Page 41 - Read Online

Page 6 of 13 Cheng et al. Carbon Footprints 2024;3:10 https://dx.doi.org/10.20517/cf.2023.53

where f (x,t ) represents the mass of gas i remaining in the atmosphere after t years (Eqs. 6 and 7). RE i
i
E
-1
-2
represents the radiative efficiency (W m kg ), i.e., the instantaneous radiative forcing to the earth’s surface
per unit mass of greenhouse gas I, which can be expressed as the times of the CO reference gas .
[25]
2
Supplementary Table 7 gives details.
The exponential decay function of CH and N O is as follows:
4
2

where represents the lifetime of GHG i in the atmosphere (year; CH and N O with a lifetime of 12.4 and
i
2
4
121 years, respectively).
For CO , the decay function of CO is as follows:
2
2

where parameters of a = 0.2173, a = 0.2240, a = 0.2824, a = 0.2763, = 394.4, = 36.54, = 4.304 of
3
0
1
2
3
2
1
IPCC AR5 were used, in addition to the parameters of 16 CO impulse-response functions summarized by
2
Joos et al. (2013). Supplementary Table 8 gives details .
[26]
Referring to Eqs. 4-7, the TRF of the three greenhouse gases of CO , CH , and N O were derived as Eqs. 8-
2
4
2
10.

RESULTS
Comparison of climate performance at the baseline
Figure 2 shows the GWP of fresh lettuce cultivated by traditional sunlight greenhouse and by plant factory.
In the baseline of China Southern Power Grid, the 100-year GWP of 1 kg of lettuce produced in the plant
factory is over 50 times higher than that of cultivated in the greenhouse. The methane (nitrous oxide)
emissions contribute 9(14)% to the GWP of greenhouse and 16(1)% to plant factory [Figure 2A]. The
application of nitrogen fertilizers (70%-75%) and polyethylene film (10%-14%) are the two main sources of
GWP for greenhouse; while power consumption (43%-99%, Figure 2B) is the largest contributor to the
GWP of plant factory. The climate performance of the plant factory varies with power sources. For example,
the 100-year GWP of plant factory powered by fossil fuels (13-25 kgCO e in P , which represent plant
2
1-3
factory that uses coal, oil, and natural gas to generate electricity, respectively) is substantially higher than