Summary for the first 2 weeks of research experience

Welcome to the research! In this first 2 weeks, I mainly focused on investigating the AMS data set we collected during the last semester. The ambient aerosol samples examined were collected in Toronto and Lethbridge, Canada (named CADO and CALE, with a total of 51 sample sets), and were run in the AMS of NASA. As a preliminary data processing step, I paid more attention on qualitative information: 1) the amount of organic matter in each sample run, 2) the organic composition of the collected aerosol sample, 3) the degree of oxidation of organics in each sample.

 

Let me show some examples for the results of this step of data analysis. The first picture shows a time series of an overall sample run during a period of time. A time series shows the amount of a specific species detected by the mass spectrometer vs. time. Here, this time series for CADO data shows how much organics is present in each sample injection (spike in the graph). The number above the spikes indicate the number of individual sample set.

t_series

The second picture shows a mass spectrum of organics for one sample, which shows its chemical composition and relative intensity of each constituents. By studying the spectral information, we may learn the probable major sources of the aerosol species. Take this spectrum of CADO069 sample as an example. It is marked by a high intensity of CO2 and CH3SO2 species. A strong CO2 signal usually indicates that the sample is relatively more oxidized, while the CH3SO2 spike represents a tracer for a marine aerosol sources (probably comes from algae in the sea).

mass_spec

The third step of data processing focus on elemental information, which may tell us to what extent the aerosol is oxidized. We can achieve this goal by studying and comparing the H:C and O:C ratios of the sample matter. Then we are not only able to determine what kind of functional groups dominate the aerosol sample, but also deduce the sources of aerosols and the kinds of chemical processes the aerosol organics went through in the atmosphere. If you look at the third picture, which also describing CADO069, it tells you what organic functional groups in relatively richer in this sample by comparing the H:C and O:C ratios.

ele_analysis

The analysis above are performed using the Igor program that is designed to perform high-resolution analysis on aerosol mass and elemental information. Such basic analysis would be performed on every sample set I would receive further during this summer. Hopefully, some new data sets will arrive within two weeks. For the following week, I will perform quantitative analysis on current data set. And if time allows, doing some literature search on specific mass spectroscopic tracers for different aerosol sources.

 

Comments

  1. This sounds like a really neat research project! Researching these chemical compositions in the atmosphere is an incredibly important thing to do, considering their potential contributions to climate change, ozone depletion, urban smog, etc. I also had not known that comparing H:C and O:C ratios helped to determine the extent to which the various organic compounds have been oxidized. I notice you mentioned that you were able to “deduce the sources of aerosols”, but I was wondering what some of those specific sources were, and how they could be linked to specific chemical compounds. I was also wondering how these preliminary findings compare with other major cities throughout the world. Is that something you have looked, or will be looking, into?

  2. Thank you for your substantial comments! Some typical sources of aerosols can be anthropogenic, like burning of fossil fuels, and natural, such as emissions of organics from plants and biomass burning. Aerosols come from different sources can have different organic composition, and I am trying to do is to characterize the sources of the aerosol samples I have. Moreover, by studying and comparing the sample data from different cities, I can hopefully have a preliminary understanding on what kind of aerosols dominates the air of each city. Such knowledge is important considering the public health issue and that is something I definitely will be looking more into.

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