ITES PROFESSOR

Olga Mayol-Bracero

The Institute for Tropical Ecosystem Studies (ITES) has investigated the earth, flora, fauna, streams, rivers, lakes, estuaries, weather and rainfall patterns, natural disturbances, and land-use changes in Puerto Rico for fifty years. With the addition of Atmospheric Chemist Olga L. Mayol-Bracero, Ph.D. to their faculty in 2002, ITES also concentrates on air, specifically atmospheric aerosols and clouds in the tropics. “Aerosols are liquids or solid particles suspended in a gas. When you talk about atmospheric aerosols, this gas is going to be air,” explains Mayol-Bracero.

“We breathe them in. They come from different sources. Depending on their chemical composition and size, some can be very harmful to humans or plants, or they can degrade exposed structures through chemical reactions. Aerosols can also have an impact on climate and visibility,” says Mayol-Bracero. Hazy days in Puerto Rico, for example, may be caused by African (Saharan) dust that blows across the Atlantic and affects air quality. This dust also affects visibility, mostly during the summer months because the aerosol particles interact with light. “The desertification of Africa from overgrazing is contributing to creating more of the dust that’s carried in the winds. Climate change is definitely aggravating desertification.”

Mayol-Bracero’s postdoctoral work with the Max Planck Institute brought her to the Maldives, an island nation consisting of a group of 26 atolls in the Indian Ocean, about 435 miles southwest of Sri Lanka. She and other scientists, as part of the INDOEX project, studied the aerosols generated in Southeast Asia, India, and China and brought by wind to this small nation. They found an enormous amount of air pollution in the Republic of Maldives, which has little industrial pollution of its own. “During the dry season, the brown haze layers can reduce the solar heating of the ocean, reducing evaporation of water and thereby decreasing tropical rainfall and perturbing the water budget. They can also reduce sunlight, which could have an effect on terrestrial and marine biological productivity. We measured the aerosols and trace gases from the C130 Hercules airplane of the National Center for Atmospheric Research. Several publications on this work presented results so shocking to the scientific community that several additional field campaigns were performed in this region and a permanent sampling station/laboratory has been established.”

Although Puerto Rico receives wind-borne pollution from North Americas well as Saharan dust, the effects are not as harmful as they could be. “We’re lucky in Puerto Rico because the geographic and meteorological conditions favor the dispersion of our own pollution and that generated elsewhere. When we get the trade winds, and in the absence of African dust, we have clean air mostly with marine particles, free of anthropogenic pollution.”

Mayol-Bracero’s work involves intense periods of air sampling and much time devoted to analyzing the aerosols’ chemical and physical properties. Aerosol particles can have an impact on climate because they scatter or absorb solar radiation in the atmosphere and affect cloud condensation nuclei concentrations, thus cloud albedo, or reflective power. To understand these effects, information on the size and chemical composition of the particles is essential.

There are several ways to sample air. Some instruments pull air through one or more filters and then the filters are analyzed in the laboratory to determine their chemical components. “We also use online instruments that provide real-time measurements of aerosol properties. Some measure how the particle interacts with radiation—how much light these particles scatter and/or absorb. We also study size–resolved chemical composition. Size is important because it gives you an idea of the source of the particles. For example, very small particles usually come from anthropogenic pollution, and the larger ones are usually of biogenic nature.” The smaller the particles, less than one micron, the more dangerous they are for humans because they can permeate our mucus membranes and enter our respiratory systems.

Aerosols also play a role in heating or cooling the atmosphere. “In general terms, if nothing else is happening and you have a particle that tends to scatter radiation effectively, the net result will be a cooling of the surface, and vice versa for particles that absorb. Particles are better known for scattering.

“There are just a few chemical species that can actually be related to absorption. One of these is black carbon; another is the oxides of iron. In the atmosphere there is a mixture of different aerosols. In order to determine the state of cooling or warming, we need to use climate models that take into account the radiative properties of the particles. Some can also take into account the aerosol chemical composition.”

An important result from Mayol-Bracero’s aerosol analyses is the impact of anthropogenic pollution from North America on the chemical and physical properties of aerosols in Puerto Rico. This has been part of the research project of doctoral student Flavia Morales. For example, in samples of air masses coming from North America, Morales observed much higher sulfate concentrations than in clean air masses from marine origin. “When chlorine is decreasing, as in an anthropogenic case, you have what is called sea spray acidification, which means that acids, such as nitric or sulfuric, in polluted air masses that come, in this case, from North America to this region, are depleting the chlorine in these particles,” says Mayol-Bracero. “They’re taking up chlorine from sodium chloride and this chlorine is volatilized as HCl. Even though the concentrations of the species that are characteristic of pollution are low, you can see the effects of anthropogenic emissions in the aerosol chemical composition.”

Mayol-Bracero is also investigating the spatial and temporal variability of aerosol chemical and physical properties and how these aerosols impact the microphysics of trade wind cumuli. The NSF funded projects Rain in Cumulus over the Ocean (RICO) and its Research Experience for Undergraduates (REU-RICO) gave her the opportunity to work with students in field projects in Puerto Rico, Antigua, and Barbuda to study these aspects of aerosols and clouds. “We also looked at cloud chemical and physical properties. We were trying to determine how much time particles spend in the air. We wanted to see what species in the aerosol phase are more efficiently removed by clouds and how this depends on the particle’s chemistry and size. The rate of removal of different species impacts their atmospheric residence time and thus their influence on indirect and direct aerosol climate forcing.” This part of the research is performed by postdoctoral Adriana Gioda, as part of Mayol-Bracero’s group.

Currently, several of Mayol-Bracero’s students are chemically and physically characterizing African dust. These dust particles seem to produce an effect in precipitation similar to urban or biomass burning particles. “If many small particles are introduced into a cloud, the water will need to be shared with the new particles; therefore, the cloud droplets will become smaller, sometimes so small that they will not be able to precipitate. They stay longer as clouds and do not drop the rain. There are a several papers on effects of aerosols coming from biomass burning and from urban pollution on precipitation, but I haven’t seen many clearly saying that African dust has the same effect. This is definitely an interesting area of research for the Caribbean region.”

Other research Mayol-Bracero works on include field camps to chemically and physically characterize aerosols from the Fajardo Lighthouse (marine aerosols), Río Piedras campus (urban aerosols), East Peak (forest aerosols), and El Verde Field Station (forest aerosols); a collaborative project with the Max Planck Institute for Chemistry in Germany and the Lawrence Berkeley National Laboratory in which biomass burning aerosols (with particular interest in their carbonaceous fraction) in the Amazon basin are under study; and a project with students and scientists at Arecibo Observatory studying the optical properties of aerosols with remote sensing techniques. In addition she is working on a joint NOAA-CREST project with professors from UPR, Mayagüez involving ground-based sampling and remote sensing of tropospheric aerosols and comparison of the physical, optical, and chemical properties of these aerosols. Mayol-Bracero’s participation in this project has already produced interesting results with respect to the impact of African dust and ashes from the Soufriere Hills volcano on the properties under study.

omayol@adam.uprr.pr

Sudents Pamela M Vallejo, Lydia Liz Soto-García, Flavia Morales-García, Milton Repollet Pedrosa, and Gabriel Reyes with Professor Olga Mayol at Fajardo light house, where an aerosol sampling station is located. Absent from the research group: Cecille Villanueva, Gilmarie Santos, Adriana Gioda, Hector Rivera, Kristal Ibarra and Lourdes Santiago.

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