Detection of deep stratospheric intrusions by cosmogenic ³⁵ S

Abstract

The extent to which stratospheric intrusions on synoptic scales influence the tropospheric ozone (O 3 ) levels remains poorly understood, because quantitative detection of stratospheric air has been challenging. Cosmogenic 35 S mainly produced in the stratosphere has the potential to identify stratospheric air masses at ground level, but this approach has not yet been unambiguously shown. Here, we report unusually high 35 S concentrations (7,390 atoms m −3; ∼16 times greater than annual average) in fine sulfate aerosols (aerodynamic diameter less than 0.95 μm) collected at a coastal site in southern California on May 3, 2014, when groundlevel O 3 mixing ratios at air quality monitoring stations across southern California (43 of 85) exceeded the recently revised US National Ambient Air Quality Standard (daily maximum 8-h average: 70 parts per billion by volume). The stratospheric origin of the significantly enhanced 35 S level is supported by in situ measurements of air pollutants and meteorological variables, satellite observations, meteorological analysis, and box model calculations. The deep stratospheric intrusion event was driven by the coupling between midlatitude cyclones and Santa Ana winds, and it was responsible for the regional O 3 pollution episode. These results provide direct field-based evidence that 35 S is an additional sensitive and unambiguous tracer in detecting stratospheric air in the boundary layer and offer the potential for resolving the stratospheric influences on the tropospheric O 3 level.stratosphere-troposphere exchange | surface ozone | National Ambient Air Quality Standard | radioactive isotope of sulfur | Santa Ana wind H igh ground-level ozone (O 3 ) mixing ratios exert adverse impacts on human health, vegetation, and materials (1, 2). In the free troposphere, O 3 is an important greenhouse gas contributing to global warming. It also controls the lifetime of other reactive greenhouse gases through oxidation processes (3), serves as the dominant precursor of the hydroxyl radical, and enhances the oxidizing capacity of the troposphere (4). Tropospheric O 3 formation involves a series of photochemical reactions related to anthropogenic emissions of O 3 precursors [e.g., nitrogen oxides (NO x ), carbon monoxide (CO), and volatile organic compounds (VOCs)], biomass burning, and lightning (5). In addition, elevated levels of tropospheric O 3 may be caused by the intrusion of O 3 -rich stratospheric air masses (4, 6-8). Detection of such stratospheric intrusion events by field-based measurements has been a major scientific concern since the 1970s (9). Concurrent measurement of ground-level O 3 , CO, and humidity is the most common method (10, 11), but it is ambiguous and only useful in extreme events and background sites. Ozonesondes, lidar, and aircraft measurements provide high-resolution information on vertical O 3 distributions (12-14), but they are relatively expensive and not widely available. Therefore, it is crucial to find an additional and unambiguous stratospheric tracer at g...

Use of Isotope Effects To Understand the Present and Past of the Atmosphere and Climate and Track the Origin of Life

“…The 35 S nuclide is ac osmogenic isotope predominately produced in the stratosphere via the spallation of argon by cosmic rays. [179] By measuring all five sulfur isotopes ( 32 S, 33 S, 34 S, 35 S, and 36 S) in the same sulfate aerosols, Lin et al [176] found that D 33 Sv alues correlated with concentrations of stratospherically-sourced 35 S, while D 36 Sanomalies Figure 7. [179] By measuring all five sulfur isotopes ( 32 S, 33 S, 34 S, 35 S, and 36 S) in the same sulfate aerosols, Lin et al [176] found that D 33 Sv alues correlated with concentrations of stratospherically-sourced 35 S, while D 36 Sanomalies Figure 7.…”

“…Using as tate-of-the-art analytical technique (originally developed by Brothers et al [177] and further improved by Lin and Thiemens [178] ), cosmogenic 35 Sinaerosol samples can be measured in ah igh precision way and is demonstrated to be asensitive chemical tracer for identification of air masses originating from high altitudes. [179] By measuring all five sulfur isotopes ( 32 S, 33 S, 34 S, 35 S, and 36 S) in the same sulfate aerosols, Lin et al [176] found that D 33 Sv alues correlated with concentrations of stratospherically-sourced 35 S, while D 36 Sanomalies Figure 7. Mass independent sulfur isotope effects observed in coal, tropospheric aerosols and SO 2 in the modern atmosphere.…”

Use of Isotope Effects To Understand the Present and Past of the Atmosphere and Climate and Track the Origin of Life

“…Using a state‐of‐the‐art analytical technique (originally developed by Brothers et al . and further improved by Lin and Thiemens), cosmogenic 35 S in aerosol samples can be measured in a high precision way and is demonstrated to be a sensitive chemical tracer for identification of air masses originating from high altitudes . By measuring all five sulfur isotopes ( 32 S, 33 S, 34 S, 35 S, and 36 S) in the same sulfate aerosols, Lin et al .…”

Vertically uniform formation pathways of tropospheric sulfate aerosols in East China detected from triple stable oxygen and radiogenic sulfur isotopes

“…The oxygen‐17 anomaly (Δ 17 O = δ 17 O‐0.52 × δ 18 O) in SO 4 2− is derived from the oxidants involved in its formation, providing an isotopic constraint for the relative importance of SO 4 2− formation pathways [ Lee et al , ; Lee and Thiemens , ; Lyons , ; Savarino et al , ; Savarino and Thiemens , ; Shaheen et al ., Vicars and Savarino , ] (see Text S1 and Table S1 in the supporting information for details). The radiogenic 35 S (half‐life = 87 days) is exclusively produced in the higher atmosphere by high‐energy cosmic rays [ Lal and Peters , ], and therefore, an enrichment of 35 S in the PBL is a direct measure of downward mixing of SO 2 /SO 4 2− from the FT (or the stratosphere) [ Lin et al , ; Priyadarshi et al , ; Priyadarshi et al , ]. Consequently, the coupled analysis of Δ 17 O and 35 S in the same SO 4 2− samples is a novel, unique, and powerful tool to gain formation chemistry (Δ 17 O) and source altitude ( 35 S) information of SO 4 2− from field‐based measurements [ Hill‐Falkenthal et al , ; Hill‐Falkenthal et al , ].…”

“…Lyons, 2001;Savarino et al, 2000;Savarino and Thiemens, 1999;Shaheen et al, 2013 Vicars andSavarino, 2014] (see Text S1 and Table S1 in the supporting information for details). The radiogenic 35 S (half-life = 87 days) is exclusively produced in the higher atmosphere by high-energy cosmic rays [Lal and Peters, 1967], and therefore, an enrichment of 35 S in the PBL is a direct measure of downward mixing of SO 2 /SO 4 2À from the FT (or the stratosphere) [Lin et al, 2016a;Priyadarshi et al, 2011a;Priyadarshi et al, 2012]. Consequently, the coupled analysis of Δ 17 O and 35 S in the same SO 4 2À samples is a novel, unique, and powerful tool to gain formation chemistry…”