Observations have shown that the global mass of nitrogen dioxide decreased in both hemispheres in the year following the eruption of Mt. Pinatubo. In contrast, the observed ozone response was largely asymmetrical with respect to the equator, with a decrease in the northern hemisphere and little change and even a small increase in the southern hemisphere. Simulations including enhanced heterogeneous chemistry due to the presence of the volcanic aerosol reproduce a decrease of ozone in the northern hemisphere, but also produce a comparable ozone decrease in the southern hemisphere, contrary to observations. Our simulations show that the heating due to the volcanic aerosol enhanced both the tropical upwelling and the extratropical downwelling. The enhanced extratropical downwelling, combined with the time of the eruption relative to the phase of the Brewer-Dobson circulation, increased the ozone in the southern hemisphere and counteracted the ozone depletion due to heterogeneous chemistry on volcanic aerosol

Aquila, Valentina

Douglass, A. R.

Newman, P. A.

Oman, Luke D.

Stolarski, R.

NASA Technical Reports Server

1 The response of ozone and nitrogen dioxide to the eruption of Mt. Pinatubo. 
2 V. Aquila, L. D. Oman, R. Stolarski, A. R. Douglass, P. A. Newman 
3 
4 Abstract 
5 Observations have shown that the global mass of nitrogen dioxide decreased in both 
6 hemispheres in the year following the eruption of Mt. Pinatubo. In contrast, the observed 
7 ozone response was largely asymmetrical with respect to the equator, with a decrease in 
8 the northern hemisphere and little change and even a small increase in the southern 
9 hemisphere. Simulations including enhanced heterogeneous chemistry due to the presence 
10 of the volcanic aerosol reproduce a decrease of ozone in the northern hemisphere, but also 
11 produce a comparable ozone decrease in the southern hemisphere, contrary to 
12 observations. Our simulations show that the heating due to the volcanic aerosol enhanced 
13 both the tropical upwelling and the extratropical downwelling. The enhanced extratropical 
14 downwelling, combined with the time of the eruption relative to the phase of the Brewer-
15 Dobson circulation, increased the ozone in the southern hemisphere and counteracted the 
16 ozone depletion due to heterogeneous chemistry on volcanic aerosol. 
https://ntrs.nasa.gov/search.jsp?R=20120013293 2019-08-30T21:38:17+00:00Z
23 magnitude over background. This perturbation persisted in the atmosphere for several 
24 years. 
25 Aerosol from Mt. Pinatubo changed both the stratospheric chemistry and 
26 dynamics. The volcanic sulfate provided additional surface for heterogeneous chemistry, 
27 impacting especially the concentrations of ozone and nitrogen dioxide (N02) [Tie and 
28 Brasseur, 1995]. Heating by this volcanic aerosol also changed the radiative balance of the 
29 atmosphere, intensifying upwelling in the tropics and downwelling in the extra-tropics 
30 [e.g. Pitari and Mancini, 2002; Aquila et aI., 2012]. 
31 Observations showed depletion of stratospheric N02 in both hemispheres during 
32 the years following the eruption [Johnston et aI., 1992, Van Roozendael et al., 1997]. The 
33 observed ozone response to the volcanic perturbation, on the other hand, was different in 
34 the northern (NH) and in the southern hemisphere (SH). While column ozone generally 
35 decreased in the NH, an increase of the ozone column was detected at southern mid- and 
36 high latitudes during the year following the eruption [Randel and Wu, 1996]. Several 
37 model studies attribute the observed NH depletion to the enhancement of heterogeneous 
38 chemistry because of the volcanic aerosols [e.g. Tie and Brasseur, 1995]. 
39 The volcanic impact on the stratospheric chemistry cannot explain the asymmetric 
40 ozone perturbation observed in the NH and SH [Stolarski et aI., 2006], and several studies 
41 suggested explanations other than a chemistry perturbation. Randel and Wu [1996] 
42 showed that the quasi-biannual oscillation (QBO) increased ozone in the extratropical SH 
during 1 992 is not large to explain the observed 
et ozone 
an 
46 ozone depletion to interannual dynamical variability, which masked the Pinatubo aerosol 
47 chemical effect in the SH. However, these studies cannot distinguish between natural 
48 interannual variability and circulation changes forced by the volcanic perturbation. 
49 Poberaj et al. [2011] performed a multiple linear regression analysis to the Chemical and 
50 Dynamical Influences on Decadal Ozone Change (CANDIDOZ), stating that volcanically 
51 induced chemical ozone depletion was overcompensated by the QBO and by a 
52 pronounced EP flux anomaly. 
53 Here, using a free-running global chemistry climate model (Section 2), we separate 
54 the photochemical and dynamical contributions to the ozone and N02 anomalies induced 
55 by the volcanic perturbation (Section 3). Section 4 presents the main conclusions of this 
56 work. 
57 2. Model and simulation 
58 All simulations are performed with the Goddard Earth Observing System, Version 
59 5 (GEOS-S) model [Rienecker et al., 2008], a system of component models integrated 
60 using the Earth System Modeling Framework (ESMF). For these simulations GEOS-S is 
61 coupled to the GOCART aerosol transport module [Calarco et aI., 2010] and a 
62 stratospheric chemistry module [Pawson et ai., 2008]. The resolution is 2.00 x 2.So 
63 latitude by longitude with 72 vertical layers from surface to 0.01 hPa 95 km). This 
64 version of GEOS-5 does not simulate the QBO. The model is forced with observed sea 
65 surface temperatures and sea ice concentrations [Reynolds et aI., 2002]. Aquila et al. 
[2012] a more detailed description model and an evaluation the 
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GOCART computes the transformation of S02 into sulfate aerosol. The 
simulations shown here use prescribed aerosol surface area density for heterogeneous 
chemistry from SAM II, SAGE and SAGE-II data [Eyring et al .. 2008]. GEOS-5 also 
includes an option for calculating the aerosol surface area density online using the mass of 
sulfate aerosol and relative humidity. 
We simulate the eruption of Mt. Pinatubo by injecting 20 Tg of S02 between 16 
km and 18 km in the volcano's model grid box on 15 June 1991. No other aerosol sources 
are included in the simulation. We performed four model experiments (Table 1), each 
composed of 10 simulations with different sets of initial conditions typical of the year 
2000. The results shown here are ensemble averages. 
The first experiment (experiment REF) is a control ensemble that does not include 
any volcanic perturbation. 
The second experiment (experiment DYN) includes radiatively interactive aerosol. 
This experiment uses for heterogeneous chemistry prescribed aerosol surface area density 
from SAM II and SAGE observations relative to 1979, when the stratospheric aerosol 
layer is considered to be in an unperturbed condition [Thomason et aI., 1997]. Hence, this 
experiment includes only the volcanic perturbation to the stratospheric dynamics. 
The third experiment (experiment CHEM) does not include radiatively interactive 
aerosol, and uses aerosol surface area density from SAGE-II data appropriate for the 
simulated year. In this experiment the aerosol cannot modify the simulated meteorology, 
there is a VUeHYU to stratospheric V.'''...,'Uh.> no perturbation to 
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The fourth experiment (experiment FULL) includes radiatively interactive aerosols 
and the aerosol surface area density for the simulated year. This experiment includes the 
volcanic perturbation to both the dynamics and the stratospheric chemistry. 
3. Results 
The comparison of the experiment FULL with the control experiment REF 
identifies the complete perturbation of ozone and N02 due to Mt. Pinatubo. The 
comparisons of experiments DYN and CHEM with experiment REF isolate the anomalies 
of ozone and N02 due to the eruption effect on the atmospheric dynamics and 
heterogeneous chemistry, respectively. 
The left panel of Fig. 1 shows observed deviations of stratospheric N02 column 
(black line) over Lauder, New Zealand with a Visible and Ultraviolet (UV/Vis) 
spectrophotometer (Johnston and A1cKenzie, 1984) from the observed monthly means 
over the years 1997 to 2003. In the same panel we also show the simulated anomalies of 
the stratospheric zonal mean N02 column, calculated as the difference between 
experiment REF from the experiments FULL (red line), CHEM (blue line), and DYN 
(green line), respectively. While the experiment including only the perturbation to the 
dynamics does not show any significant perturbation of N02, both experiments CHEM 
and FULL present a decrease of stratospheric N02, as in the observations. This shows that 
the perturbation ofN02 is dominated by the volcanic effect on the stratospheric chemistry, 
which is similar in both hemispheres (Fig. 1, right panel). 
Experiments performed using online calculation the aerosol surface area 
a 
113 higher surface area than that derived from the observations. Due to the sparse sampling, 
114 SAGE-II might have underestimated the transport rate of the aerosol from the tropics to 
115 midlatitudes. 
116 The ozone concentration responds differently to the inclusion of the volcanic 
117 perturbation to the dynamics. The left panel of Fig. 2 compares the anomalies of the total 
118 ozone column, zonally averaged between 300 S and 60 o S, as calculated from Total Ozone 
119 Mapping Spectrometer (TOMS) data (Herman et al .. 1996, AkPeters et ai., 1996) and as 
120 simulated by GEOS-5. The observed anomalies (black line) are calculated as the deviation 
121 from the 1987-1990 monthly means after eliminating the depletion due to increasing 
122 chlorine. The data show a positive anomaly for one year after the eruption, simulated also 
123 in the experiments DYN and FULL. This positive anomaly is induced by the absorption of 
124 largely longwave radiation by the volcanic aerosol, which leads to an increase in the 
125 Brewer-Dobson circulation (Aquila et ai., 2012) and to a subsequent positive anomaly of 
126 ozone total column in the southern hemisphere (Fig.2, right panel). The experiment DYN 
127 does not produce any significant perturbation after the initial positive anomaly, while the 
128 experiment CHEM shows a significant negative perturbation starting from April 1992. 
129 The ozone anomaly in the experiment FULL is essentially the sum of the DYN and 
130 CHEM anomalies, but the dynamical positive anomaly has delayed the negative anomaly 
131 from April to August 1992. 
132 Fig. 3 shows the simulated vertical distribution of the zonal mean ozone anomaly 
(JJA) 1991 (left panel) and September-October-November (SON) 
to to 
1 
136 we depict with the streamlines of the residual circulation anomaly. The increased tropical 
137 upwelling lifts air with lower ozone concentration, creating a negative equatorial anomaly 
138 centered at 20 hPa (Fig. 3, right panel). At the same time, the increased upwelling drives 
139 greater downwelling south of the equator, creating the positive ozone anomaly in the SH. 
140 This positive anomaly is located in the SH because of the phase of the Brewer-Dobson 
141 circulation at the time of the eruption, which is directed towards the winter hemisphere. 
142 We performed an experiment initiating a Pinatubo-like eruption on 15 January 1991 (as 
143 described in Aquila et at., 2012). There the positive ozone anomaly appeared in the NH 
144 (not shown), compatible with the different phase of the Brewer Dobson circulation. 
145 In SON 1992 (Fig. 3, right panel) the simulated ozone anomaly is mainly due to 
146 the perturbation to the chemistry. The ozone concentration is increased in the middle 
147 stratosphere due to the suppression of the NOx cycle induced by the volcanic aerosol, and 
148 decreased in the lower stratosphere due to the enhancement of the HOx and CIOx cycles. 
149 Tie and Brasseur, [1995], described this chemical response to the volcanic aerosoL 
150 4. Conclusions 
151 The lack of observed ozone depletion due to the eruption of Mt. Pinatubo in the 
152 southern hemisphere, contrary to the clear depletion of N02, has been an outstanding 
153 puzzle for many years [Wl\10, 2011]. We have shown that the perturbation of the 
154 stratospheric dynamics by the Mt. Pinatubo eruption is responsible for the lack of an 
155 observed ozone decrease in the SH. The dynamics response to the volcanic perturbation 
dominates ozone column during 6 months after eruption and 
1 
1 one to 
159 chemistry and to the dynamics have an additive effect, resulting in the lack of ozone 
160 depletion in the year following the eruption. 
161 On the other hand, the N02 anomaly is completely driven by the chemistry 
162 perturbation and is insensitive to the dynamics perturbation. The reason is the much 
163 shorter timescale of the heterogeneous chemistry for depleting N02 compared to the 
164 timescale for depleting ozone, together with the weak N02 vertical gradient, such that 
165 changes of vertical advection do not induce large perturbations. 
166 References 
167 Aquila, V., L. D. Oman, R. S. Stolarski, P. R. Colarco, and P. A. Newman, 
168 Dispersion of the volcanic sulfate cloud from a Mount Pinatubo-like eruption, J Geophys. 
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177 Colarco, P., A. Da Silva, M. Chin, and T. Diehl (2010), Online simulations of 
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1 Stolarski, R. Douglass, Newman, J. 
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223 Thomason,., R., & 997). comparison 
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236 
237 Table 1: list of performed experiments. 
Experiment Radiatively Year for sulfate Perturbation to 
I 
Perturbation to 
interactive aerosol area density the chemistry the dynamics 
REF No 1979 
CHEM No 1991-1995 X 
DYN Yes 1979 X 
FULL Yes 1991-1995 X X 
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239 
239 
240 Fig. 1: N02 stratospheric column anomaly versus time. Left panel: The black line marks 
241 the observed anomalies over Lauder, the red, blue and green lines show the simulated 
242 zonal mean anomaly at 4YS. The shaded areas show the standard deviation of each 
243 ensemble. Right panel: Zonal mean of the simulated N02 column anomalies in experiment 
244 FULL with respect to experiment REF. The solid lines (left) and bright areas (right) are 
245 significant at I-a level. 
246 
N02 stratospheric column - Lauder 
JMSJMSJMSJMS 
1991 1992 1993 1994 
_._. TOMS 
., , , GEOSS-FULl 
GEOSS-CHEM 
$ GEOSS-DYN 
60N 
40N 
20N 
EQ 
205 
405 
605 
N02 stratospheric column - zonal mean 
JMSJMSJMSJMS 
1991 1992 1993 1994 
-30-24-18-12 -6 0 6 12 18 24 30 
[%] 
247 Fig.2:: Ozone total column anomaly versus time. Left panel: zonal mean between 300 S 
248 and 600 S as observed by TOMS (black line) and as simulated by GEOS-5 (blue, red and 
249 green lines). The shaded areas show the standard deviation of each ensemble. Right panel: 
250 Zonal mean of the simulated ozone column anomalies in experiment FULL with respect to 
251 experiment REF. The solid lines (left) and bright areas (right) are significant at 1-0 level. 
252 
253 
Ozone total column - 30°5 to 60°5 
6 
4 
2 
~O v*.f 0 ....... 
-2 
, 
-4 
-6~~~~~~~~~~~~~~ 
JMSJMSJMSJMS 
1991 1992 1993 1994 
_._. TOMS 
" ",' GEOS5-FULL 
GEOS5-CHEM 
. GEOS5-DYN 
Ozone total column - zonal mean 
60N 
40N 
20N 
EQ 
20S 
40S 
60S J M S J M S J M S J M S 
1991 1992 1993 1994 
-1 0 -8 -6 -4 -2 0 2 4 6 8 1 0 
[%] 
254 Fig. 3: Vertical distribution of the zonal mean ozone anomaly in June-July-August 1991 
255 (left panel) and September-October-November 1992 (right panel) of the experiment FULL 
256 with respect to the experiment REF. The streamlines show the anomaly of the residual 
257 circulation. 
258 
259 
40 i. 
: 
.... 32 
.c 
en 
'(ij 
::I: 
24 
June, July, August 1991 September, October, November 1992 
-60 -40 -20 0 20 40 60 
Latitude 
1 
to 
0.. 
.c 
10 -a; 
... 
:::::s 
VI 
VI (I) 
... 
0.. 
100 


The Response of Ozone and Nitrogen Dioxide to the Eruption of Mt. Pinatubo

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