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Measurements of Aerosol Vertical Distribution

By Andrea Baccarini, University of Trento, Italy

My name is Andrea, I’m a master’s student in physics from the University of Trento and I spent a couple of months in the Azores for my master’s thesis.

I’m studying the aerosol vertical structure from Pico, a remote island of the Azores, with a stratovolcano. An atmospheric observatory with meteorological observations is located at the top of the volcano. The position of that station is very particular, in fact thanks to its elevation it is situated in the so called “free troposphere”. And, for which reason should this matter? It matters, because it allows us to study air that comes from far away places, typically the North America. Within a certain approximation, we can say that the free tropospheric air is not influenced by the local emissions (I mean the emissions from the island itself) . This is motivated by the fact that the beginning of the free troposphere (called the boundary layer) is characterized by a thermal inversion (Figure 1). Thanks to the thermal inversion, the air masses do not easily exchange components at the boundary layer. The identification of the boundary layer is pretty easy if there are low clouds. In fact in that case the height at which the clouds disappear corresponds to the beginning of the free troposphere.


Figure1: The caldera of the Pico volcano with a visible thermal inversion as seen by the confined clouds.

However every time we speak of the atmosphere, we must keep in mind that the situation could be really dynamic, especially if you are on a remote island in the middle of nowhere, exposed to every kind of perturbation. For this reason, it is important to characterize the vertical structure of the atmosphere and to understand within which conditions measurements done at the observatory can be considered to be independent from local emissions.

How do I do this vertical characterization? 

In theory it is pretty simple; I put all my instruments in a backpack and hike (Figure 2), starting from an elevation of about 1200 meters above sea level to the Pico Mountain Observatory (2200 meters above sea level). In my backpack, I have an instrument that collects pressure, temperature and humidity,  although it is pretty small I usually put this instrument into a big case to protect it from direct exposure to solar radiation. I also have a nephelometer, this is the biggest instrument, and it measures the light scattered from the particles present in the atmosphere (i.e. Aerosol, dust, etc…). Moreover I carry a particle counter which allows me to measure the concentration of particles with diameters above 0.3 μm and 0.5 μm. This instrument is especially useful because it allows me to distinguish between the dust particles, generally bigger than 0.5 μm, and the combustion aerosols that are generally smaller. Finally I have a sunphotometer, an instrument that measures the intensity of the sunlight that reaches the detector. In this way, it is possible to have an idea of the quantity of haze present into the atmosphere above the observer. In addition to all these instruments, I also use a GPS in order to track my position and my elevation.


Figure 2: Andrea Baccani with his measurement backpack

A Strange Event

Recently, we noticed a very interesting event that I will describe briefly without much technical detail. On a clear day, with clouds well below the top of the mountain we noticed something unusual. Thin grey layers above the clouds are often visible and are an indication of the presence of some kind of particulate, like aerosol from anthropogenic emission or biomass burning, dust, etc… However on this specific day we noticed a particularity: the layer above the clouds was composed of three well-defined sub layers (Figure 3). This was the first time we observed an event like that and it would be very interesting to understand why that triple stratification happened and if the composition of the layers was different or not.


Figure 3: A photo of the aerosol layers above the clouds. High contrast was used to clarify the image (blue box).

The most interesting part is that these three layers were also present in my profiles measurement and this provides us with good informations about the height and the thickness of the layers.

To show this to you, I will use a couple of graphs. The first graph is the particle concentration profile (Figure 4). On the vertical axis there is the elevation while on the horizontal axis there are the particle concentrations. The particles with a size above 0.3 micron are shown in green and those above 0.5 micron are shown in blue. The first thing to notice is that both of the signals have a clear decrease around 1500 meters. This is likely associated with the passage into the free troposphere and is supported by the temperature profile that indicates an inversion at the same height (not reported here). Above the boundary layer there are evident variations in the signal of small particles concentration,while the signal for the bigger particles seems to be pretty stable (around 0.3 particles for cubic centimeter). Because most dust particles are bigger than 0.5 microns we may exclude the presence of dust in the layers. This is pretty important because dust is generally the most abundant type of remote atmospheric aerosols.


Figure 4: The particle concentration profile observed from the Pico Mountain profile measurements. 

Now we can notice that at the moment of the measurements, the first layer was approximately 450 meters thick, starting at a height of 1600 meters and ending at 2050. The second starts around 2100 meters and ends at 2250 meters and for the third later we can observed only the beginning at approximately 2300 meters above the sea level. Clearly the identification of the position of the layers is subjected to some uncertainties that we estimate to be approximately around 50 meters.

In order to confirm these observations we will look at the nephelometer data shown in the graphs below (Figure 5). The elevation is again on the vertical axis and the scattering coefficient is on the horizontal axis. The scattering coefficient, is a measure of the light scattered intensity (it corresponds to the size and the number of particles that scatter the light). In this data the three layers are somewhat less evident because the level of noise is higher, however their position corresponds quite well to those measured with the particle counter.


Figure 5: The aerosol scattering  profile observed from the Pico Mountain profile measurements. 

In summary, we measured the three aerosol layers above clouds with two different instruments. These measurements provide evidence to conclude that what we measured is effectively what we saw looking at the horizon and was not an artifact. However at this moment, this is only a preliminary analysis that requires further technical investigations in order to be confirmed. Moreover, it will be interesting to analyze additional data collected at the station in order to obtain more information about these layers and maybe understand their composition and origin. So, stay tuned because maybe some updates will come!!!

See also – Portuguese News about this study

Paulo Fialho

imagePaulo Fialho, Ph. D.

Professor of Chemistry at Azores University

Research Gate Profile


Dr. Fialho is a founding collaborator of the Pico Mountain Observatory.  He has been measuring black carbon at the site since 2001.

Dr. Fialho is the primary point of contact for activities at the Pico Mountain Observatory.

Claudio Mazzoleni

IMG_4386Claudio Mazzoleni, Ph. D.

Associate Professor of Physics at Michigan Tech

Research Group Webpage

Google Scholar Profile

Dr. Mazzoleni is the principal investigator of the Department of Energy funded research at the Pico Mountain Observatory to study the optical properties of aerosol above marine clouds.  His group’s most recent technical publications from this work include: “Morphology and mixing state of aged soot particles at a remote marine free troposphere site: Implications for optical properties” and “Perturbations of the optical properties of mineral dust particles by mixing with black carbon: a numerical simulation study“.

Lynn Mazzoleni

IMG_5515 Lynn Mazzoleni, Ph. D.

Associate Professor of Chemistry at Michigan Tech

Research Group Webpage

Google Scholar Profile

LinkedIn Profile

Dr. Mazzoleni is the principal investigator of the National Science Foundation funded work at the Pico Mountain Observatory to study long-range transported aerosol.  Her group’s most recent technical publication from this work is titled, Molecular Characterization of Free Tropospheric Aerosol Collected at the Pico Mountain Observatory: A Case Study with a Long Range Transported Biomass Burning Plume. (Read more)

Detlev Helmig

 dhelmigDetlev Helmig, Ph. D.

Associate Research Professor at the  Institute of Arctic and Alpine Research (INSTAAR)

Research Group Webpage

Pico Mountain Research Webpage


Dr. Helmig has been working at the Pico Mountain Observatory since 2004.  His expertise involves measuring trace gases at very low concentrations in remote environments.  His group’s most recent publication from research at the Pico Mountain Observatory is titled, “Climatology and Atmospheric Chemistry of Non-Methane Hydrocarbons Ethane and Propane over the North Atlantic” to be published in Elementa.

Research Personnel and Collaborators

Postdoctoral Researchers

Katja Dzepina, Postdoctoral Researcher in Chemistry at Michigan Tech, 2012- 2014

Dr. Dzepina worked at the Observatory in 2012 and 2013. She is the lead-author of “Molecular Characterization of Free Tropospheric Aerosol Collected at the Pico Mountain Observatory: A Case Study with a Long Range Transported Biomass Burning Plume” a technical paper published in Atmospheric Chemistry and Physics, 2015 (Learn more).

She is currently at the University of Rijeka (Curriculum Vitae).

Sumit Kumar, Postdoctoral Researcher in Physics at Michigan Tech 2012 – 2013

Dr. Kumar worked at the Observatory in 2012. He is finalizing a technical paper in collaboration with Dr. Paulo Fialho about the observed trends in black carbon over the years 2001 – 2014. He has also presented his work at the American Geophysical Union Fall Meeting in 2012.

He is currently at the National Center for Medium Range Weather Forecasting, Noida, India (Contact information).

Graduate Student Researchers

Kendra Wright, Ph. D. Student in Physics at Michigan Tech, 2012 – Current 

Kendra Wright was awarded a NASA graduate fellowship for her doctoral research related to novel measurements of black carbon to be done at the Pico Mountain Observatory.  She has worked at the Observatory in 2013 and 2014 and she is currently working with data collected over 2012-2014.  She presented some of the preliminary results of her research at the American Geophysical Union Fall Meeting in 2013 and 2014.

Simeon Schum, Ph. D. Student in Chemistry at Michigan Tech, 2013 – Current

Simeon Schum is working on the molecular characterization of aerosol samples collected at the Observatory.  He participated in fieldwork in 2014 and he is the lead chemist for the measurements of water-soluble ions.  He is also working on a new technical publication regarding the detailed composition of long-range transported biomass combustion plumes.

Bo Zhang, Ph. D. in Environmental Engineering, Michigan Tech, 2009 – 2015

Dr. Zhang worked with samples and data collected at the Pico Mountain Observatory.   He is the lead-author of a technical paper titled, “A Semi-Lagrangian View of Ozone Production Tendency in North American Outflow in the Summers of 2009 and 2010” published in Atmospheric Chemistry and Physics, 2014 (Learn more).  Currently, he is finalizing a publication about the age of long-range transported aerosol collected in 2013 using radioactive isotopic measurements.  Dr. Zhang also conducted FLEXPART trajectory analyses for a climatological analysis of the site over several years.

Bo is currently working as a postdoctoral researcher at the National Institute of Aerospace (Brief biography).

Lorentyna Harkness, M.S. in Applied Science Education, Michigan Tech, 2014

Lorentyna Harkness is a professional K-12 science teacher. She participated in fieldwork at the Pico Mountain Observatory in 2013 and developed a novel set of multimedia teaching materials for teachers of middle school science students.  The curriculum focuses on the science of the Pico Mountain Observatory research projects and the scientific process (Click here).

Swarup China, Ph. D. in Atmospheric Science, Michigan Tech, 2009 – 2015

Dr. China worked with our group on samples collected at the Observatory in 2012, 2013 and 2014.  He is the lead-author of a technical paper titled, “Morphology and Mixing State of Aged Soot Particles at a Remote Marine Free Troposphere Site: Implications for Optical Properties” published in Geophysical Research Letters, 2015 (Learn more). He is also a co-author of another technical paper titled,  “Perturbations of the Optical Properties of Mineral Dust Particles ” published in Atmospheric Chemistry and Physics, 2015 (Learn more).

Swarup is currently working as a postdoctoral researcher at the Pacific Northwest National Laboratory (Brief biography).

Andrea Baccarini, M.S. Student in Physics at the University of Trento, Italy

Andrea Baccarini is working at the Pico Mountain Observatory this summer (2015).  He is a masters student in Physics at the University of Trento, Italy.  He is collecting measurements to study the stratification of the atmosphere using backpack instrumentation while hiking from the Casa da Montanha (1225 m asl) to the top of the Pico volcano (2351 m asl) for his thesis research. Currently, he measures relative humidity, temperature, pressure, particle concentration, particle scattering and solar irradiance when the weather permits.


Noel Urban, Professor of Environmental Engineering at Michigan Tech (Professional page)

Judith Perlinger, Professor of Environmental Engineering at Michigan Tech (Professional page)

Robert Chris Owen, Scientist at the U.S. Environmental Protection Agency; Adjunct Professor of Geology at Michigan Tech (Linked IN profile)

Donald Wuebbles, Professor of Atmospheric Science at the University of Illinois (Professional page)

Sarah Green, Professor of Chemistry at Michigan Tech (Professional page)