With the new greenhouse gas reporting rule in place and all the talk about carbon footprints, companies need a roadmap of what exactly CO₂ reporting entails and how to go about collecting and calculating data.

To begin, operational boundaries must be defined by identifying and categorizing core emissions. Broadly speaking, core emissions can fall into two major categories: direct or indirect. Direct emissions originate from sources owned or controlled by the company, such as boilers, chemical products or vehicles. Whereas indirect emissions are a consequence of the company's activities, but actual emissions occur at sources owned by another company. Purchased electricity is an example. There are optional (non-core) emissions that may be included as well, such as transportation of purchased materials, waste disposal, employees commuting to work, etc.

With the scope of monitoring established, the amount of data collection may seem insurmountable. Internal inventory-management plans can assist in organization and delegation of responsibility to maintain accountability. Moreover, a robust environmental management system helps with the overwhelming recordkeeping, tracking and calculating a carbon footprint.

Establishment of a base year is required for proper emission comparisons to be done over time. A base year is the most recent year for which data is available; keeping in mind the purpose is to assess company progress toward emission reduction. Of course, a company may undergo structural changes over time, such as acquisitions or divestments, so adjustments to the base year must be done to keep the comparisons accurate.

Calculation approaches will vary based on the data collection monitoring system. Most often, emissions are calculated with mass balance and/or emission factors. Emission factors can be from relevant published sources, such as EPA's AP-42, or they can be the result of source-stack testing. Note: Even if monitoring is not possible, accurate emission data can be calculated using fuel usage data.

Choosing the right emission factors and equations for different types of sources will be integral for proper calculation but which ones should be used and when?

A. Stationary and mobile road sources: emission factors can be found via the EPA's WebFIRE at http://cfpub.epa.gov/webfire.

Emissions p,s = A s × EF p,s
where, p = Pollutant; s = Source Category; A = Activity Level; EF = Emission Factor

B.Non-road mobile sources (e.g. forklifts) emission factors are obtained through using EPA's Non-road model. This model is designed for "professional mobile source modelers" and can be cumbersome to use as its calculations take many parameters into account that change from year to year and differ across the U.S. However, if only calendar-year averaged emission factors based on the nationwide default mix of parameters is needed, then request a table of reporting-year specific emission factors from the Non-road help desk (for more information visit: www.epa.gov/otaq/nonrdmdl.htm).

Emissions p,s = A s × EF p,s
where, p = Pollutant; s = Source Category; A = Activity Level; EF = Emission Factor

C.Electricity purchased/used emission factors for a facility in the U.S. can be determined by using facility eGRID subregion from the map in Figure 1. If not sure of a facility's sub-region, use the EPA Power Profiler tool (available at www.epa.gov/cleanenergy/powerprofiler.html) to find the sub-region based on its zip code. Then find the appropriate emission factors for CO₂, CH₄, N₂O. Once emission factors have been obtained, use the formula below to calculate emissions:
CO₂ Emissions (tons) = Electricity Use × Emission Factor ÷ 2,204.62 (MWh) (lbs CO₂/MWh) (lbs/metric ton)

D.VOC oxidizers are routinely left out of carbon footprint calculations because component gases differ. Facilities normally have the amount of gas (VOC) burned and the mole fraction of the different components present in the gas stream.

To calculate the CO₂ emissions for each VOC component:
CO₂ Emissions (Metric tons) = [VOC Component (kg) x Carbon Content x Fraction Oxidized x (MW CO₂/ M.W. Carbon)] / (1000kg /Metric tons) where

• Mass of carbon for each VOC component = number of carbons present in the molecular formula of component times 12
• Carbon content = Mass of carbon/ mass of component as a whole
• MW CO₂/ MW carbon (a given standard) = 3.67

For example: Toluene (CAS#: 108-88-3) (Molecular formula: C₇H₈) (Mass: 92)
Assume a 12,000 kg toluene emission through the stack and 99-percent oxidizer efficiency.
First, calculate carbon content based on number of carbons in toluene: (7x12) / 92= 0.9130
Next, calculate CO₂ Emissions from Toluene oxidized:
[12,000 kg x (0.9130) x .99] / 1000 = 10.85 m tons

After final emission data has been quantified for the six greenhouse gases (GHG) of concern CO₂, CH₄, N₂O, SF₆, HFCs and PFCs); their emissions must be converted into a CO₂ equivalent (CO₂ -eq). This is done by multiplying their emission by their unique Global Warming Potential (GWP) for each GHG, which relates to their ability to trap heat in the atmosphere relative to CO₂. An example is shown below:

Example GHG inventory:

• 7,000,000 tons/yr of CO₂ emissions (GWP of CO₂=1)
• 400,000 tons/yr of CH₄ emissions (GWP of CH₄=21)
• 700 tons/yr of N₂O emissions (GWP of N₂O =310)

Total CO₂-eq = tons CO₂ (GWP [CO₂]) + tons CH₄ (GWP [CH₄]) + tons N₂O (GWP [N₂O]) =

7,000,000 (1) + 400,000 (21) + 700 (310) = 15,617,000 metric tons CO₂-eq

In taking on an endeavor such as this, several concepts must be kept in mind to ensure success: relevance, completeness, consistency, transparency and accuracy. For a facility's carbon footprint to be relevant means that it leads to wiser decision making. But how relevant would that report be with out completeness of data that was compiled? For accurate comparisons between years, consistency of methodology and approach is required to compare like with like. Transparency indicates the ability to maintain credibility of internal and external review. Lastly, all of the above is meaningless if accuracy of the data is lacking. This is why a good environmental management system can be invaluable to an organization. It will insure completeness, consistency, transparency and accuracy, which are four out of the five requirements for successful GHG recordkeeping.

So, what's next? Set GHG reduction goals. With the base year emission and current year emission data in hand, a facility can build a reduction plan. Also, remember that portions of the carbon footprint can be used to satisfy the new GHG reporting requirements that are already in place, with report submissions for RY2010 due in March 2011.

If a full carbon footprint is not yet required, why bother? Companies that have committed to tracking and reducing their footprint have enjoyed the benefit of: lowering operating/manufacturing costs; meeting demands of shareholders and investors; enhancing their image, reputation and brand recognition. PE