Global Stratospheric Ozone Reduction - Air Pollution and Global Warming: History, Science, and Solutions - page 260

more readily in the troposphere than do CFCs, HCFCs
still contain chlorine, some of which can reach the
stratosphere and damage the ozone layer. Table 11.4
shows the phase-out schedule of HCFCs, as modified
by amendments through 2010 to the Montreal Protocol
Developed countries are given less time to eliminate
consumption than developing countries.
As CFC and HCFC emissions have declined, emis-
sions of HFCs have taken their place (Figure 11.20).
HFCs contain no chlorine and do not pose a known
threat to the ozone layer. Unfortunately, they are strong
absorbers of thermal-IR radiation and contribute to
global warming, as indicated by their global warming
potentials (Table 11.2). As such, efforts are also now
under way to phase out HFCs as a result of their global
warming effects.
Because CFC emissions have declined due to the
Montreal Protocol, tropospheric mixing ratios of CFC-
11 have begun to decrease and those of CFC-12 have
begun to level off (Figure 11.21a). Steady decreases in
carbon tetrachloride [CCl 4 (g)], and dramatic decreases
in methyl chloroform [CH 3 CCl 3 (g)] have also occurred
(Figure 11.21b). HCFC-22 (Figure 11.21b) and -142b
(Figure 11.21c) mixing ratios continued to increase
through 2010, as did the replacement compound, SF 6 (g)
(Figure 11.21d).

Table 11.4. Percentage of 1989 baseline
hydrochlorofluorocarbon production and
consumption allowed in developed countries under
the Montreal Protocol and its amendments by year

Percent reduction Percent reduction

in consumption in consumption

and production in in developing

Year developed countries countries

2004 30

2010 75

2013 0

2015 90

2016 10

2020 99.5 35

2025 67.5

2030 100 97.5

2040 100

Fordeveloped countries, the baseline consumption equals 2.8
percent of the 1989 chlorofluorocarbon (CFC) consumption plus
100 percent of the 1989 hydrochlorofluorocarbon (HCFC) con-
sumption by the country. For these countries, the baseline pro-
duction equals the average of (a) the 1989 HCFC production plus
2.8 percent of the 1989 CFC production and (b) the 1989 HCFC
consumption plus 2.8 percent of the 1989 CFC consumption. For
developing countries, the baseline consumption in 2013 is the
average consumption in 2009 and 2010.

700 300

CH 3 Cl

250

600

HCFC-22

CFC-12

200

500

150

CCl 4 (g)

400

100

CFC -11

300

CH 3 CCl 3 (g)

50

200

0

1990 1995 2000 2005 2010

1988 1992 1996 2000 2004 2008 2012

(a) Year (b) Year

100 10

8

80 SF 6 (g)

CFC-113

60 6

40 4

H-1211

HCFC-142b

20 2

0 0

1995 2000 2005 2010 2000 2005 2010

(c) Year

(d) Year

Figure 11.21. Change in mixing ratio of several (a, b) chlorinated gases at Mauna Loa Observatory, Hawaii,
1987-2011, (c) fluorinated gases since 1994 at Mace Head, Ireland, and (d) a halon and sulfur hexafluoride at
Mauna Loa since 1999. Data from Mauna Loa Data Center (n.d.).