Week 1 Introtolca-Lecture Notes-Lecture Notes

Lecture Notes for How Green is That Product? 2014 Northwestern University.

How Green is That Product?

An Introduction to Life Cycle Environmental Assessment

Coursera Lecture Notes

January 2014

Prepared by:

Eric Masanet and Yuan Chang

Northwestern University, Evanston, IL, USA

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About these lecture notes

There are many useful resources for learning the life-cycle assessment (LCA) methodology, including

books, websites, case studies, publicly-available lecture materials, and LCA standards and

guidebooks. Rather than choose one particular resource as the assigned reading, the course staff

has prepared this compendium of lecture notes, which will serve as your primary reference for this

course. These notes make use of elements of key online LCA resources that are available to

students, and refer you to them where appropriate for additional information on different LCA

topics. Additional readings will be assigned or suggested throughout our MOOC as part of the

homework assignments, through the discussion forums, and when discussing specific LCA case

studies.

The lecture notes consist of 27 chapters, where each chapter corresponds to a single video lecture.

The first section in each chapter contains a full transcript of the video lecture. These transcripts will

allow you to read along with the lectures as you watch them, to write down comments at different

points in a lecture, and to refer to the lecture content when you are offline.

In many chapters, a second section has been provided, which contains additional notes that expand

upon points made within the lecture and refer you to other LCA resources as appropriate. Because

Coursera video lectures are inherently short, weve made use of the additional notes section to

provide you with supporting information that couldnt be included in the video lectures due to time

constraints. Within the transcript section, youll see blue arrows in the left hand margin that look

like this:

This symbol indicates that additional notes have been provided that expand upon a key point that

has been made during the lecture. Each additional note has been assigned a number, which also

appears in the blue arrow symbol (in our example above, this number is 1.1). The numbered blue

arrows will allow you to easily jump back and forth between the transcript and the additional

information that is relevant to a particular topic.

We hope these lecture notes can serve as a basic, useful reference for you in your learning

experience. Suggestions for improving or expanding these lecture notes for future offerings of this

course are heartily welcomed.

We hope you enjoy our journey together learning about and applying the LCA methodology. Lets

get started!

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Lecture 1: The life-cycle perspective and course goals

Transcript

Hello, and welcome to How Green is that Product? An Introduction to Life Cycle Assessment. Im

Eric Masanet, and Ill be your instructor for this course. I hope youve been looking forward to this

as much as I have.

This course will provide you with a basic working knowledge of life cycle assessment, or LCA for

short. Now, you wont become a certified LCA practitioner in only nine weeks. However, you will

learn how to construct LCA studies that provide transparent results, to build basic LCA models in

spreadsheets, and to collect, analyze, and interpret environmental data in a structured manner for

better decisions.

But perhaps most importantly, youll learn that -- whatever the product -- everything has

environmental impacts and that understanding these impacts requires sound data and thorough

analysis. If you stick with me, youll be equipped with the basic skills to conduct such analyses and

begin answering environmental questions of your own.

So what exactly is LCA? LCA is a method to assess the environmental impacts of a product, process,

or service that involves four major steps:

1. Determine the goals and scope of the LCA;

2. Compile an inventory of energy and material

inputs and environmental outputs across all

relevant life cycle stages;

3. Evaluate relevant environmental impacts

associated with the life-cycle inputs and

releases; and

4. Interpret the results to lead to a more

informed decision.

Lets first discuss what is meant by life cycle stages using this plastic bag as an example. In this

course, well refer to five distinct stages of the product life cycle:

1. Raw materials acquisition, which includes processes related to raw materials extraction and

refining. For our plastic bag, which is made of a plastic called high-density polyethylene or

HDPE for short, raw materials acquisition would include extracting natural gas and

transporting it to a chemicals plant.

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2. Manufacturing, which includes processes that convert raw materials to finished products.

In our case, plastic bags are manufactured by producing plastic pellets, melting them into a

film, and forming the bags.

3. Distribution, which includes transporting and stocking products for consumption. For

example, our plastic bag will be shipped from the manufacturer to a grocer.

4. Use/reuse, which is the stage where products perform a useful service to the consumer. In

our case, the plastic bag will carry our groceries home. Some consumers might also reuse

the bag for additional shopping trips or as a garbage can liner, which is why we often include

reuse in the use phase as well.

5. Stage 5 is the end of life stage, where products enter the waste management system.

Depending on local waste management practices, the plastic bag might be recycled,

landfilled, or incinerated to generate energy.

So what is meant by relevant impacts? As youll learn in this course, an environmental impact is an

adverse consequence associated with inputs of resources and outputs of pollutants across the

product life cycle. For example, the combustion of diesel fuel in the trucks that transport plastic

bags to the grocer releases carbon dioxide, which leads to global warming. When conducting an

LCA, we strive to include all non-negligible impacts so that informed decisions can be made and any

tradeoffs between impacts are made explicit.

Consider again this plastic bag. Many jurisdictions have banned plastic

bags at grocery stores in an effort to reduce litter. However, several

LCA studies have shown that if consumers shift to paper bags, more

diesel trucking might be required. Why is that? Its because a paper

bag takes up more space than a plastic bag, and therefore more trucks

might be required to bring the same number bags to the grocer. So in

this case, one tradeoff of a shift from plastic to paper grocery bags

might be that plastic litter is reduced but diesel fuel use and emissions

are increased.

This case teaches us two important lessons. First, an LCA can reveal that, while we think were

making a green choice, environmental impacts may shift based on the consumption choices we

make. Thats why its important to consider all relevant impacts in an LCA; otherwise such shifts in

impacts might be missed when were evaluating our options. Second, consideration of all life cycle

stages allowed for identification of unintended consequences. That is, a reduction in plastic litter in

the end of life stage might come at the cost of increased diesel fuel use in the distribution stage. If

we just focused on non-biodegradable litter, surely paper bags would look greener than plastic. Its

only by looking at all life cycle stages did we see that paper bags might make things worse in the

distribution stage. So you see that even the simple case of plastic versus paper bags involves

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environmental tradeoffs. With proper application of the LCA method, however, these tradeoffs are

made visible so we can make the most informed decisions.

You may be wondering how LCA is used in the real world, or, more directly, how you might use LCA

after completing this course. If youre an engineer, LCA can help you choose materials and design

features that lead to greener products and technologies. If youre a policy maker, LCA can help you

design public policies and incentives that improve sustainability without simply shifting

environmental problems from one type of impact to another. If youre a consumer, LCA can arm you

with data and results that guide you to greener purchasing decisions. And no matter what you do,

LCA can give you a healthy degree of skepticism of the environmental claims that are so often made

without hard data and through analysis to back them up.

Lets wrap up with an overview of what you can expect. Each lecture will

introduce a new concept, which will be reinforced through online quizzes,

homework, and the course notes. I believe LCA is best learned by

jumping in hands on, so in this course youll build an LCA model of a

simple product that you should all be familiar with a bottle of soda. No

special LCA software packages will be required; all that is needed is a

spreadsheet.

Each week youll be developing a new section of the model that relates to

that weeks lecture material, so by the end of the course youll have built

a complete bottled soda LCA. While the product is fairly simple, by

building the model across all life cycle stages and impacts, youll acquire the skills and perspectives

that should allow you to move on to more complex products after you complete this course.

Lastly, well also occasionally offer separate videos describing real-world LCA studies that highlight

key material, so you can easily see how the theory relates to practice in real time.

Im looking forward to this experience together. See you next time!

Additional notes

Starting in week 3, youll begin building your very own LCA model of a bottle of soda packaged in

plastic. See the Course Project section of the course website for more details! (The Course

Project section can be accessed by clicking on Start Here! or Course Information in the left

hand navigation pane on the course website.)

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Lecture 2: Understanding unit processes

Transcript

Welcome back! Today well begin learning about the data structure of an LCA, starting with LCAs

most fundamental building block: the unit process model. But first lets quickly review what we

learned yesterday.

The product life cycle can be divided into five major stages: raw materials acquisition,

manufacturing, distribution, use, and end of life. In our plastic bag example, we learned that raw

materials acquisition covers the extraction and transportation of natural gas, which is then

converted into ethylene. Ethylene is converted into HDPE and formed into a bag in the

manufacturing stage. Next, the bag is distributed to retail stores, where it is filled with groceries to

transport food home during the use stage. Lastly, at the end of life stage, the bag is either recycled,

landfilled, or incinerated to generate energy.

We also learned that a key step in all LCAs is to compile an inventory of energy and material inputs

and environmental releases across all relevant life cycle stages. So how do we compile such

inventories? We do so by modeling the product life cycle as a series of unit processes. The ISO

14040 standard for LCA defines a unit process as the smallest portion of a product system for which

data are collected when performing a life-cycle assessment.

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This is a picture of a generic unit process. On the left we have inputs of materials and energy

required to generate a useful product output. On the right we have the outputs of environmental

emissions and co-products that are associated with the process, along with the product output

itself. From now on, well refer to the inputs and outputs associated with a unit process as the unit

process inventory, which is a term commonly used by LCA practitioners.

To visualize how we use unit processes, lets look more closely at the manufacturing stage of our

plastic bag. The first step is to process natural gas into ethylene, which well represent by this first

unit process model.

The second step is to convert ethylene into HDPE pellets, which well represent with this second unit

process.

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The third step is to melt the HDPE pellets, extrude a film, and form the bags in the bag production

process.

As youve probably guessed, to construct a complete LCA model for the plastic bag, wed need to

develop and apply unit process models to capture all unit processes at each life cycle stage. We can

then sum all the unit process inventories to quantify the total environmental footprint of the bag life

cycle. Youll learn how to do this later; for now, you may be asking yourself how such unit process

inventories and life-cycle models can be developed without detailed engineering knowledge.

Fortunately, we have we have databases and literature sources to help us in this regard.

For example, a unit process inventory I obtained from the literature for converting ethylene to HDPE

pellets looks like this. If this level of detail seems a bit daunting, dont worry youll learn how to

work confidently with unit process inventory data in this course.

Fortunately, the LCA community has adopted a number of conventions for organizing unit process

inventories to make our lives easier. These conventions help ensure that inventories are intuitive

and use the same data structure for easy transfer between researchers and databases. So while the

unit process inventory for HDPE pellets may look complicated, thanks to this structured organization

of data it is actually simpler than it looks.

2.2

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First, many unit process inventories refer to inputs and outputs as flows or exchanges. In this

course, well use the word flows. Unit process inventories are essentially comprised of flow

information listed in rows.

In many LCI databases, flows are further characterized as flows to or from nature or to or from the

technosphere. In this course, well adopt this convention and organize our inventories into the

following four types of flows:

1. Inputs from nature,

2. Inputs from the technosphere,

3. Outputs to nature, and

4. Outputs to the technosphere

Inputs from nature are probably pretty obvious: they refer to flows such as crude oil extracted from

the ground or corn harvested from a field. Conversely, outputs to nature refer to pollutants and

wastes that are released back into the environment. Inputs from and outputs to the technosphere

refer to any flow of energy or mass that originates from a man-made process. For example, diesel

fuel is produced from crude oil in a petroleum refinery, but we dont find diesel fuel occurring

naturally in the environment.

For our plastic bag, the extraction of natural gas describes a flow from nature. In the next unit

process, that natural gas is converted to ethylene. Here, because the natural gas came from a pipe

and not the ground, it is considered an input from the technosphere. Because ethylene is an

intermediate product that is used by other unit processes, it is considered an output to the

technosphere.

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Why do we need to distinguish between flows to and from nature and flows to and from the

technosphere? Besides helping us better visualize the origins and destinations of flows in our

inventory, identifying flows to and from nature allows us to quantify environmental impacts in the

life-cycle impact assessment step of an LCA. Well learn more about impact assessment later in the

course. For now, lets get used to organizing our unit process inventories in this way.

Lastly, well use SI units to describe all flows in our unit process inventories in this course. For

example, mass will be expressed in grams, energy in joules, and volume in liters. Some of you may

wish to review the SI system before proceeding with this course; further readings are provided in

this weeks course notes.

Additional notes

The ISO 14040 series of standards are a set of best practice rules and guidelines for conducting

LCA that have been developed and revised by the international LCA expert community since the

1990s. Well be referring to these standards often throughout the course. Well use them as a

useful way to discuss the step by step nature of an LCA and to reinforce best practices.

Unfortunately, the actual standards documents are not freely available to the public. However,

youll get a basic understanding of these standards through our class materials and through the

additional readings well suggest and assign. There is no need to purchase the standards to benefit

from the content of this course.

For those of you who would like to learn more about the formal standards, please visit the

International Organization for Standardization (ISO) website at:

http://www.iso.org/iso/home/store/catalogue_tc/catalogue_tc_browse.htm?commid=54854

To give you a sense of the detail contained in a typical life-cycle inventory (LCI), and the

documentation that explains and supports such inventories, take a peek at the following report.

Youll use some of these data in this course to build you spreadsheet LCA model of a bottle of soda.

There is no need to read this report now, or to understand its contents. But looking it over will give

you an idea of the types of information sources that we rely on when constructing LCA models.

Franklin Associates (2009). Life Cycle Inventory of Three Single-Serving Soft Drink Containers:

Revised Peer Reviewed Final Report. Prepared for the PET Resin Association. Eastern

Research Group. Prairie Village, KS. http://www.container-recycling.org/assets/pdfs/LCA-

SodaContainers2009.pdf

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2.2

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There are many useful resources online for reviewing and practicing conversions from Imperial and

US Customary units into International System (SI) units. While well use SI units in this course, you

are likely to encounter data sources in your project and in your LCA careers that are expressed in

Imperial and US Customary units instead of in SI units. Here are some conversion resources that the

course staff recommends. Do you know of other good resources on unit conversions? Recommend

them to your classmates in the discussion forum!

International System of Units from NIST. Essentials of SI units, background, and

bibliography. http://physics.nist.gov/cuu/Units/

A concise summary of the International System of Units from BIPM.

http://www.bipm.org/utils/common/pdf/si_summary_en.pdf

OnlineConversion.com Convert just about anything to anything else.

http://www.onlineconversion.com/

2.3

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Lecture 3: Constructing unit process inventories: Part 1

Transcript

Welcome back. In todays lecture, well dive deeper into how unit process inventories are

structured for ease of interpretation and ease of transfer between researchers and databases. Last

time I introduced the four types of flows well use in our inventories:

1. Inputs from nature,

2. Inputs from the technosphere,

3. Outputs to nature, and

4. Outputs to the technosphere

Lets take a closer look at the complete unit process inventory for converting ethylene to HDPE

pellets. Ive created this inventory in a spreadsheet in the same way that youll be creating unit

process inventories in your spreadsheets. As we discussed last time, flow data appear in rows of the

inventory table, and they are organized into our four types of flows. In this course, the first column

in the inventory will always contain the flow type, starting with inputs from nature, followed by

inputs from the technosphere, outputs to nature, and outputs to the technosphere.

The second column will always contain the name of the flow, which, by convention, uses standard

names for products (e.g., diesel fuel), pollutants (e.g., carbon dioxide), and resources (e.g., water).

In many cases, the name of the flow will be taken directly from the LCI database from which we get

the flow data. It is critically important to use standard flow names and to use them consistently so

we can link up unit process inventories correctly when creating our LCA model.

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The third column contains additional information on the origins and destinations of flows to and

from nature, which well refer to in this course as the flow category. Inputs from nature will

always be denoted as resources in the category column, while outputs to nature will be denoted

by the medium to which they are released. There are three media well denote: air, water, and land.

The fourth column is reserved for subcategories of the third column. For example, the

subcategories for outputs to air include emissions to areas with low population density and

emissions to areas with high population density. And the subcategories for resources include

resources extracted from in the ground (like coal), from water (like drinking water), or from the

biosphere (like wood). In this course, well use a standard set of subcategories to describe inventory

flows. Ive provided the list of subcategories well use in the lecture notes because there are too

many to mention here.

Why do we need information on flow categories and subcategories? The main reason is that this

information helps us better quantify the environmental impacts caused by flows to and from nature

in the life-cycle impact assessment step of an LCA. For example, you might easily imagine that a

pollutant emitted in a high population density area will have a higher human health impact than if it

were emitted in a low population density area where there are fewer persons exposed. Well learn

more about impact assessment later in the course.

I also want to mention that in many LCI databases, flows to and from nature are referred to as

elementary flows. So you arent confused by this, moving forward well also use this label for our

flow types in unit process inventories.

By convention, well always use the category product for flows to and from the technosphere.

This makes sense when we consider that once a resource enters the technosphere, it is converted

into different forms of products for further use by industry and society.

The fifth column in our inventory table will always contain a numerical value and our sixth column

will always contain the unit in which that value is expressed. Where do these values come from?

Typically through some combination of direct measurement, engineering estimation, or literature

sourcing. Knowing where the data come from and how to determine their quality is a critical step in

any credible LCA, and one which well discuss later in this course. For now, just assume that all data

in our inventory come from reliable sources.

The numerical value expresses the amount of each flow that corresponds to the units of product

output listed in the inventory. For example, our product output is one kg of HDPE pellets, and the

emissions of CO2 to air associated with the production of one kg of HDPE pellets is 100 g CO2.

Here the product output is expressed in units of mass; however, the product output in a unit process

inventory can be expressed in many different units depending on what goods or services are

provided. The unit process of pellet production logically has product outputs expressed in units of

kg, which corresponds to physical production. However, a unit process for a diesel freight truck

might have product output expressed in units of kilogram-kilometers, which corresponds to the

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useful service provided by trucking. Or a unit process for electricity production might specify kWh of

electricity produced, which is the useful output of that process. Youll get exposed to all of these

types of outputs and more moving forward.

Lastly, our simple example inventory focused on single unit process, but youll often encounter unit

process inventories that combine several unit processes into one aggregated inventory. For

example, rather than finding every unit process step in the manufacture of the bag which would

include natural gas extraction, transportation, conversion to pellets, and bag forming you might

just find a single inventory for all of these processing steps combined. This aggregated inventory

would contain the sum of all included unit process flows.

Aggregated inventories are quite common in practice, because they can simplify a complex chain of

processes for general use. Aggregated inventories also protect private entities who may not want to

release detailed unit process data on each step in their production chain. The downside is that one

loses visibility on which of the aggregated processes might be hot spots and often the ability to

recreate the inventory using process-level knowledge.

How can you tell if you have an aggregated inventory? Good databases will tell you this in their

inventory documentation. Youll notice terms like cradle to gate, which refers to flows from

nature to a certain point in the technosphere, or gate to gate, which refers to flows between

points in the technosphere. All unit processes included in the aggregated inventory should be listed

explicitly.

Additional notes

Note that this information appears in our lecture notes for Chapter 4 (Week 2). 3.1

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