Molecular and Physical Characteristics of Aerosol at Pico Mountain Observatory in the Azores

Mazzoleni, L. R., Michigan Technological University

Aerosol Processes

Aerosol Processes

Schum S, B Zhang, K D┼żepina, P Fialho, C Mazzoleni, and L Mazzoleni. 2018. "Molecular and physical characteristics of aerosol at a remote free troposphere site: implications for atmospheric aging." Atmospheric Chemistry and Physics, 18(19), 10.5194/acp-18-14017-2018.


The Pico Mountain Observatory (2225 m asl) is located in the summit caldera of the Pico Volcano in the Azores (summer 2015)



A brown aerosol layer above the marine clouds photographed while descending from Pico Mountain.



The Pico Mountain Observatory (2225 m asl) is located in the summit caldera of the Pico Volcano in the Azores (summer 2015)


A brown aerosol layer above the marine clouds photographed while descending from Pico Mountain.

Science

Oxidation plays an important role in governing the interactions of organic aerosol with clouds and atmospheric heterogeneous chemical reactions. To learn more about the chemistry of long-range-transported free tropospheric aerosol, we studied the molecular composition of organic aerosol collected at the Pico Mountain Observatory in the Azores. 

Impact

We observed aerosol transported in the free troposphere to be less oxidized than aerosol transported in the boundary layer. This has implications for the lifetime of aerosol transported in the free troposphere, where the relative humidity and temperature are lower compared to the marine boundary layer.  This is especially relevant for pyro-convected wildfire emissions, including brown carbon, and therefore may be important for an improved understanding of the role of aerosol on Earth's radiative balance.

Summary

Three aerosol samples collected at the Pico Mountain Observatory in the Azores were analyzed using ultra-high-resolution mass spectrometry to determine their molecular compositions. Two samples exhibiting an overall lower extent of oxidation were transported in the free troposphere and had been aloft for approximately one week, as demonstrated by back trajectory simulations using FLEXPART. The ambient relative humidity and temperature were retrieved from the Global Forecast System data for the air masses corresponding to the FLEXPART retroplumes and were used to estimate the RH-dependent glass transition temperatures of the identified components (DeRieux et al., Atmospheric Chemistry and Physics, 2018). The RH-dependent glass transition temperatures for the less-oxidized samples indicated a relatively higher organic aerosol viscosity, implying a decreased susceptibility to oxidative processes. One sample, in particular, was heavily influenced by wildfire emissions and showed evidence of brown carbon after long-range transport. Previously, a majority of the brown carbon associated with wildfire emissions was expected to have a lifetime on the order of one day. In contrast, a sample with anthropogenic influence and transported in the boundary layer was much more oxidized despite a shorter transport time (~three days). These findings indicate the importance of the transport path and ambient conditions on the lifetime of organic aerosol.