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Optimized Noise-Reduction Algorithm (ONA) Program Improves Black Carbon Particle Measurements Using Aethalometers

This tool is no longer being updated for newer operating systems nor can EPA provide troubleshooting support. We continue to have this tool available for download to support users who may have compatible operating systems. Please note that MATLAB code for ONA is also available as supplemental information in the science journal publication.

What is the Optimized Noise-Reduction Algorithm (ONA)?

ONA is a program that reduces noise in real-time black carbon data obtained using Aethalometers. Aethalometers optically measure the concentration of light absorbing or “black” particles that accumulate on a filter as air flows through it. These particles are produced by incomplete fossil fuel, biofuel and biomass combustion. Under polluted conditions, they appear as smoke or haze.

Who should use ONA?

Researchers who need to maximize the time resolution of black carbon data from Aethalometers can benefit from using ONA. Applications include personal monitoring, cook stove, and other combustion-related research studies.

What are the benefits of using ONA?

Atmospheric black carbon contributes to adverse impacts on human health. It has been linked to a range of climate impacts. Understanding its sources and prevalence in the atmosphere is key to developing strategies to manage its impacts. We need high-resolution data sets that can detect short-term variability to understand black carbon’s behavior over distance and time.

ONA uses variable time averaging to reduce noise in real-time black carbon data obtained using Aethalometers, while preserving the ability to detect short-term variability. It can be applied to data collected indoors and outdoors, from stationary and mobile platforms. This includes data used to:

  • measure rapidly changing source emissions,
  • quantify outdoor air pollution levels from mobile platforms and balloons,
  • compare time-varying indoor air pollution levels with health indicators, and
  • observe dynamic trends in ambient air quality.

How Does ONA Work?

Aethalometers measure the amount of light transmitted through a filter as particle-containing airstreams move through it. Measurement sensitivity is directly related to the loading rate of the particles on the filter, which is a function of concentration, flow rate and filter area. When sampling at low concentrations or at very high rates (e.g., every second), instrument noise can result in erroneously high or low values. If the magnitude of the instrument noise is high compared to the concentration, negative data can be reported.

The ONA algorithm uses variable time averaging, adjusted based on the loading rate of the particles on the filter, to reduce the noise in real-time Aethalometer black carbon data. This simple approach capably resolves the noise in the Aethalometer data, while maintaining the highest time resolution possible. It also reduces the occurrence of negative data values in lower concentration sampling environments – for all cases tested, the ONA post-processed data have a near-zero occurrence of negative values.

To use ONA, Aethalometer data sets need to include time stamps, black carbon data, and light attenuation values.

Disclaimer: This does not imply EPA endorsement of a commercial product nor a quality review of black carbon data. 


Version 0.0
Release Date August 2011
Development Status General release
Operating System Windows
Development Language MATLAB
Intended Audience Scientific community



Hagler, G.S.W., Yelverton, T.L.B., Vedantham, R., Hansen, A.D.A., Turner, J.R. (2011)  "Post-processing method to reduce noise while preserving high time resolution in Aethalometer real-time black carbon data."  Exit Aerosol and Air Quality Research, 11: 539-546. doi: 10.4209/aaqr.2011.05.0055 

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Technical Contact

Gayle Hagler
EPA Environmental Engineer