Particulate Monitoring

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Particulate Monitoring

Particulate Monitoring

Nephelometers are used in a variety of particulate monitoring studies. Nephelometers are valuable in monitoring changes in particulate matter in real-time due to the instantaneous monitoring of light scattering. The ability of nephelometers to both instantaneously monitor data, as well as record changes in the size distribution of particulates make it ideal to use for source apportionment studies. Nephelometers are also used in wood smoke studies and in comparisons to real time particualte monitors such as BAM's and TEOM's.

It is also possible to perform basic source apportionment work using data generated by the Aurora Nephelometer as although the scattering coefficient to mass factor CoefScat/PM isn’t logged by the Aurora Nephelometer it is output from the Aurora’s RS232 port and can also be backward calculated by comparing PMBAM with PMaurora on an hourly basis.

A shift in this factor indicates that the aerosols chemistry has changed and for instance marine air is now being measured instead of urban air. This information can be useful in estimating the degree of harm that PM concentrations may cause to human health as urban air may pose significantly higher risks than marine air.

Using Nephelometers to provide near real time fine particulate estimates
For use in air quality forecasting and pollution curtailment actions
In the Puget Sound area

The Puget Sound Clean Air Agency is responsible for providing air quality services to the 3.5 million residents living near the Seattle, Tacoma and Everett areas. Fine particulates dominate the aerosol and present the most significant challenges impacting public health and EPA’s standards.  The highest PM 2.5 concentrations occur in the late fall and winter seasons.  These conditions occur in residential areas where the use of wood burning devices is a common source of home heating.  During periods of stagnant meteorological conditions wood burning routinely creates unhealthy air quality necessitating the issuance of temporary control measures call Burn Bans.  Continuous particulate monitors play an essential role in helping the Agency to track diurnal pollution levels, issues public air quality forecasts and make timely decisions to curtail wood burning.

The Agency is recognized as a national leader in the use of Nephelometers in ambient air monitoring. Nephelometers, when correlated with EPA’s Federal Reference Method (FRM) provide a cost effective, reliable and valued added PM 2.5 data source. The technology provides a high temporally resolved indication of rapidly changing pollution levels often seen when people heat homes with wood.  One hour averages correctly show near real time emissions and running twenty hour averages show when pollution relative to EPA’s standards and Washington State trigger levels for issuing curtailments.  In 2006 the Agency began transitioning its network to ECOTECH Nephelometers to benefit from improved engineering, service and support.  According to Mike Gilroy, Meteorologist and Manager of Technical Services, “Once you understand the real strengths of Nephelometry and these easy to operate devices, it is very difficult to see our network meeting operational expectations without their data”.

A Spatial Model of Urban Winter Woodsmoke Concentrations

Timothy Larson, Jason Su, Anne-Marie Baribeau, Michael Buzzelli, Eleanor Setton, and Michael Brauer

In many urban areas, residential wood burning is a significant wintertime source of PM2.5. In this study, we used a combination of fixed and mobile monitoring along with a novel spatial buffering procedure to estimate the spatial patterns of woodsmoke. Two-week average PM2.5 and levoglucosan (a marker for wood smoke) concentrations were concurrently measured at up to seven sites in the study region. In addition, pre-selected routes spanning the major population areas in and around Vancouver, B.C. were traversed during 19 cold, clear winter evenings from November, 2004 to March, 2005 by a vehicle equipped with GPS receiver and a nephelometer. Fifteen-second-average values of light scattering coefficient (bsp) were adjusted for variations between evenings and then combined into a single, highly resolved map of nighttime winter bsp levels. A relatively simple but robust (R 2 = 0.64) land use regression model was developed using selected spatial co-variates to predict these temporally adjusted bsp values. The bsp values predicted by this model were also correlated with the measured average levoglucosan concentrations at our fixed site locations (R 2 = 0.66). This model, the first application of land use regression for woodsmoke, enabled the identification and prediction of previously unrecognized high woodsmoke regions within an urban airshed.

Source: Environ Sci Technol. 2007 Apr 1;41