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Basic air quality statistics

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What is the meaning of air quality statistics? Where is statistical data used in the air quality business? If we define the two components of the concept, we can then put them together to see what we come up with.

We start with air quality, the condition of the air. This may include temperature, speed of motion and pressure, and, most often, the composition of the air.

Composition normally means the humidity and/or the degree to which the air contains pollution. And pollution? Well, potentially-polluting contaminants, really.  

The air contains dust, chemicals or germs that may alter the lives or health of people and other living things or the condition of the environment.  If it happens a lot and in high amounts, we call that air pollution.

Now what about statistics? This branch of mathematics deals with numerical data: how to gather it, how to interpret it, what kind of inferences can be made from it.

We can also present and explain it and design ways to improve our sampling (data collection) techniques and efficiency. We use statistics in business, government, social sciences such as population studies and physical sciences such as chemistry and meteorology.

So air quality statistics is a collection of mathematical data pertaining to meteorology and, more often, air pollution. Therefore air quality statistics is a common concept in the field of environmental studies.

What kinds of air quality statistics do we need?

When designing plants and seeking government approval, oil and gas companies often receive stipulations that air quality is to be monitored for a number of potentially contaminating species such as H₂S, SO₂ and NO₂.  The directive outlines methods used measure air quality, the air quality statistics required including sampling types and frequencies as well as results in tabular or graphical form.

They seek representative and outlier data points, "durations and frequencies of non-median events," for instance. Here is a database of the air quality collected for one region: http://www.casadata.org/ - many other parts of the world will have some of this type of data available to the public as well.

Another example: New gas plants need to incorporate a surface water runoff management plan into the plant design and facility operation in many jurisdictions. If there are any creeks or rivers, nearby runoff water shall be contained using a design that considers terrain, soil characteristics and rainfall data, along with any input from neighbours into account.

These criteria are used in the Province of Alberta Code of Practice for instance - According to the Alberta government, the plant operator must use a runoff management plan in the facility design. The plan shall consider the soil shape, location and absorption characteristics as well as meteorological statistics (for example, rainfall) and other possibilities for contamination. It considers where surface water will go and what effects it will have.

Emissions Inventories

In Canada, as in other countries, federal agencies take on the responsibility for air quality statistics that would affect other parts of the world. Examples of this include the National Pollutant Release Inventory (NPRI) from which a nation-wide database of contaminant releases is compiled for internal and authorized uses.

Most countries, Canada included, keep tabs on the amount of greenhouse gases (GHG) emitted by major industrial facilities. This air quality data will likely come in handy for establishing a baseline for carbon trading programs.

Professionals who assess leaks and fugitive emissions use a variety of methods for incorporating air quality statistics. They can use the US EPA Method 21 for instance to complete their estimates. Here, a hand-held device detects point-source leaks. Once the leaks get counted and classified, total plant emissions can be generalized by mathematical manipulation.

If a plant wants to use their own correlations for each unit for greater precision, they may be advised to take the results with some skepticism, as the relationship used for a specific component might not be the same in varying applications (industries). Regulating bodies such as the Canadian Association of Petroleum Producers (CAPP) may provide specific instructions in how to handle these types of evaluations.

Why bother with statistics?

Statistical methods are about saving time as opposed to counting and cataloging every item. Another short cut using air quality statistics in leak inventorying is the use of three-stratum emission factors, where we define three ranges and slot the activity (leaks in this case) into the most appropriate one, then deal with them all in an aggregrate fashion. We apply one equation to the entire group.

Leak-rate correlations give us a quicker way to get leak rates, and it generally gives better results for natural gas leak detection than many other emission-factor techniques. It incorporates a logarithmic relation between the leak rate in mass emitted per unit time to a series of calibrated and measured values. Published values standardize the quantifying work and are easier to research and understand.

Some production facilities prefer to use values assigned to each of the plant units considered instead. Any claimed improvements in accuracy may or may not be true as consistency of application is more complicated to assess. This option tends to be more costly and inefficient as well.

A statistical approach to processing large bodies of data helps streamline the operation significantly. Air quality can present the world with one of its largest bodies of data.

This consulting firm, Calvin Consulting Group Ltd., can help you with your data. Please call Barry Lough at at 403-547-7557.  Personally, I specialize in the air dispersion modelling department.

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