Why measuring PPM alone is not enough
Introduction
Our Qube continuous emissions monitoring solution collects data on emissions and environmental conditions 365 days a year. It uses the data it captures to calculate an accurate site rate, indicating the total emissions coming from the monitored site at a given point in time.
How do you measure concentrations of gas?
Concentrations of methane and other gases are often measured in PPM (parts per million), an indication of how much gas is present in an area, but to calculate the site rate, PPM measurements alone are not enough.
While there are many factors that can affect site rate calculations, one of the most notable is local wind conditions. Strong winds can dilute gas concentrations while lack of wind can lead to larger accumulations, both of which will impact results.
How do anemometers improve site rate calculations?
Analyzing wind vectors (wind speed and direction) with an anemometer is one way we can improve our calculations. Wind data is used to understand how a molecule of gas may have travelled before reaching a sensor, and we can use this data to improve our estimates of emissions rates. However, relying on the measurements of one fixed instrument can be misleading. Wind is impacted by atmospheric pressure and local topography such as buildings and equipment. By adding additional anemometers, we can increase the amount of data we collect, giving us greatly improved insights into emissions on site.
Qube Technologies ships an anemometer with every device. Each one measures wind conditions in the immediate vicinity of the sensor and sends the time correlated data to Qube's Emissions Dashboard for analysis. The dashboard combines data from every sensor on the site, painting a complete picture of historical wind patterns.
What is the impact of sensor distance on site rate calculations?
We also know that the distance between a sensor and a potential leak location can impact the PPM reading of methane detected (the further you are from a leak, the less methane you will detect), but by combining extensive wind data with fixed sensor locations, we can compensate for this effect when determining emission rates.
To see how all of this works, lets look at Qube's Emissions Dashboard.
Examples of the impact of wind on emissions quantification
In the example below, you see an operating site with four fixed Qube sensors thoughtfully deployed to account for existing equipment on site (likely leak locations) and for prevailing winds in the area. In the Green highlighted box, you can observe relatively low wind speeds across all sensors, and very high concentrations of CH4 detected by two of the four devices. By analyzing the historical environmental data we collected, Qube is able to determine the site rate, while accounting for wind, distance from sensors, and other environmental conditions.
Using PPM and wind vectors in the calculation of a site rate
In this same example, the red box highlights a spike in the site rate, along with lower detected emissions across all but one of the sensors. Wind speeds increased during this time, leading to higher dispersal of emissions and lower concentration readings, but by applying environmental data to our AI based algorithms, we can infer that the emission rate did not decrease, and likely increased during that period.
Effective quantification of methane emissions
With accurate, live, and historical data on wind and other on-site environmental conditions, Qube can effectively quantify greenhouse gas emissions and produce an accurate site rate for operators. If you would like to learn more about Qube's Continuous Monitoring Solution, contact us today.