Hello, I know that Scientist do not consider human respiration for calculating CO2 concentration becuase CO2 from the human are from the food. However, when we consider CO2 flux, we cannot ignore the human breath. I want to compare human CO2 emission factor with cars. So, my question is "If people walk 1 km. How much of CO2 will be emitted?".
Thanks
Hi
Follow the link
https://www.carboncommentary.com/blog/2014/07/22/walking-can-be-more-carbon-intensive-than-driving
https://www.globe.gov/explore-science/scientists-blog/archived-posts/sciblog/index.html_p=186.html
https://www.google.co.in/amp/s/micpohling.wordpress.com/2007/03/27/math-how-much-co2-is-emitted-by-human-on-earth-annually/amp/
Recommend answer if useful.
According to this Quora answer (validity check required) https://www.quora.com/What-is-the-mass-of-the-carbon-dioxide-exhaled-in-a-breath
a healthy adult inhales/exhales 7ml/kg of his/her body mass - about 500ml/kg in tidal wave
In exhale, about 4% is CO2
Plug in 75kg (average weight of an adult), we have 36.84mg of CO2/breathe, with ~70 breath/minute, it is 2578.8mg, or 2.57g/minute
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For a car, it is estimated 4.6 tons of CO2 per year. So, assume the car is used everyday, with total usage of 4 hour/day, we have 3.15kg/day, further divide this number yields 2.19g/minute.
Source: https://www.epa.gov/greenvehicles/greenhouse-gas-emissions-typical-passenger-vehicle
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Check the other answer to see if it is also useful - my class just resumes after the break, and my teacher is a bit strict on using laptop in class.
Hoang,
The tidal breath is about half a litre (not per kg, half a litre per person).
The mean concentration in the exhale is ~5%.
So that's ~25ml per breath for one person.
One exhales 15 times a minutes.
So in one minute one generates 375ml of CO2.
(1 mole of CO2 weighs 44 grammes, and has a volume of 24 litres)
So we know that 0.38 litres is the volume of 0.7 grammes of CO2.
That's one minute of respiration.
Go from there. Perhaps the person walks that 1km in 20 min.
They might do so with a raised metabolic rate.
So a 1km stroll may generate ~15 grammes of CO2.
Thanks @James Garry for his comment - I'm not even sure about how to calculate the exhale of CO2 for each person, his comment surely helps!
The energy released or CO2 released depends on walking speed. I give following estimates at rest and when walking at speed of 5 km/h.
REST: The heating value per kg of O2 consumed is approximately constant for most fuels and nutrients { glucose, fat } at 14000 J/g of O2 consumed or 448000 J/mole of O2 consumed . Then one can show that [http://downloads.hindawi.com/journals/jc/2018/1270708.pdf]
CO2 in g/MJ or CO2 in kg/GJ = 100 RQ, { 100 is number rounded from 98.2)
Where RQ= CO2 moles/O2 moles consumed in oxidation process . Oxidation of C6H12O6 (glucose) consume 6 O2 moles and produces 6 CO2 and 6 H2O moles. Hence RQ=1 and for fat , RQ=0.7. The metabolic rate of 70 kg Human is about 80 Watts ( at rest) and hence energy released per min is 4.8 kJ 0r 0.0048 MJ and RQ for glucose =1. hence CO2 in g= 100*1*0.0048= 0.48 g per mi or { 0.48/70} =0.0069 g/min per kg body mass or 0.0069( g/min per kg body mass *1000 (mL/L/1.96 (g/L) =3.50 mL/min per kg body mass since density of CO2 = 1.96 g/L. {CST}.
If no of breathes /min=15, then CO2 in mg per breath is = 0.48*1000/15=32 mg/breathe which checks with typical values of 34 mg per breathe.
Walking at 5 km/h: Met. Rate is 280 Watts [https://courses.lumenlearning.com/physics/chapter/7-8-work-energy-and-power-in-humans/] and hence CO2 emitted will be (280/80)*0.48 =1.68 g of CO2 per min .
The average human exhales about 2.3 pounds of carbon dioxide on an average day. (The exact quantity depends on your activity level—a person engaged in vigorous exercise produces up to eight times as much CO2 as his sedentary brethren.) Take this number and multiply by a population of 7 billion people, breathing away for 365.25 days per year, and you get an annual CO2 output of 2.94 billion tons. International carbon dioxide emissions from fossil-fuel combustion for 2008 topped 34.7 billion tons. So the human race breathes out about 8.5 percent as much carbon as we burn.
Reference: https://www.nrdc.org/onearth/waiting-exhale
Best regards.
Annual CO2 in tons per year per person: The energy released per kg of O2 consumed is approximately constant for most fuels and nutrients {glucose, fat} at 14000 J/g of O2 consumed or 448000 J/mole of O2 consumed. Then one can show that [http://downloads.hindawi.com/journals/jc/2018/1270708.pdf (https://www.researchgate.net/deref/http%3A%2F%2Fdownloads.hindawi.com%2Fjournals%2Fjc%2F2018%2F1270708.pdf)]
CO2 in g/MJ or CO2 in kg/GJ = 100 RQ, CO2 in tons/GJ = 0.1*RQ,
Where RQ= CO2 moles/O2 moles consumed in oxidation process. Oxidation of C6H12O6 (glucose) consume 6 O2 moles and produces 6 CO2 and 6 H2O moles. Hence RQ=1 and for fat, RQ=0.7. For typical humans, RQ= 0.84 since both fat and CH are oxidized.70 kg person releases 80 W , daily release 6912 kJ, annually releases 2.5 GJ. Thus with RQ=0.84, CO2 in tons per year per person=0.1*2.5*0.84=0.21 Tons per year per person
With 7 billion population, CO2 emission per year = 1.5 billion tons/year
As obesity increases energy consumption increases or when people consume more carbohydrate ( RQ=1) annual emission increases.
LIFETIME CO2 in Tons per person: According to Rubner’s hypothesis, energy released over lifetime (LTER) ranges from 590-1100 MJ/kg body mass [Speakman, J.R. J. Exp. Biol. 2005, 208, 1717]. If LTER=850 MJ/kg body mass, then with RQ= 0.84, CO2 in kg per kg body mass over lifetime= 850 MJ/kg body mass* {100*0.84 g of CO2 per MJ}/1000 g per kg = 71.4 kg of CO2 per kg body mass. Assuming body mass to be 70 kg, lifetime CO2 emission is 71.4*70/1000= 5 tons per human. As obesity increases annual emission increases but life time emission may not increase since life span is reduced.