(CALIPSO, SAGE-II), balloonsonde, and the CAREBIC
aircraft reveal that the ATAL is composed of nitrates, sulfate, BC, organic aerosols, and dust particles (Vernier et al.
2018). Studies indicate that these aerosols are transported
into the lower stratosphere and produce a significant impact
on stratospheric temperature and circulations (Fadnavis et al.
2017). MERRA-2 data also shows abundant quantities of
carbonaceous aerosols and dust in the mid and upper troposphere over India, arising from enhanced biomass burning
emissions as well as westerly transport from the Middle East
deserts during May–June (Lau et al. 2018). Model simulations indicate that carbonaceous aerosol transport into the
UTLS enhances heating rates by *0.03–0.08 K per day in
the upper troposphere (300–100 hPa). These carbonaceous
aerosols induce a seasonal mean anomaly aerosol radiative
forcing of *+ 0.37 ± 0.26 W m
−2 at the TOA and
−4.74 ± 1.42 W m
−2 at the surface (Fadnavis et al. 2017).
Asian summer monsoon anticyclone region contributes an
increase of *15% to the Northern Hemisphere column
stratospheric aerosol. This elevated aerosol layer also aids in
aggravating monsoon droughts during an El Niño episode
(Fadnavis et al. 2019).
5.3 Trace Gases
Ozone variations in the troposphere and stratosphere play a
key role in maintaining the Earth’s radiative budget and
climate change (Logan et al. 2012); it is important to know
its assessment. In this section, we provide an assessment of
its trends from past literature. Trend estimates in total ozone
column, tropospheric ozone column, and surface measurements are reported from in situ observations, satellites
remote sensing, and model simulations.
5.3.1 Trends in Ozone
5.3.1.1 Total Ozone Column
The past studies report estimates of trends in the total ozone
column at various stations widespread over the Indian
region. Although, there are limited ozone monitoring stations over India, trend estimates from ground-based measurements like Dobson spectrophotometer (DU year
−1 ) and
satellite remote sensing (% year
−1 ) are consistent. Measurements over north India (20–35° N) show statistically
significant (r uncertainty level) negative (declining) trends
while they are positive (increasing) over south India (8–
20° N). For example, Multi-Sensor Reanalysis (MSR/
MSR-2) and TOMS observations over north India show a
decreasing trend of −0.08 to −0.15% year
−1 during 1979–
2008 (Tandon and Attri 2011) and −0.03 to −0.11% year
−1
during January 1979–December 2012 (Sahu et al. 2014).
The observations in south India show a positive trend of
0.01–0.03% year
−1 during January 1979–December 2012.
Dobson spectro-photometer tropospheric column ozone
measurements also show a decreasing trend −0.01 DU
year
−1 at Varanasi, (in north India), and positive trend +0.14
DU year
−1 at Kodaikanal, (in south India) during 1957 and
2015 (Pathakoti et al. 2018). The above studies indicate that
amplitude of trend varies with location and time period of
measurement, and the trend estimates have medium
confidence.
In the global context, the ozone assessment report shows
that total ozone has been stable since about 1996 in response
to emission control of ozone-depleting substances (ODSs)
(Chehade et al. 2014; Zvyagintsev et al. 2015). Future trends
in total column ozone over the globe and tropics
(25° S–25° N) are tabulated in Table 5.1 (Cionni et al. 2011;
Eyring et al. 2013).
Table 5.1 Ozone trend over the Indian region and CMIP5 annual mean future trends over tropics
Ozone
trends
Indian region
Tropics 25° S–25° N from CMIP5 annual mean future trends
(2090s–2010s) in the RCPs (Cionni et al. 2011)
Total
column
ozone
North India: − 0.03 to −0.11% year
−1
South India: +0.01 to +0.03% year
−1 (1979–2012)
(Sahu et al. 2017)
RCP 2.6: −2 DU (−1%)
RCP 4.5: 0 DU (0%)
RCP 6.0: 0 DU (0%)
RCP 8.5: 7 DU (4%)
Troposphere
Tropospheric column: 0.3 ± 2.6 to
2.7 ± 2.3%, year
−1 (Saraf and Beig 2004)
RCP 2.6: −4 DU (−17%)
RCP 4.5: −2DU (−10%)
RCP 6.0: −2DU (−10%)
RCP 8.5: +5 DU (18%)
Stratosphere
0.27 ± 0.67 to 1.3 ± 0.65% year
−1 (*200–50 mb)
(1993–2005)
−0.45 ± 0.8 to −0.57 ± 0.62% year
−1 (30–10 mb)
(1993–2005) (Fadnavis et al. 2014a)
RCP 2.6: 2 DU (1%)
RCP 4.5: 2DU (1%)
RCP 6.0: 2DU (1%)
RCP 8.5: 2DU (1%)
104
S. Fadnavis et al.
aircraft reveal that the ATAL is composed of nitrates, sulfate, BC, organic aerosols, and dust particles (Vernier et al.
2018). Studies indicate that these aerosols are transported
into the lower stratosphere and produce a significant impact
on stratospheric temperature and circulations (Fadnavis et al.
2017). MERRA-2 data also shows abundant quantities of
carbonaceous aerosols and dust in the mid and upper troposphere over India, arising from enhanced biomass burning
emissions as well as westerly transport from the Middle East
deserts during May–June (Lau et al. 2018). Model simulations indicate that carbonaceous aerosol transport into the
UTLS enhances heating rates by *0.03–0.08 K per day in
the upper troposphere (300–100 hPa). These carbonaceous
aerosols induce a seasonal mean anomaly aerosol radiative
forcing of *+ 0.37 ± 0.26 W m
−2 at the TOA and
−4.74 ± 1.42 W m
−2 at the surface (Fadnavis et al. 2017).
Asian summer monsoon anticyclone region contributes an
increase of *15% to the Northern Hemisphere column
stratospheric aerosol. This elevated aerosol layer also aids in
aggravating monsoon droughts during an El Niño episode
(Fadnavis et al. 2019).
5.3 Trace Gases
Ozone variations in the troposphere and stratosphere play a
key role in maintaining the Earth’s radiative budget and
climate change (Logan et al. 2012); it is important to know
its assessment. In this section, we provide an assessment of
its trends from past literature. Trend estimates in total ozone
column, tropospheric ozone column, and surface measurements are reported from in situ observations, satellites
remote sensing, and model simulations.
5.3.1 Trends in Ozone
5.3.1.1 Total Ozone Column
The past studies report estimates of trends in the total ozone
column at various stations widespread over the Indian
region. Although, there are limited ozone monitoring stations over India, trend estimates from ground-based measurements like Dobson spectrophotometer (DU year
−1 ) and
satellite remote sensing (% year
−1 ) are consistent. Measurements over north India (20–35° N) show statistically
significant (r uncertainty level) negative (declining) trends
while they are positive (increasing) over south India (8–
20° N). For example, Multi-Sensor Reanalysis (MSR/
MSR-2) and TOMS observations over north India show a
decreasing trend of −0.08 to −0.15% year
−1 during 1979–
2008 (Tandon and Attri 2011) and −0.03 to −0.11% year
−1
during January 1979–December 2012 (Sahu et al. 2014).
The observations in south India show a positive trend of
0.01–0.03% year
−1 during January 1979–December 2012.
Dobson spectro-photometer tropospheric column ozone
measurements also show a decreasing trend −0.01 DU
year
−1 at Varanasi, (in north India), and positive trend +0.14
DU year
−1 at Kodaikanal, (in south India) during 1957 and
2015 (Pathakoti et al. 2018). The above studies indicate that
amplitude of trend varies with location and time period of
measurement, and the trend estimates have medium
confidence.
In the global context, the ozone assessment report shows
that total ozone has been stable since about 1996 in response
to emission control of ozone-depleting substances (ODSs)
(Chehade et al. 2014; Zvyagintsev et al. 2015). Future trends
in total column ozone over the globe and tropics
(25° S–25° N) are tabulated in Table 5.1 (Cionni et al. 2011;
Eyring et al. 2013).
Table 5.1 Ozone trend over the Indian region and CMIP5 annual mean future trends over tropics
Ozone
trends
Indian region
Tropics 25° S–25° N from CMIP5 annual mean future trends
(2090s–2010s) in the RCPs (Cionni et al. 2011)
Total
column
ozone
North India: − 0.03 to −0.11% year
−1
South India: +0.01 to +0.03% year
−1 (1979–2012)
(Sahu et al. 2017)
RCP 2.6: −2 DU (−1%)
RCP 4.5: 0 DU (0%)
RCP 6.0: 0 DU (0%)
RCP 8.5: 7 DU (4%)
Troposphere
Tropospheric column: 0.3 ± 2.6 to
2.7 ± 2.3%, year
−1 (Saraf and Beig 2004)
RCP 2.6: −4 DU (−17%)
RCP 4.5: −2DU (−10%)
RCP 6.0: −2DU (−10%)
RCP 8.5: +5 DU (18%)
Stratosphere
0.27 ± 0.67 to 1.3 ± 0.65% year
−1 (*200–50 mb)
(1993–2005)
−0.45 ± 0.8 to −0.57 ± 0.62% year
−1 (30–10 mb)
(1993–2005) (Fadnavis et al. 2014a)
RCP 2.6: 2 DU (1%)
RCP 4.5: 2DU (1%)
RCP 6.0: 2DU (1%)
RCP 8.5: 2DU (1%)
104
S. Fadnavis et al.