Submitted to J. Aerosol Science
Paper presented at the Meeting "History of Aerosol Science"
Vienna, Austria, August 31-September 2, 1999
Atmospheric Aerosol Science Before 1900
Rudolf B. Husar
Center for Air Pollution Impact and Trend Analysis
Washington University, St. Louis, MO 63130
Abstract
The atmospheric aerosols have a rich history. Atmospheric aerosol science (i.e. the
explanations of the origin, pattern and properties) has emerged in the era of
Enlightenment (1700-1800) with the appearance of many new ideas, good and poor. The
origin of atmospheric aerosol was attributed to earthquakes, thunderstorm lightning,
meteoric dust as well as to volcanoes, windblown dust and combustion processes. By the
late 19th century, atmospheric observations and the use of simple physico-chemical
principles allowed the consolidation of the ‘theories’; earthquakes, lightning and
meteorites were eliminated as significant aerosol sources. In the 1800s, long-range
transport of aerosols was well understood. Particularly noteworthy are detailed
observations by Prestel on the regional peat smoke transported over north-central Europe
and the Krakatoa volcano study by Kiessling. As early as 1820, Rafinesque has
postulated that ‘dusty particles may be formed in the great chemical laboratory of our
atmosphere’. Systematic and quantitative measurements of atmospheric aerosol
properties have begun with Aitken in the 1880s. Already a century ago, scholars have
complained, “so impossible is to keep our heads above the rising tide of the new
meteorological literature that we are neglecting, to our loss, the rich stores which lie
buried in the books of a generation ago”.
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Introduction
The scientific questions regarding atmospheric aerosols have not changed much over the
past three centuries: Where do atmospheric aerosols come from? What are their physical,
chemical, and optical characteristics and their spatial-temporal pattern? What are their
effects? However, the answers given to these questions have varied considerably
throughout the past few centuries. The purpose of this paper is to illustrate to evolution of
atmospheric aerosol science prior to the 20th century. In the present context, ‘science’
refers to the explanations given to the above questions and the to the methods used to
derive these explanations.
The rapid growth in modern atmospheric aerosol science began in the 18th century, in the
era of Enlightenment in parallel with the rapid growth natural sciences in general. This
period was marked by the emergence of naturalists, architects, engineers, and
geographers. Many questions were raised and numerous new ideas were generated. The
main issue addressed by the pioneers of modern atmospheric aerosol science was the
origin of atmospheric aerosols. They have formulated theories regarding the aerosol
origin, some good, some less so. The scientific approach in this era consisted of
presenting theories without particular effort to back them up with appropriate evidence
either from observations or through consistency with the laws of nature. Consequently,
many of the early ideas on the sources, properties, and behavior of atmospheric aerosols
were without foundation and have not survived later scientific scrutiny. A brief review of
the key ‘theories’ is given in the next section.
During the 19th century, mainly the geologists studied atmospheric dust in connection
with soil formation (Udden, 1896). However, by the late 19th century meteorologists have
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also recognized the many influences that aerosols exert on the atmosphere: that the
presence of aerosols facilitates rain and snow formation; that aerosols influence both
visible and thermal radiation (Editor of Monthly Weather Review, 1901). Hence it was
recommended that the study of air composition should include gaseous substances as well
as atmospheric aerosols. About the same time, the role of atmospheric trace gases in
atmospheric radiative transfer was also recognized (Arhennius, 1896; Rodhe et al., 1998).
It could be said, therefore, that the late 19th century this was the beginning of modern
atmospheric chemistry, as a discipline separate from geology.
Atmospheric aerosol science during the 20th century addressed all the topics of previous
centuries. However, the methods of investigation have become increasingly quantitative
and explicitly included the use of laws of physics and chemistry, such as conservation of
mass and energy, as well as the laws of chemical kinetics. By the late 20th century,
computational models have also complemented conceptual models.
The resource materials for this historical review were collected by scanning the scientific
journals such as Monthly Weather Review, Meteorologische Zeitschrift, Philosophical
Magazine, and other journals. Meteorology textbooks from around 1900 were also
helpful. Doctoral dissertations, such as by Kempf (1914) on the theory of atmospheric
aerosols were particularly useful for tracing the pre-1900 literature as well as gaining
insights into the contemporary views. Unfortunately, many of the references cited by
Kempf (1914) could not be located for this review.
This is, of course, only an incomplete account of the history of atmospheric aerosol
science. A particularly severe limitation of this review is that it only considers western
literature from Europe and North America. Also, this historical review is focused on
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atmospheric aerosols on regional scale. Brimblecombe (1987) gives an in-depth account
of urban smoke pollution history in London.
Theories on the Origin of Atmospheric Aerosols
The most significant literature source for this historical review is a dissertation by
Nikolaus Kempf (1914) "Development of Theories on Regional Haze (Hoehenrauch) up
to 1870". Kempf defined regional haze as “strong atmospheric haziness (Truebung der
Luft) of relatively dry air with large spatial extent and longer duration”. This definition of
regional haze is consistent with the definitions used currently. Kempf has grouped the
existing theories on the origin of regional atmospheric aerosols into six categories: vapor
emissions from the Earth (earthquakes); electricity and thunderstorms; cosmic ash;
volcanic eruptions; windblown dust; combustion processes. Below is a brief summary of
these theories.
Haze form Gaseous Emissions from the Earth. According to this theory, atmospheric
haze can be attributed to bursts of gaseous emissions during earthquakes. For example,
Immanuel Kant (1756) in Locarno, Italy has observed that "in two hours a hot reddish
haze has spread over the valley and turned into red rain, which beyond doubt, is linked to
earthquake activity". It is likely that Kant has observed the intrusion and descent of a
Sahara dust cloud into the Locarno valley.
Marcorelle (1784) has noted that springtime warming causes the emission of
fermentation products to the atmosphere. He further suggested that sunshine evaporated
the water leaving only solid particles that constitute the springtime ‘dry fog’.
Conceivably, this theory represents the current category of biogenic emissions.
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Haze from Electricity.
Atmospheric haze from electrical discharges during
thunderstorms was a significant theory prior to 1850. According to Verdeil, (1783) "haze
is composed of droplets filled with electrical fluid that is attracted upward by the
electricity in the upper atmosphere" (thus prevents it from settling). Hoyer (1819)
proposed that "lightning dissociates water into H and O and the oxygen combines with
phosphorus to form phosphoric acid". He further argues that the smell of haze (ozone?)
clearly indicates its electrical origin. Schreiber (1844) also concludes that the peculiar
smell of the haze is due to the ozone produced by the electric discharges.
Evidently, the coincidence of ozone and electric discharge (lightning) as well as ozone
and haze has lead early researchers to the conclusion that lightning causes haze.
Haze from Meteoric Dust. Atmospheric haze from meteoric dust has also been
considered as a significant source of atmospheric aerosol. It was known that meteoric
dust burns up in the atmosphere and that the particles deposit onto the land. For example,
Benjamin Franklin (1784) has invoked meteoric dust as one of the possible theories to
explain the hazy and chilly year of 1783. Some early researchers argued that meteors
contribute "not less than 1 inch/century of solid material for the globe". Clearly, such
high accumulation rate is not supported by geological evidence. In fact, the overall
impact of meteoric or cosmic dust on the global budget of atmospheric aerosols is
thought to be insignificant (Junge, 1963)
Haze from Volcanic Emissions. Since ancient times it was recognized (e.g. Seneca, ca.
60 AD) that volcanic gases and ash cause local atmospheric turbidity. However, only in
the 1700s was discovered that volcanic aerosols are transported over large distances.
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Benjamin Franklin (1784) has noted that the “the year without summer” in 1783 may
have been due to the eruption of a volcano on Iceland.
Haze from Windblown Dust. Throughout history it was known that windblown dust
causes regional haze. Atmospheric dust and the associated atmospheric turbidity is a
common meteorological phenomenon that has acquired different names in various parts
of the world: harmattan (W. Africa), sciroco or calina (Spain). gobar ( E. Africa), haboob
(Arabia), kosa (Japan), whangsa (Korea), huangsha (China).
Haze due to Combustion Processes. Some atmospheric turbidity is caused by the solid
and liquid combustion products. In particular, smoke from forest and grassland fires has
been a known source of atmospheric haze over many parts of the world. The particular
role of anthropogenic fuel combustion during early industrialization in London is
reviewed by Brimblecombe (1987).
The scientific methods for establishing the causes and origins of the atmospheric aerosol
were outlined most clearly by Egen (1835). He points out that evidence for the causality
can be gained from: (1) direct observation, e.g. a visible smoke plume; (2) smell of the
air, which roughly corresponds to measuring the chemical composition of the aerosol; (3)
temporal variation; (4) decay with distance, i.e. the highest concentration is at the source;
(5) concentration change with wind direction, which corresponds to the current concept
of the pollution rose; (6) airmass trajectory analysis. Egen’s list of gathering evidence on
sources and for establishing source receptor relationship is virtually identical to the ones
used in current science on source-receptor relationship.
In summary, the 18th century was the beginning of modern scientific thinking on
atmospheric aerosols. The 19th century was the era of transition from theory-driven to
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observation-based atmospheric aerosol science. Theories were compared and
qualitatively reconciled with systematic observations. By the late 19th century, the
atmospheric observations along with the application of simple physico-chemical
principles allowed the consolidation of the ‘theories’ regarding the origin of atmospheric
aerosols. In particular, earthquakes, lightning and meteorites were eliminated as
significant contributors to regional aerosols.
Transport, Spatial-Temporal Distribution and Properties of
Atmospheric Aerosols
A scientific debate about the local versus long range transport of atmospheric aerosols
has continued throughout history. The discussion pertaining local versus long range
impact was particularly intense regarding impacts of smoke aerosols. According to
Kempf (1914), Sir Francis Bacon (ca 1600) has reported the first international long range
transport incident: the Gasgogners in southern France have complained to the King of
England that smoke from the springtime burning of seaweed in Sussex, England has
spoiled the wine flowers and ruined their wine crop.
In an extensive study, Wargentin (1767) and Gadolin (1767) have reported that forest
fires in Russia and Finland cause regional haze in Central Europe. They have also pointed
out that given the location of the fires, as well as the appearance of smoke at different
locations, the path of the smoke could be geographically mapped. Hence, Wargentin and
Gadolin may have been the first to conduct a systematic long-range transport study using
smoke observations and winds.
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The occurrence of regional haze in 19th century Northern Europe has a particularly
revealing history. Since the late 1700s Northern Europe was frequently under thick layers
of haze. The regional haze has covered much of the flatland north of the Alps extending
from Paris to Warsaw. Throughout the century, a scientific debate was in progress
regarding the causes, transport and effects of the thick haze. Again, drawing upon the
review by Kempf (1914), the cause of the regional haze was identified as agricultural
peat burning that begun in the late 1700s and peaked in 1850s. Throughout northern
Germany and Holland swamps were drained and the remaining dry peat deposits were
burned to obtain new farmland from the wetlands. The result was thick smoke from peat
fires that was lingering over the region, causing highly objectionable thick haze. Due to
public pressure and diminishing wetlands, the burning practice stopped by the 1870s.
Thus, the regional haze problem in Northern Europe has simply disappeared by the end
of the 19th century.
The methods of peat smoke investigation included studies on the sources, transport and
removal of the smoke particles. Some of the studies have even included the effects of
smoke on human health. A particularly clear illustration of the contemporary scientific
methods was reported in a series of articles by Prestel (1861). He studied the spatial and
temporal pattern and the long-range transport of smoke. He collected visibility
observations along with wind direction and wind speed from dozen of Cities along the
path of the smoke plume. He then mapped the advance of smoke plumes from their origin
in northwestern Germany and Holland toward the east and south (Figure 1). His data and
the associated analysis clearly documented both the origins of the smoke, as well as its
transport more than 1,000 km from the source. It is quite humbling that the use of surface
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visibility data to track the transport of smoke was re-discovered at least twice since
Prestel (1861). Wexler (1950) used it to track the dispersion of forest fire smoke and
Husar et al., (1980)tracked the transport of regional haze.
According to Danckelman (1884), regional haze from savannah fires in Africa has been
known since the Roman times. Danckelman himself has estimated the mass of globally
burnt grassland to be about 600 million tons and he compared that the global coal
consumption of 300 million tons. He then states that the entire smoke emissions from
steam engines and peat smoke in Europe is insignificant compared to the smoke produced
by these fires. This latter observation is particularly intriguing since the dominant role of
biomass burning on the global aerosol pattern is just being re-discovered.
The long-range transport of windblown dust has also been recognized for centuries. Dust
transport from the Sahara and Gobi deserts are well documented throughout the reported
history. For example, sailors traveling through the tropical Atlantic have frequently
reported dust depositing on their ships thousand of kilometers from the African continent.
Similarly, early geologists have recognized that loess deposits in many parts of the world
are due to atmospheric dust transported over long distances.
A significant early study of the spatial-temporal pattern of Sahara dust was reported by
Dinklage (1891). He analyzed the ship logs compiled by the English Meteorological
Office and by the German Seewarte in Hamburg. Based on 13 years of data, he found that
January and February have the most frequent dust events. He observed that the spatial
pattern of Sahara dust is a tongue-shaped extrusion from West Africa, extending at least
1400 miles from the coast. According to Dinklage, there was no doubt about that source
region of the dust: the African Deserts.
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Studying the dispersion of volcanic aerosols has an interesting history. Seneca, ca 60 AD,
states that volcano causes "gloomy cold and stains darkly the atmosphere of our region".
However, according to Kempf (1914) only in the 1700s was recognized that volcanic
aerosols are transported over long distances.
In 1883 red sunsets were observed throughout the world. Lacking a plausible explanation
for the ubiquitous atmospheric phenomenon, the British Royal Society has issued a
scientific competition to explain this unusual global phenomenon. The scientific price
was won by Kiessling (1888), who provided extensive and compelling evidence that the
red sunsets were due to the stratospheric aerosol of the Krakatoa volcano which erupted
in 1883. The Kiessling (1888) study was also a major contribution to dynamic
meteorology, since it revealed, for the first time, the existence of a general global
circulation of the atmosphere. Furthermore, the Krakatoa volcanic aerosol along with
Kiessling's explanations have demonstrated that atmospheric aerosols are unique
visualizers of atmospheric transport processes.
To our knowledge, the first aerosol chemical mass balance data were collected by M.
Barac in Fiume, (now Rijeka, Croatia), and summarized by the Editor of Monthly
Weather Review (1901). He analyzed the chemical composition of dust particles during a
Sahara dust event over the Adriatic Sea. The resulting chemical composition pie chart is
given in Figure 2. Using light microscopy, he also observed that the dust is of bright
reddish color. Under polarizing light, most particles were colorless, irregular fragments of
crystals together with skeletons of microorganisms and small particles of soot. The dust
fallout averaged between 260 and 1400 g/m2 in Fiume (a questionable high deposition
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rate). According to the Editor of Monthly Weather Review (1901) the Fiume dust belongs
to the same class as the trade wind dust which blows from Africa over the Atlantic.
In discussing the Barac data, the Editor of the Monthly Weather Review (1901) added
that the "effect of this dust floating in the atmosphere was to produce a reddish haze and
to diminish the amount of insolation at the earth ’s surface thereby doubtless increasing
the temperature of the air in the upper strata". The radiative heating and cooling effects of
haze, dust, smoke aerosols is still an active research area.
Formation and Removal Processes
In the 17th century, many scientists have invoked rather mysterious processes for the
formation of atmospheric aerosols, including electrical discharge, earthquakes, and
meteorites. We will refrain here from belaboring these unsubstantiated theories. Most of
the scientific explanations on the formation and removal of atmospheric aerosols were
consolidated during the 19th century.
It is fascinating that among the myriad variety of theories, some remarkably clear and
complete explanations on atmospheric aerosols were also available already 200 years
ago. For the contemporary scientists, the key problem was of sorting out the good
theories from the bad ones. A most remarkable sets of explanations on the formation and
behavior of atmospheric aerosols were provided in several articles by Rafinesque (1819),
based on his vast experience in earth and biological sciences. Rafinesque summarized his
understanding in an essay "Thoughts on Atmospheric Dust". Rafinesque states that "Dust
exists even on the tops of the highest mountains". Thus, he recognized that aerosol
particles are mixed throughout the lower layer of the atmosphere. "It settles slowly in
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clear weather but is quickly washed down by rain and snow". Clearly, he understood the
roles of dry and wet removal processes. "Some dust is from the pulverization of road and
field surfaces." Recently, Rafinesque’s contribution to American science were recognized
in an article in the Smithsonian Magazine (1995).
The most insightful contribution of Rafinesque pertains to secondary aerosol formation:
"A portion (of the dust) is formed chemically in the atmosphere by combination of gases
and elementary particles dissolved in the air".
A published dialog of Rafinesque (1820) with an anonymous reader further clarifies his
position. According to an anonymous reader: "All dust comes from the action of the
wind, even the dust at sea, carried 1500 miles over the Atlantic". Rafinesque's response:
"I do not deny that the winds raise terrestrial dust and often carry it to distance; but I
assert ...with Virey, Patrin, Deluc, and other philosophers, that there must be another
independent formation of dust in the besides the scanty terrestrial supply wafted by the
winds". Evidently, there were other thinkers before Rafinesque, who recognized the role
of secondary aerosol formation. "We know that sulfur, muriate of ammonia, etc. can be
formed by sublimation of gases". "That smoke soot, volcanic productions, meteorites,
earths, and even stones or metals may be spontaneously combined by a casual meeting of
gaseous emanations." "It is not, therefore, difficult to conceive how dusty particles may
be formed in the great chemical laboratory of our atmosphere."
It is quite revealing the manner in which Rafinesque has concluded that secondary
aerosol formation must be a significant mechanism for the formation of atmospheric
haze. He simply observed the rays of sun and deduced: "the sun rays are not an optical
reflection from the atmosphere since it is brighter and not so azure. It must be dust. The
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phenomenon can be seen even after long and heavy rains that precipitated all the
terrestrial dust to the ground. Whence the dust must be continually formed in the
atmosphere."
Experimental verification of Rafinesque’s theories on secondary atmospheric aerosol
formation occurred only eighty years later. In a long and careful series of studies, John
Aitken (1884, 1885, 1888, 1891) has observed that on cloudy days the nuclei count
remained low. The nuclei number concentration has increased in proportion to the
sunshine.
Aitken noted that “sunshine may produce some change in the
(photochemically active) constituents of the atmosphere which gives rise to nuclei
formation in saturated air”. He also observed that the high nuclei days were not hazy
which suggested to him that the nuclei were of “molecular dimensions”, below the
visibile size range.
Evidently, John Aitken (1985) was also the first to use the concept of chemical mass
budget to support his reasoning. He states that densely inhabited areas ‘lose their purity’,
in other words they accumulate particulate matter. “Purifying areas of the world are those
regions that lose more impurity than they gain”. Without knowing of Rafinesque’s
theories, Aitken states that “the deposition of vapor on these particles seems to be the
method adopted by nature for cleansing them away. Hence cloudy and rainy regions (of
the world) are the most purifying.” It is ironic, that at the dawn of the 21st century we
still do not have a clear understanding of which are the cleansing and which are the
aerosol accumulating regions of the world.
John Aitken has also developed an elegant and still valid method of analyzing the
relationship between the particle concentration and visibility. He proposed that visibility
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should be defined as the limit at which objects are visible; observations on rainy days
should be discarded and the data were to be classified according to humidity. From his
long-term observations Aitken found that the amount of haze was proportional to the
number of particles and that the product of nuclei concentration x visual range was a
constant. This corresponds to the modern observations that the horizontal aerosol
extinction coefficient is generally proportional to fine particle mass concentration. Finally
Aitken found that the aerosol extinction in moist air is twice the value in dry air.
Other researchers have concluded that the beautiful sky colors produced by volcanic
aerosol from Krakatoa and Pelee must have been produced by droplets of condensation. It
was argued, that it would require a long mechanical grinding to make such a uniformly
fine impalpable powder.
Discussion
The summary and conclusion of this review I given in the Abstract of this paper. Below
are several additional observations. Comparing the scientific language before 1900 and
after 1950 one can notice that the words 'doubtless', 'beyond doubt', 'clearly' have
virtually disappeared from the scientific vocabulary. One wonders, why? The review of
the historical literature also reveals several universal truths regarding the lack of recycling of already crafted knowledge. Kempf (1914) for instance observes, “early
researchers on regional haze paid little attention to the past theories - possibly due to the
fact that they were not as easily accessible as today”. The situation in year 2000 does not
appear better; it may be worse. In another universal observation, Ward (1914) notes: “So
impossible is to keep our heads above the rising tide of the new meteorological literature
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that we are neglecting, to our loss, the rich stores which lie buried in the books of a
generation ago.”
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Figure 1. The spatial and temporal pattern and long-range transported smoke,
based on visibility observations at dozen of sites (Prestel, 1861).
Figure 2. Aerosol chemical mass balance of dust collected in Fiume by Barac,
reported by Editor of Monthly Weather Review (1901).
19
20
Chemical Mass
Sahara DustBalace
at Fiume, March 10-13 1901
M. Barac
Si O2
Al2 O3
Ca O
Fe2 O3
C O2
Mn3 O4
Mg O
Organics
Traces
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