How much carbon dioxide does a person produce and how does that compare to our cars?
One of the more interesting questions I've had during a talk in some time. Maybe not from the answer, but because it leads to some other rich areas including, perhaps, your mental efficiency at home and in the office.
The simple answer is about a kilogram a day.. we breathe in air which has some oxygen in it. There are tiny chemical factories in our cells called mitochondria that manage a neat trip - cellular respiration, which is the rough inverse of photosynthesis. They take carbohydrates and oxygen and produce energy with carbon dioxide and water was by products. This energy is what keeps us alive.1 For example:
C6H12O6 + 6O2 -> 6O2 + 6H2O + energy
For an average adult who uses about 2,000 Calories a day we get close to one kilogram of carbon dioxide a day.2 So now we can take on the car comparison. In a year the population of the US produces about 300 million * 365 days * 1 liter/day ~ 110 billion kg of CO2. Last year Americans burned about 134 billion gallons of gasoline. Burning a gallon of gasoline releases about 8.8 kilograms of CO2, so automotive use releases about 1180 kilograms of carbon dioxide into the atmosphere. Our cars emit about ten times as much carbon dioxide into the air as we do. Of course most of the world doesn't drive as much as we do, so the average world figures would be much closer. It begs the question of how important are cars relative to humans?
The answer is easy at the surface. People get their energy from recent photosynthesis. It may pass through a cow or a chicken on its way to your body, but it probably came from a recent plant that is either still alive or has been replaced. It is part of the carbon cycle the Earth is currently tuned to handle. Most of the gasoline comes from oil which is a carbon storage source that has been sequestered for millions of years. We are releasing carbon dioxide into the air that is beyond what the carbon cycle can handle - at least that's the simple explanation.
Looking a bit deeper, and why this question is interesting, we have to ask how much energy was used to get the energy stored in the plant to our fork and where did that energy come from? Sorting that out turns out to be a very complex task. A vegan who eats uncooked plants raised without fertilizers and harvested by hand requires very little excess energy. But our food system is terribly inefficient. It takes an enormous amount of energy to irrigate a field, making fertilizer takes a lot of energy, energy is used to harvest, transport, process, refrigerate and cook our food. Making food from food adds another layer of inefficiency. A steer is a machine that turns plants into meat with a miserable 5% efficiency. Chicken is much better at 10 to 15% and some fish can be very inefficient when the cost of fishing is added.
A bottom line is that our food system is only about 10% efficient overall - an average person requires about 2,000 to 2,500 Calories a day and it takes about 25,000 Calories of energy to produce 2,500 Calories. In country-scale discussions you sometimes encounter the term quad.2 The US population requires about 1 quad of energy from food and agriculture, distribution, cooking etc consumes about 10 quads. Total energy use in the US is about 100 quads - so although people only require one percent to stay alive, it takes ten percent of our energy economy to feed us.
But we exhale enough carbon dioxide to fill about 275 two liter bottles a day - and much that is in a home or office.3 Although carbon dioxide is relatively harmless it can kill if the air you breathe has a lot of it. A reasonable question is what are the effects of normal respiration in a closed environment? Can our bodies handle it?
When AT&T Research moved to the Florham Park, NJ facility I found the air in my office became stuffy and stale when the door was closed. The circulation system wasn't properly adjusted, so I had the building HVAC guy adjust it. His first step was diagnostic - there were any number of chemicals to worry about with carpets outgassing, but it turns out measuring CO2 levels is reasonably inexpensive and is a proxy for many problems, so they left monitor with a chart recorder in my office for a few days. The levels frequently went to over 2,000 parts per million.
It turns out there are any number of suggested standards for CO2 levels, but I don't know about any firm requirements - at least not in New Jersey. At the time it was recommend a close office not exceed 800 ppm. The vents were adjusted and a dead fan restarted taking my office to about 500 ppm with the door closed for hours with a few people in it and a bit over 400 otherwise. Not bad as the atmosphere at the time was about 370ppm (now it is closer to 400). The room now had a breeze, but I felt more comfortable in it.
Recently work has been done looking for better numbers. Just what should a home or office be set to? Ideally one would think about 280 ppm as that is what we have evolved to, but we've blown through that. Is the safe level 500, 600, 700, ... 1,000???
Recent work suggests that you shouldn't go over 600ppm - that one begins to see cognitive issues that get worse with increasing concentrations.4 Confirmation of these results is needed, but other work suggests they may be good enough to take action - after all, no harm is done lowering a level to something closer to the atmospheric background.
Do you know the CO2 levels in your office, your conference rooms, your home...? Just what kind of accuracy do you need to measure it? There are a variety of techniques, but a relatively inexpensive device can be had that is good to about 50 ppm in the range from 100 to 10,000 ppm.
I wonder how many homes and businesses are running with an intellectual handicap? This is particularly important as home and offices become "tighter" and less drafty to save energy. At some point one has to think about ventilation and possibly use a heat exchanger.
When weather conditions and work permits I tend to work outside. Since I turn off my phone this has the added benefit of allowing me to focus on single tasks. Not a bad way to spend portions of the day.
1 Since the carbohydrates ultimately come from green plants which get their energy from the Sun using photosynthesis, it is fair to say that we are ultimately solar powered. There are some conversation and storage steps, but the energy was recently (usually within a year or less) leaving the photosphere of the Sun in the form of visible light.
2 A quad is a quadrillion British Thermal Units. A BTU is yet another unit of energy - 1 Calorie is approximately 4 BTUs
3 One kilogram of carbon dioxide works out to about 550 liters of carbon dioxide gas at standard temperature and atmospheric pressure - a mole of CO2 is 44g, so we have 227 moles of CO2. At 25°C and 1 atmosphere Boyle's law give us about 24.5 liters for one mole of gas. So you would fill about a 275 two litter bottles every day if you wanted to sequester it.
Is CO2 an Indoor Pollutant? Direct Effects of Low-to-Moderate CO2Concentrations on Human Decision-Making Performance
Usha Satish,1 Mark J. Mendell,2 Krishnamurthy Shekhar,1 Toshifumi Hotchi,2 Douglas Sullivan,2 Siegfried Streufert1 and William J. Fisk2
1Department of Psychiatry and Behavioral Science, Upstate Medical University, State University of New York, Syracuse, New York, USA, 2Indoor Environment Department, Lawrence Berkeley National Laboratory, Berkeley, California, USA
Background: Associations of higher indoor carbon dioxide (CO2) concentrations with impaired work performance, increased health symptoms, and poorer perceived air quality have been attributed to correlation of indoor CO2 with concentrations of other indoor air pollutants also influenced by rates of outdoor-air ventilation.
Objectives: We assessed direct effects of CO2, within the range of indoor concentrations, on decision making.
Methods: Twenty two participants were exposed to CO2 at 600, 1,000, and 2,500 ppm in an office-like chamber, in six groups. Each group was exposed to these conditions in three 2.5-hour sessions, all on one day, with exposure order balanced across groups. At 600 ppm, CO2 came from outdoor air and participants’ respiration. Higher concentrations were achieved by injecting ultrapure CO2. Ventilation rate and temperature were constant. Under each condition, participants completed questionnaires on health symptoms and perceived air quality, and a computer-based test of decision-making performance. Participants, and the person administering the decision-making test, were blinded to CO2 level. Data were analyzed with analysis of variance models.
Results: Relative to 600 ppm, at 1,000 ppm CO2, moderate and statistically significant decrements occurred in six of nine scales of decision-making performance. At 2,500 ppm, large and statistically significant reductions occurred in seven scales of decision-making performance (raw score ratios 0.06-0.56), but performance on the focused activity scale increased.
Conclusions: Direct adverse effects of CO2 on human performance may be economically important and may limit energy-saving reductions in outdoor air ventilation per person in buildings. Confirmation of these findings is needed.
Four small items this time:
First Sukie is allergic to chocolate, so I've been experimenting with homemade carob bark and chips ... here is the best effort to date:
You need a first rate carob powder. After struggling with some substandard carob powders I tired the toasted carob powder from Bob's Red Mill. (I also strongly recommend them for grains in general - great quality and consistency plus they are socially responsible). Really excellent stuff!
This gives a bit over 100 grams of carob bar (break it into bits for chips) - scale as you need. Grade A maple syrup has nothing to do with the quality .. rather it is the first draw and tends to be clear and delicately flavored. It is difficult to find in stores (much of it is mislabeled). If you use regular maple syrup, try a lower amount - say half as much, and make up the sweetness with simple syrup)
° 22g toasted carob powder
° 60g coconut oil
° 20g grade A maple syrup*
° 4g finely ground white sugar
° a pinch of salt
° 0.5 tbl vanilla extract
° spay a non-stick coating on a pan that will fit in your freezer (a standard 8x8 cake tin is great)
° Pour the coconut oil into a bowl and heat a bit (I use a microwave on low power) to liquify it. It is usually solid or semi-solid at room temperature.
° mix in the rest of the components .. you may want to start with a bit less sweetener for your first try
° adjust sweeteners
° pour the mixture into the pan and freeze for about 30 minutes
° pop off with a spatula or knife.
You might try a larger mixture pouring it over almonds for a carob almond bark
The maple and vanilla flavor is interesting and needs further exploration. A more basic bark would just use simple syrup
Tree nuts are good for you in moderation. As a vegetarian I'm supposed to have 30 to 50 grams a day of almonds, cashews, pecans or walnuts. All great things in my book. Here's a neat little salad for pecans
Apple-Pecan Broccoli Salad
° 6 ounces broccoli slaw or one cup shredded broccoli stems, one cup shredded carrots, and one cup shredded red cabbage (I cheated and used a 6 ounce commercial bag which was on sale for $2)
° one tart apple cut into matchsticks
° a handful or so of pecan halves
° 2 tbl plain Greek yogurt (I used 2% Fage)
° 2 tsp mauonnaise
° 1 tbl honey
° 1/2 tsp sweet curry powder
° 1/2 tsp fresh black pepper
° 1 tsp rice vinegar
° toast the pecans over medium heat in a dry frying pan until you can smell them. Don't brown them!!
° In a mixing bowl whisk the dressing ingredients. Add the salad ingredients except for the pecans and toss
For the third item I note that pasteurized eggs are starting to show up in some stores. The brand around here is Safest Choice and their webpage has a store list. When you bake and are experimenting it can be very useful to sample the dough or batter and this allows you to do it safely. Refining the recipe for Sukie's carob cake was easy - I made a master batch of batter and broke it into ten parts each of which I varied something. Using two main batches I could conduct twenty trials in a few hours and was able to find a few variations that stood out from the rest. You can also make foods like eggnog, some ice creams or just snack on chocolate chip cookie dough safely and that is worth the high price every now and again.
And finally an observation. In rebalancing the temperature in our refrigerator as it started working after the massive power outage of superstorm Sandy I managed to nearly freeze a greek yogurt. Once or twice a week my breakfast features a 200g container of Fage 2% plain greek yogurt, about 14g of walnuts or cashews and some berry jam and fresh berries. The yogurt is usually refrigerator temperature - about 40°F. Near freezing - say 33° or 34°F - the yogurt becomes extra thick and smooth making the mixture even better - much better I think.
So try chilling your yogurt to get it near freezing - without managing to actually freeze the stuff.