Seasonal and inter-annual variability of lower stratospheric age of air spectra

Ploeger, Felix; Birner, Thomas

doi:10.5194/acp-16-10195-2016

Cited by 66 publications

(158 citation statements)

References 52 publications

(93 reference statements)

Supporting

Mentioning

132

Contrasting

Order By: Relevance

“…This suggests that the log(TGM)-ozone relationship in the lowermost stratosphere is set in part by mixing rather than solely by chemistry (Xiao et al, 2007). The model underestimate of the log(TGM)-ozone slope could reflect excessive dynamical mixing in the lower stratosphere, a well-known problem in stratospheric transport models (Schoeberl et al, 2003;Tan et al, 2004), or errors in the timescales of air transit across the tropopause, which vary on the order of months to years (Orbe et al, 2014;Ploeger and Birner, 2016).…”

Section: Vertical Distribution and The Stratospherementioning

confidence: 99%

A new mechanism for atmospheric mercury redox chemistry: implications for the global mercury budget

et al. 2017

View full text Add to dashboard Cite

Abstract. Mercury (Hg) is emitted to the atmosphere mainly as volatile elemental Hg 0 . Oxidation to water-soluble Hg II plays a major role in Hg deposition to ecosystems. Here, we implement a new mechanism for atmospheric Hg 0 / Hg II redox chemistry in the GEOS-Chem global model and examine the implications for the global atmospheric Hg budget and deposition patterns. Our simulation includes a new coupling of GEOS-Chem to an ocean general circulation model (MITgcm), enabling a global 3-D representation of atmosphereocean Hg 0 / Hg II cycling. We find that atomic bromine (Br) of marine organobromine origin is the main atmospheric Hg 0 oxidant and that second-stage HgBr oxidation is mainly by the NO 2 and HO 2 radicals. The resulting chemical lifetime of tropospheric Hg 0 against oxidation is 2.7 months, shorter than in previous models. Fast Hg II atmospheric reduction must occur in order to match the ∼ 6-month lifetime of Hg against deposition implied by the observed atmospheric variability of total gaseous mercury (TGM ≡ Hg 0 + Hg II (g)). We implement this reduction in GEOS-Chem as photolysis of aqueous-phase Hg II -organic complexes in aerosols and clouds, resulting in a TGM lifetime of 5.2 months against deposition and matching both mean observed TGM and its variability. Model sensitivity analysis shows that the interhemispheric gradient of TGM, previously used to infer a longer Hg lifetime against deposition, is misleading because Southern Hemisphere Hg mainly originates from oceanic emissions rather than transport from the Northern Hemisphere.The model reproduces the observed seasonal TGM variation at northern midlatitudes (maximum in February, minimum in September) driven by chemistry and oceanic evasion, but it does not reproduce the lack of seasonality observed at southern hemispheric marine sites. Aircraft observations in the lowermost stratosphere show a strong TGM-ozone relationship indicative of fast Hg 0 oxidation, but we show that this relationship provides only a weak test of Hg chemistry because it is also influenced by mixing. The model reproduces observed Hg wet deposition fluxes over North America, Europe, and China with little bias (0-30 %). It reproduces qualitatively the observed maximum in US deposition around the Gulf of Mexico, reflecting a combination of deep convection and availability of NO 2 and HO 2 radicals for second-stage HgBr oxidation. However, the magnitude of this maximum is underestimated. The relatively low observed Hg wet deposition over rural China is attributed to fast Hg II reduction in the presence of high organic aerosol concentrations. We find that 80 % of Hg II deposition is to the global oceans, reflecting the marine origin of Br and low concentrations of organic aerosols for Hg II reduction. Most of that deposition takes place to the tropical oceans due to the availability of HO 2 and NO 2 for second-stage HgBr oxidation.

show abstract

Section: Vertical Distribution and The Stratospherementioning

confidence: 99%

A new mechanism for atmospheric mercury redox chemistry: implications for the global mercury budget

et al. 2017

View full text Add to dashboard Cite

show abstract

“…This first moment of the arrival time distribution has a lower value than the mean age and is termed the mean arrival time. Information on the mean arrival time was derived from 2-D model calculations by Plumb et al (1999), who used the mean arrival time to detrend stratospheric correlations. They found that the detrended correlations from different years showed good agreement, if the mean arrival time was used in calculating the reference values, while this was not the case when using mean age.…”

mentioning

confidence: 99%

“…The age spectrum G used here is that for an inert tracer. As shown by Plumb et al (1999) and Ostermöller et al (2017), the arrival time distribution is better suited to describe the propagation of the organic fraction of a source gas into the stratosphere. Consequently, it is also expected that the age spectrum for an inert tracer may not be the best way to describe the propagation and release of the inorganic fraction and thus EESC.…”

mentioning

confidence: 99%

“…In addition to transport and temporal trends in the troposphere, the stratospheric mixing ratio of a species with chemical loss in the stratosphere depends on the loss processes and on the interplay between transport, chemical loss and the temporal trend (Volk et al, 1997;Plumb et al, 1999). The age spectrum G, which is used to describe the propagation of chemically inert trace gases into the stratosphere (Schauffler et al, 2003;Engel et al, 2002) and to calculate mean age, does not take into account chemical loss.…”

mentioning

confidence: 99%

See 1 more Smart Citation

A refined method for calculating equivalent effective stratospheric chlorine

et al. 2018

View full text Add to dashboard Cite

Abstract. Chlorine and bromine atoms lead to catalytic depletion of ozone in the stratosphere. Therefore the use and production of ozone-depleting substances (ODSs) containing chlorine and bromine is regulated by the Montreal Protocol to protect the ozone layer. Equivalent effective stratospheric chlorine (EESC) has been adopted as an appropriate metric to describe the combined effects of chlorine and bromine released from halocarbons on stratospheric ozone. Here we revisit the concept of calculating EESC. We derive a refined formulation of EESC based on an advanced concept of ODS propagation into the stratosphere and reactive halogen release. A new transit time distribution is introduced in which the age spectrum for an inert tracer is weighted with the release function for inorganic halogen from the source gases. This distribution is termed the "release time distribution". We show that a much better agreement with inorganic halogen loading from the chemistry transport model TOM-CAT is achieved compared with using the current formulation. The refined formulation shows EESC levels in the year 1980 for the mid-latitude lower stratosphere, which are significantly lower than previously calculated. The year 1980 is commonly used as a benchmark to which EESC must return in order to reach significant progress towards halogen and ozone recovery. Assuming that -under otherwise unchanged conditions -the EESC value must return to the same level in order for ozone to fully recover, we show that it will take more than 10 years longer than estimated in this region of the stratosphere with the current method for calculation of EESC. We also present a range of sensitivity studies to investigate the effect of changes and uncertainties in the fractional release factors and in the assumptions on the shape of the release time distributions. We further discuss the value of EESC as a proxy for future evolution of inorganic halogen loading under changing atmospheric dynamics using simulations from the EMAC model. We show that while the expected changes in stratospheric transport lead to significant differences between EESC and modelled inorganic halogen loading at constant mean age, EESC is a reasonable proxy for modelled inorganic halogen on a constant pressure level.

show abstract

“…In addition, convective uplift by typhoons has been shown to inject air masses into the outer region of the anticyclonic circulation . The interplay of these processes results in fast upward transport into the lower stratosphere and an enhanced fraction of young air in the monsoon UTLS region (Ploeger and Birner, 2016). Convection over land causes particularly fast upward transport (Tissier and Legras, 2016).…”

Section: Introductionmentioning

confidence: 99%

Quantifying pollution transport from the Asian monsoon anticyclone into the lower stratosphere

et al. 2017

Self Cite

View full text Add to dashboard Cite

Abstract. Pollution transport from the surface to the stratosphere within the Asian monsoon circulation may cause harmful effects on stratospheric chemistry and climate. Here, we investigate air mass transport from the monsoon anticyclone into the stratosphere using a Lagrangian chemistry transport model. We show how two main transport pathways from the anticyclone emerge: (i) into the tropical stratosphere (tropical pipe), and (ii) into the Northern Hemisphere (NH) extratropical lower stratosphere. Maximum anticyclone air mass fractions reach around 5 % in the tropical pipe and 15 % in the extratropical lowermost stratosphere over the course of a year. The anticyclone air mass fraction correlates well with satellite hydrogen cyanide (HCN) and carbon monoxide (CO) observations, confirming that pollution is transported deep into the tropical stratosphere from the Asian monsoon anticyclone. Cross-tropopause transport occurs in a vertical chimney, but with the pollutants transported quasihorizontally along isentropes above the tropopause into the tropics and NH.

show abstract

Seasonal and inter-annual variability of lower stratospheric age of air spectra

Cited by 66 publications

References 52 publications

A new mechanism for atmospheric mercury redox chemistry: implications for the global mercury budget

A new mechanism for atmospheric mercury redox chemistry: implications for the global mercury budget

A refined method for calculating equivalent effective stratospheric chlorine

Quantifying pollution transport from the Asian monsoon anticyclone into the lower stratosphere

Contact Info

Product

Resources

About