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Atmospheric Chemistry

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Atmospheric Chemistry

The three-legged stool depicting the interconnected nature of model, laboratory, and field studies within atmospheric chemistry and how it impacts society and environmental policy (from Burkholder et al. 2017)
The three-legged stool depicting the interconnected nature of model, laboratory, and field studies within atmospheric chemistry and how it impacts society and environmental policy (from Burkholder et al. 2017)

Atmospheric chemistry examines the composition of and chemical processes occurring within the Earth’s atmosphere as well as their perturbations by anthropogenic changes, and the resulting implications for weather, climate, and the biosphere. Research in atmospheric chemistry focuses in three primary areas: field observations, laboratory studies, and atmospheric modeling and they often support each other like the legs of a stool (see figure at left). 

For example, several field campaigns have demonstrated that the production of secondary organic aerosol (SOA) and small organic acids is more rapid then most box models can explain.  Therefore, many scientists have conducted laboratory and chamber studies to refine the understanding of the underpinning mechanisms driving the chemistry occurring on aerosols and in clouds. Under Dr. Pillar-Little’s leadership, CASS is using remotely piloted aircraft systems (RPAS) to collect trace gas, aerosol, and meteorological data in the atmospheric boundary layer (ABL) to explore a variety of topics at the intersection of weather, climate, and chemistry.

The center’s current ongoing projects are addressing the following broad themes: 1) identifying drivers influencing variations in the vertical structure of carbon dioxide (CO2), 2) determining the role aerosols play in convection initiation and intensification, and 3) examining the influence of meteorological conditions on local and regional air pollution, also known as chemical weather. 

Vertical Structure of CO2 in the ABL

Atmospheric scientists have been interested in studying fluctuations on atmospheric [CO2] because of its role in driving climate change as a greenhouse gas and as a central player in the global carbon cycle. Surface measurements of CO2 are recorded by a sparse network of tall towers, like the one at Mauna Loa, Hawai’i, which provides an excellent temporal record of the global rise of [CO2] over the last 40-50 years. But what’s going on aloft in the atmosphere?

It’s hard to say. Satellite data has limited temporal resolution and reports back on the total column concentration of CO2 and may miss fluctuations near the surface from emission sources such as fossil fuel combustion and vegetation. The biosphere breathes. CO2 is consumed via photosynthesis during the day and is expelled via respiration at night.  Vegetation also has seasonal variations too, with intense photosynthesis occurring during the spring green-up and over the summer, then tapering off through fall to a minimum in the winter. This diurnal and seasonal variability is often picked up by surface measurement stations, such as flux stations and tall towers, as well as some manned aircraft missions. 

Diurnal variation in carbon dioxide vertical profiles observed by manned aircraft (upper panels) and a tall tower (lower panels) on August 9 and 10, 2004. Black horizontal bars in the top panel represent the top of the ABL during each flight and open circles in the lower panels represent concentrations measured in the ABL by the aircraft (from Sasakawa et al 2013) Diurnal variation in carbon dioxide vertical profiles observed by manned aircraft (upper panels) and a tall tower (lower panels) on August 9 and 10, 2004. Black horizontal bars in the top panel represent the top of the ABL during each flight and open circles in the lower panels represent concentrations measured in the ABL by the aircraft (from Sasakawa et al 2013)

We hypothesize that the vertical gradient in the ABL is more significant than can be observed with surface based or manned aircraft alone and are developing a payload called the Lower Atmosphere CO2 Acquisition System (LACAS) that will allow us to take vertical profiles of CO2, temperature, and humidity using a CopterSonde or fixed-wing RPAS.

An area of particular interest for this work is to investigate how land-atmosphere coupling can influence short-term variations in diurnal and seasonal scale vertical variations in the CO2 vertical structure.  

Some specific current and future projects related to atmospheric chemistry include:

  • Investigating the feasibility of using remotely piloted aircraft systems (RPAS) to validate remote sensing methods (satellites, AERI, etc) for monitoring carbon flux and atmospheric [CO2]
  • Determining how aerosol loading can influence the timing and intensity of convective initiation
  • Examining how meteorological and chemical parameters impact aerosol formation and size distribution
  • Studying how chemical trends in the atmosphere on the sub-seasonal scale could be an early warning sign for flash drought
  • Developing an economical RPAS that can measure CO2, VOCs, O3, aerosols, pressure, temperature, and humidity in the boundary layer