Advanced optical spectroscopy methods have gained broad application utility in meeting the challenges of monitoring environmental pollution effectively.
Image Credit: Forance/Shutterstock.com
The world's population has increased significantly over the past century, leading to enormous growth in industrial manufacturing facilities. Pollutant gas emissions into the environment are among the negative byproducts of mass production.
Impact of Pollutants on the Environment
Particulate matter, including dust, dirt, and pollen particles in the air and water, along with hazardous gas mixes, are types of pollutants found in the environment. Methane (CH4), nitrogen dioxide (NO2), carbon monoxide (CO), and carbon dioxide (CO2) are a few examples of dangerous gases.
Combustion activities are the usual source of poisonous gasses.1 Examples of combustion processes include the burning of wood, oil, coal, charcoal, natural gas, and other fossil fuels.
Exposure to excessive levels of air pollution may cause adverse health consequences, such as lung cancer, heart problems, and respiratory infections.
Global warming has been linked to the emission of greenhouse gases, including CO2. CO2 absorbs infrared radiation from the sun and other sources, which is re-emitted in all directions. While a portion of that energy is radiated into space, the majority is focused back onto Earth, leading to increased heat retention when CO2 is produced on Earth.
Optical Spectroscopy for Environmental Monitoring
Optical spectroscopy, broadly described as light-matter interaction, is a powerful method capable of revealing extensive information about a sample when interrogated by light.
Continuous advances in optical spectroscopy techniques have improved how optical spectroscopy can be employed. Information about a sample can be attained based on its characteristics, such as its atomic properties, textural features, and how the sample scatters light.
Some fundamental optical spectroscopy methods include:
Reflection
In reflection spectroscopy, a probe that delivers and collects light is pointed at a sample. This reflection probe delivers light to the sample and collects the back-reflected light to a spectrometer. In a gas mixture, light that is not absorbed but could be reflected can be monitored.
Fluorescence/Emission
In fluorescence or emission spectroscopy, light incident on a sample excites the atoms when photons of a particular frequency are absorbed.2 Subsequently, the excited electrons decay into lower energy levels, emitting different energy photons. A spectrometer collects the fluorescence, which is analyzed to identify the molecules within the sample.
Raman Spectroscopy
Raman spectroscopy is one of the most powerful non-invasive tools available for scientists to identify the structures of arbitrary molecules. The Raman effect was discovered in India in 1928 by future Nobel Laureate Sir Chandrasekhara Venkata Raman.
Incident light on a molecule is scattered in the Raman technique. The majority of scattered light is at the same wavelength as the source and does not offer any meaningful information.
Nonetheless, a small amount of light is scattered at various shifted wavelengths, depending on the chemical makeup of the molecule. This wavelength change is known as the Raman shift and can be used to gain valuable information about the molecule.
Absorption/Transmission
Light entering a sample can also be absorbed at different wavelengths while the rest of the light transmits through the sample. The data collected from such a set-up provides insights into identifying the molecules present in the sample.
All spectroscopic techniques can be used to monitor the environment for pollutants, as depicted in Figure 1 below.
Figure 1: Spectroscopy methods used for environmental monitoring. Image Credit: Ilamaran Sivarajah
Advancements in Optical Spectroscopy
Numerous research efforts have focused on advancing basic spectrometric techniques to enhance performance. Depending on the type of matter investigated and the environmental conditions they are interrogated under, a variation of the method is applied.
For example, surface-enhanced Raman spectroscopy (SERS) is a Raman scattering method that introduces nanoparticles on rough nanostructure surfaces to enhance the detected signal.3
UV Spectroscopy and Laser-Induced Fluorescence (LIF) are methods in which the incident light source is carefully chosen to be within a particular wavelength range. This effort narrows the target species being investigated.
Other techniques, like laser-induced breakdown spectroscopy (LIBS), are prominent tools in sorting recycled materials. Using tunable lasers instead of a white light source further enhances the precision of measurements.
Fourier transform infrared Spectroscopy (FTIR) is another analytical method for classifying organic, polymeric, and occasionally inorganic materials. Infrared light is used in the FTIR analysis procedure to scan test materials and observe chemical characteristics.
The Sentinel series of satellites commissioned by the European Space Agency are deployed to monitor gas emissions in the Earth's atmosphere from space.4 They have highly accurate spectrometers positioned towards the Earth to collect data.
Future Outlook
Optical spectroscopy has become a vital monitoring tool in the global effort to achieve net-zero carbon emissions and achieve environmental sustainability while providing for a growing population.
Continuous research and development efforts are underway to advance the field of spectroscopy, both in terms of instruments and spectrum analysis. New technologies in light sources, sample preparation methods, and detectors are driving ongoing advancement of instrumentation.
Simultaneously, the imperative to capture increasingly detailed spatial and temporal information underscores the growing significance of novel spectral analysis strategies.
More from AZoOptics: Unseen Frontiers: Navigating the Future of Invisibility Technology and Research
References and Further Reading
- Feng, S., Farha, F., Li, Q., Wan, Y., Xu, Y., Zhang, T., Ning, H. (2019). Review on Smart Gas Sensing Technology. Sensors. doi.org/10.3390/s19173760
- Zacharioudaki, DE., Fitilis, I., Kotti, M. (2022). Review of Fluorescence Spectroscopy in Environmental Quality Applications. Molecules. doi.org/10.3390/molecules27154801
- Ong, TTX., Blanch, EW., Jones, OAH. (2020). Surface Enhanced Raman Spectroscopy in environmental analysis, monitoring and assessment. Sci Total Environ. doi.org/10.1016/j.scitotenv.2020.137601
- The European Space Agency. (no date). Sentinel-5. [Online] Sentinel Online. Available at: https://sentinel.esa.int/web/sentinel/missions/sentinel-5
Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.