body temperature and adapt to cold temperatures.

Leptin may be a key component in considering survival issues under a variety of scenarios or projections associated with climate change modeling.  It may react to a variety of seasonal (zeitgeber) cues, as well as sexual cues regarding melatonin , odor and reproduction.  It will react to hedonistic feelings regarding food, appetite and to the allocation of resources regarding shorter term versus longer term energy needs.

Leptin plays its role along with a host of other players in this complicated web of life.

Book Review:
Group Immunity Systems

 "From Bacteria to Belief: Immunity and Security by Dr Luis P. Villarreal, UC Irvine
in "Natural Security, A Darwinian Approach to a Dangerous World"
edited by by Raphael D Sagarin and Terence Taylor

Fractal Julia Design (creative digit image)

I attended a guest lecture by Dr Luis Villarreal, University of California, Irvine, given at the University of Washington . Dr Villarreal gave a very interesting talk about viruses, which got me interested in reading some of his work on the role of viral evolution in life.

Dr Villarreal's work appears in,  "Natural Security, A Darwinian Approach to a Dangerous World" Edited by Raphael D Sagarin and Terence Taylor.  The book discusses applications of security systems which exist in  evolutionary biology,  to solve security based problems in the risky world that we humans have to deal with.  In this blog post I discuss Dr Villarreal's article, in which he discusses immunity systems.  

Dr Villarreal develops his concept of group immunity based on bacterial models, discussing the colonization of genetic parasites such as viruses.  Systems bind individual units to the group using a "carrot or stick" approach to enforce group identity.   His model employs the term Addiction Model for this approach.  This model uses the term "antitoxin" for protective aspects of the system which draw and retain members, and "toxin" for aspects which are destructive or harmful to nonmembers or members who violate the group identity system rules. Together these aspects constitute a security system which is the basis for his discussion.

Biological based concepts are extended to higher level human biological models by asking how we identify members of a group, how we identify self versus foreign entities and how we respond to threats. Human cognitive sensory systems using visual or pheromone based cues are employed.   

Dr Villarreal tackles the very difficult topic of death of the individual for the good of the whole in the context of programmed cell death (apoptosis) where many cells must die in the process of developing a specific specialized tissue, giving specific biological-based examples.   He discusses the issue of genetic parasites which create an addiction state within a host cell whereby the host cannot lose the parasite and still remain alive.  Competition between group identity systems is also important as Dr Villarreal discusses how group identity systems may kill off individual E. Coli cells if one of them is co-opted by another organism.   

Dr Villarreal goes on to discuss adaptive immune systems.  He discusses the worm C. Elegans, whose neural system and ability to protect against endogenous retroviruses is of evolutionary interest.  He discusses the recognition of self versus foreign, the reigning in of an over-reactive immune system that erroneously attacks itself,and the development and training of group identity.  He discusses how evolutionary features of the immune system can be extended to the social activity of humans based on long standing biological evolutionary principles.

Dr Villarreal discusses the creation of a stable group identity system using sensory based systems that may exclude input from non-members.   "Colonization" and imprinting (of language or group identity) is described as a process through which group identity is established and maintained.  The assignment of meanings to words, through language, and the stability of memories are important in such systems.

Dr Villarreal's work is an interesting discussion of the use of evolutionary biology techniques applied to the phylogenetic "tree of life" and one is left wondering the extant implications for the "tree of the garden of good and evil".  

"Natural Security, A Darwinian Approach to a Dangerous World" can be found  through the California Scholarship Online and on Amazon, with interesting contributions from a variety of authors on the topic of natural security and biological based models.

Fractals 

Portion of a Mandelbrot Set

A fractal is an entity that exhibits a repeating pattern.  Many patterns in nature exhibit fractal phenomenon and computer simulations are used to generate fractal patterns artificially.  Natural phenomena such as coastlines  exhibit a fractal pattern, as the pattern displayed may be exact (self-similar) or perhaps just similar at various levels of detail or magnification.  Snowflakes and trees property of continuing detail at higher levels of magnification.  Because of this, fractals are considered "nowhere differentiable" because of their inability to be measured traditionally.

Fractals are used in many fields, including physics, biology, medicine and physiology, imaging and financial fields. Fractals may apply in economic contexts such as the stock market Standard and Poors 500 Index, when examining longer term patterns (years) vs shorter terms (months, days, intra-day trading).  Fractals may be used in cinema, advertising, graphic design and climate science .  Fractals are a beautiful representation of art in their own way, in the visual arts, including the Droste effect, which is a picture within a picture. 

Fibonacci numbers, the basis of the Fibonacci Sequence appears in fractal geometry in a wide variety of ways.  Fractal dimension is a measure used to quantify complexity.  It measures  how detail changes with scale and the capacity of the fractal to fill space.  Various definitions of fractals and mathematical indicators exist, including a definition by mathematician Benoit Mandelbrot  who characterized a fractal as an object whose Hausdorff-Besicovitch dimension  is greater than its topological dimension. 

Wikipedia lists the Hausdorff-Besicovitch dimensions of a number of common fractals, including the Koch snowflake, Sierpinski Triangle, Quadric Cross, Julia Set and the Boundary of the Mandelbrot Set. Values for natural processes such as  the Coastline of Ireland , Great Britain and Norway are listed, as are values for various Brownian motion and random walk processes.  Dimensions are shown for biological models such as Cauliflower, Broccoli, the surface of the Human Brain , and the Human Lung.  Higher numbers indicate increasing complexity.

Fractals may be use in diagnostic medicine and physiology.  For example, blood vessels may exhibit fractal characteristics, as may the lung and surface of the human brain.  Tortuosity, another metric, relates the ratio of the actual length of a curve or segments of a curve to the distance between the two ends. Tortuosity may also reflect the degree to which a curve crosses over itself.  
  
Tortuosity was used for characterizing animal trails of mites  with regards to Brownian motion pathways.  Fractal dimension and tortuosity may both be used in measurement of blood vessels, as is shown in this article from the medical journal PubMed in a study of pulmonary hypertension.  In that study, distance metric, a measurement of tortuosity, was statistically more significant than the fractal dimension in correlating clinical patient parameters with the particular metric.   This goes to show that the use of different metrics may produce differing correlations, perhaps a clue in itself to underlying characteristic studied.

Fractals  form the basis of many aspects of life and the world around us, igniting our curiosity, aiding our research, informing us, and conveying a sense of beauty, form and function.

The Ginko Biloba Tree

Ginkgo Leaf Fossil, Burke Museum, University of Washington, Seattle, Washington

The above photo of the Ginkgo Leaf Fossil was taken at the Burke Museum, University of Washington, Seattle, Washington and  represents a fossil of a Ginkgo taken in Smithers, British Columbia, Canada.  Driftwood Canyon Provincial Park, in Smithers, is one of the world's most significant fossil beds.   

The Ginkgo Biloba tree appears naturally, in the wild, only in China.  It is grown in many place worldwide, as a cultivated tree, and adapts well in well watered and well drained habitats. Ginkgo Biloba is a living fossil , dating back 270 millions to the Permian Period  .  Ginkgo has managed to evolve along a very long evolutionary time period without much speciation.

It is an interesting example of a plant that has had extreme longevity, slow growth, late reproductive maturity and has survived through many diverse and disturbed environments, including the Ice Age .  It has  managed, despite  a narrow base of speciation to support it.  It has two sexes, male and female, and has its ability to exhibit clonal reproduction, a process which produces a population of identical units which reproduce from the same ancestral line. This has helped it survive evolutionary challenges.  The Ginkgo is also highly resistant to air pollution and grows in areas where air pollution has damaged other species.

A HHMI BioInteractive presentation discusses the issue of clonal reproduction in a video. "Are Males Really Necessary?"  using fruits and vegetables as props.   The video is thought provoking and uses creative use tools to discuss an educational subject.  The 23rd or "sex chromosome"  is a specialized area of interest not explicitly discussed.  Protocols for tossing out wilted lettuce or black bananas present an analytic challenge.

The black banana we consider tossing out might be more useful than the newest banana, especially if we are considering  baking banana bread to bring to the next potluck.  It takes awhile to produce the necessary senescence in a banana to get the right flavor and texture for banana bread.  Thus,  Interoperability, whether it be in bread making, computer engineering or other systems, is an important evolutionary issue, involving mutations along with a stochastic process.

One has to wonder at the combination of processes that has sustained the Ginkgo for million years as well as the diverse environments that the Ginkgo tree  has experienced.   Ginkgo is an herb.  Its leaves and sometimes its seeds are used to make extracts for medicinal purposes, including memory disorders such as Alzheimers and dementia.  Even as we consider the marvel that is the Ginkgo Biloba, we find fascination and beauty in its foliage, and comfort in the shade that it produces.  It is a tree and much more.

World Health Organization Report on Air Pollution and Health

                   Orca Whale, Haze, Strait of Juan de Fuca, British Columbia, 9/18/2012

A report released 3/25/2014 by the World Health Organization attributed one in eight deaths to the impacts from air pollution.   The report indicated that 7 million people died in 2012 as a result of air pollution, making air pollution the greatest single environmental health risk.   The WHO report provides fact sheets on Ambient (Outdoor) Pollution and on Indoor Pollution.   The WHO report displays a number of informative graphical presentations of the world wide distribution and impact of air pollution.  These presentations include the Exposure to Ambient Air Pollution and Mortality from Ambient Air Pollution.

 As the WHO graphs show, high income nations such as the United States had better air quality results.  The United States has a regulatory presence in the air pollution field with the Environmental Protection Agency, state agencies such as the State of Washington's Department of Ecology and local agencies such as the Puget Sound Clean Air Agency providing regulatory oversight. 

Air pollution is a global problem, as it can cross borders with global air flow.  The regulatory climate in one nation may impact other nations downwind from it. Thus nations are concerned about the regulatory climate in other countries.

The impact of air pollution goes beyond the health issues pointed out in the WHO article.  It also impacts economic relationships between countries.  Corporations arbitrage the cost in complying with air pollution regulations in their decisions as to where to locate by excluding the economic cost of externalities in pricing. 

Countries who do not have as stringent air pollution regulations will thus attract more business due to the lower costs associated with lesser compliance.  This results in consumers purchasing goods at lower prices, which do not reflect the externalities associated with the degradation in air quality. These externalities include the costs of increased morbidity and mortality of not only those in the area producing the pollution but in those areas downwind which may be subject to the pollution.  The downwind spread will reflect the nature of the pollutant and atmospheric conditions.

The above photo was taken in the Strait of Juan de Fuca between Washington State and British Columbia, looking west, through the haze, on a calm fall day.  The haze reflects the impact of suspended particulates, atmospheric aerosols, and the marine air mass.  Another photo, taken looking east on the same day, shows the impact of forest fires in Eastern Washington on air quality in views of Mt Baker and the Cascade Mountains.  

It is an interesting exercise to consider the relative contributions of air pollution from foreign and domestic sources.  This is especially challenging when atmospheric conditions encourage the mixing of different sources in a stagnant setting and contributions to health issues need to be considered.   An article in the Smithsonian (1/21/14) discusses contributions of air pollution from China to air pollution in the United States.