Chemosphere 48 (2002) 981–992 www.elsevier.com/locate/chemosphere Levels and pattern of volatile organic nitrates and halocarbons in the air at Neumayer Station (70S), Antarctic Ralf Fischer a a,1 , Rolf Weller b, Hans-Werner Jacobi Karlheinz Ballschmiter a,* b,2 , Department of Analytical and Environmental Chemistry, University of Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany b Alfred-Wegener-Institute for Polar and Marine Research, Am Handelshafen 12 D-27570 Bremerhaven, Germany Received 13 February 2001; received in revised form 14 February 2002; accepted 28 February 2002 Abstract Levels and patterns of C1–C4/C9 organic nitrates were measured for the ﬁrst time in Antarctica. The sampling was done by adsorptive enrichment on Tenax TA followed by thermodesorption cold-trap high resolution capillary gas chromatography with electron capture detection. 2–70 l air on-column have been analyzed this way. C1–C9 alkyl mononitrates, C2–C4 alkyl dinitrates, C2–C4 hydroxy alkyl nitrates, and halocarbons could be identiﬁed in air samples collected near the German Neumayer Research Station, Antarctica, in February 1999. Volatile biogenic and anthropogenic halocarbons were used to assess the origin of the air parcels analyzed. The average concentration measured P for C2–C6 alkyl nitrates was in the range of 9:2 1:8 ppt(v), while the sum of the mixing ratios of six C2–C4 hydroxy alkyl nitrates was in the range of 1:1 0:2 ppt(v). Moreover, C2–C4 alkyl dinitrates were found at levels near the detection limit of 0.1–0.5 ppt(v). The concentrations of organic nitrates found in Antarctic air represent ultimate baseline levels due to chemical and physical loss processes during long-range transport in the air. The South Atlantic and the Antarctic Ocean as a general secondary source for organic nitrates in terms of an air/sea exchange equilibrium has to be evaluated yet, but it seems logical. Our results conﬁrm the common assumption that there are no biogenic marine sources of C2–C9 organonitrates. We have found a level of >80 ppt(v) for methyl nitrate. This level if it can be conﬁrmed in a systematic survey requires a strong biogenic source of methyl nitrate in the Antarctic Ocean. 2002 Elsevier Science Ltd. All rights reserved. Keywords: Alkyl mononitrates; Methyl nitrate; Hydroxy alkyl nitrates; Alkyl dinitrates; Air; Antarctica; Thermal desorption; Capillary gas chromatography; Baseline levels; Long-range transport 1. Introduction * Corresponding author. Tel.: +49-731-502-2750; fax: +49731-502-2763. E-mail address: email@example.com (K. Ballschmiter). 1 Present address: Dr. Th. B€ ohme KG, Isardamm 79-83, D82538 Geretsried. 2 Present address: Department of Hydrology and Water Research, 1133 E. North Campus Dr., University of Arizona, Tucson, AZ 85721-0011, USA. The troposphere has to be considered in general as an oxidative medium with the tendency for species to be converted to a more oxidized state. The results of the light induced photochemistry and oxidation chemistry of hydrocarbons in air depend on the levels of the reaction of starting radicals such as OH, or NO3 , and on the levels of trace gases like odd-nitrogen NOy , (particularly NOx (NO þ NO2 ) as main part), ozone, and organosulfur compounds (Atlas et al., 1992a,b; Carroll et al., 1992; Barrie et al., 1994; Kondo et al., 1997; Platt 0045-6535/02/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 0 4 5 - 6 5 3 5 ( 0 2 ) 0 0 1 1 0 - 8 982 R. Fischer et al. / Chemosphere 48 (2002) 981–992 and Le Bras, 1997). As a result of combustion emissions, levels of NOx greatly enhanced over those in the background troposphere can be found in urban and densely inhabited continental areas. NOx is the key in the organonitrogen chemistry of the urban troposphere. When NO and NO2 are present in sunlight, ozone formation occurs as a result of photolysis of NO2 at wavelength k < 424 nm. • Formation of alkyl radicals (initial step): RH þ OH ! R þ H2 O RH þ NO3 ð5aÞ ! R þ HNO3 ð5bÞ R0 RHC–O þ D ! R þ R0 HC@O 0 0 R ðC@OÞR þ hm ! R þ R C@O ð5cÞ ð5dÞ • Formation of peroxyalkyl radicals: NO2 þ hm ! NO þ Oð3 PÞ ð1Þ Oð3 PÞ þ O2 þ M ! O3 þ Mz ð2Þ On the other hand, ozone reacts with NO to regenerate NO2 . O3 þ NO ! NO2 þ O2 ð3Þ Therefore the steady-state ozone concentration is approximated by Eq. (4) ½O3 ¼ J1 ½NO2 k3 ½NO ð4Þ Expression (4) is named the photostationary state relation. The ozone concentration is in a ﬁrst approximation proportional to the NO2 =NO ratio, which means high NO2 levels lead to high ozone concentrations. Conversion of NO to NO2 by HO2 or peroxyalkyl radicals (7a) will lead to increases in ozone and deviation from Eq. (4). Members of the NOy pool are also involved in these processes by increasing or reducing NOx levels in the air. Alkyl nitrates as parts of the NOy pool are therefore of potential interest. Alkyl nitrates besides being compounds of the atmospheric chemistry are used as propellants, and explosives (K€ ohler and Meyer, 1995). Together with the alkyl nitrites they are a group of potent pharmaceuticals, e.g. isosorbid dinitrate is a powerful vasodilator (Ahlner et al., 1991). None of the technical and pharmaceutical uses leads however to a general environmental contamination. Local contaminations by explosives may occur. The source of alkyl nitrates in the troposphere is the conversion of hydrocarbons (Fraser et al., 1997). OH/O2 (5a) or NO3 /O2 (5b) attack on an aliphatic carbon– hydrogen or an oleﬁnic C@C bond forms peroxyalkyl radicals RO2 (6). They are also formed by a thermolysis/ O2 reaction (5c) of long chain alkoxy radicals and by the photolysis (5d) of carbonyl compounds followed by the addition of O2 . The reaction of peroxyalkyl radicals with NO leads to nitrogen dioxide and alkoxy radicals–– ﬁnally stabilizing as carbonyl compounds (7a) and (7b)––or in a side reaction to alkyl nitrates (reactions (7c)) (Atkinson et al., 1982; Finlayson-Pitts and Pitts, 1986; Atkinson, 1990; Seinfeld and Pandis, 1998). R þ O2 ðþ MÞ ! RO2 ðþ Mz Þ ð6Þ • Formation of stable products: RO2 þ NO ! RO þ NO2 RO þ O2 ! R1 R2 CO þ HO2 ð7aÞ ð7bÞ RO2 þ NOðþ MÞ ! ðRO2 NOÞðþ Mz Þ ! RONO2 ð7cÞ This reaction scheme may repeat itself with alkyl nitrates leading ﬁnally to carbonyl alkyl nitrates or to non-vicinal alkyl dinitrates. The reaction of alkenes with either OH during daytime or with NO3 during nighttime in the presence of NOx leads to the formation of multifunctional organic nitrates like hydroxy alkyl nitrates or alkyl dinitrates (O’Brien et al., 1995; O’Brien et al., 1997; Kastler and Ballschmiter, 1998; Kastler and Ballschmiter, 1999). Moreover, organic nitrates formed by the reaction of isoprene have recently been reported (Werner et al., 1999). A detailed summary of the reaction schemes leading to alkyl nitrates is given by Roberts (Roberts, 1990). The yield of alkyl nitrates in the branching of the reaction of a peroxyalkyl radical with NO (7c) increases from <0.014 for ethane to 0.33 for octane. Thus a wide range of homologues and isomeric alkyl nitrates is expected in the atmosphere. The decreasing concentrations of long-chain alkanes are partly oﬀset by the increased yields of alkyl nitrate formation (Atkinson et al., 1982; Schneider et al., 1998a). While for alkyl mononitrates 6 C5 the dominant loss process is photolysis (8) (Clemitshaw et al., 1997), alkyl nitrates with more than ﬁve C-atoms and multifunctional alkyl nitrates are mainly degraded by OH radicals (9) (Talukdar et al., 1997). • Atmospheric chemistry of alkyl nitrates RONO2 þ hm ! RO þ NO2 ð8Þ RONO2 þ OH ! multifunctional nitrates; polar products ð9Þ In continental air alkyl nitrates contribute 2% to the NOy budget, increasing up to 15% for marine air (Atlas et al., 1992a,b). They are a sink of the NOy pool par- R. Fischer et al. / Chemosphere 48 (2002) 981–992 ticularly during polar winters. Thus, in arctic air masses the alkyl nitrates can enrich up to 20% of the total NOy budget (Bottenheim et al., 1993). Photodegradation of alkyl nitrates results in the formation of NOx . They can act as an important NOx source in the polar regions with highest release rates of NOx during polar sunrise. Since the ﬁrst measurements of alkyl nitrates in the marine atmosphere 1988 by Atlas (Atlas, 1988), this class of compounds found increasing interest. Several studies took place in the USA, Canada and Germany. Moreover ﬁeld campaigns took place in the Paciﬁc air (equatorial and Hawaiian region) and the Atlantic air on board RV ‘‘Meteor’’ (Schneider and Ballschmiter, 1999) and RV ‘‘Polarstern’’ (Fischer et al., 2000). In spite of increasing activities in this ﬁeld of atmospheric chemistry the number of studies in polar regions is limited. Concentrations in the low ppt(v) range were found for the North Paciﬁc air by Atlas (Atlas et al., 1992a,b; Atlas et al., 1993). P Roberts measured concentrations of 14 8:3 ppt(v) for C1–C4 alkyl nitrates at Chebogue Point, Nova Scotia (Roberts et al., 1998). de Kock found mean concentrations of 17:5 8:4 ppt(v) for C3– C5 alkyl nitrates at the South African southeast coast (de Kock and Anderson, 1994). More P recently Schneider reported levels of 3–8 ppt(v) for C3–C5 alkyl nitrates for the South Atlantic air (Schneider, 1998a,b; Schneider and Ballschmiter, 1999). Fischer reported a mean conP centration of 1.7 ppt(v) for C4 þ C5 alkyl P nitrates for the North Atlantic air and 1.3 ppt(v) for C4 þ C5 for the South Atlantic air (Fischer, 1999; Fischer et al., 2000). Fischer gives a global overview on the levels of short chain alkyl nitrates at diﬀerent continental and marine sampling sites (Fischer and Ballschmiter, 2001). O’Brien reported 1995 for the ﬁrst time the occurrence of four alkyl hydroxy nitrates and one alkyl dinitrate (O’Brien et al., 1995; O’Brien et al., 1997). Recently additional hydroxy alkyl nitrates and 30 alkyl dinitrates were identiﬁed in urban air (Kastler and Ballschmiter, 1998; Kastler and Ballschmiter, 1999; Fischer et al., 2000). We believe to be the ﬁrst to present in this work levels and patterns of higher organic nitrates in the lower troposphere of the Antarctic. Furthermore we compare the occurrence of alkyl nitrates with the levels of halocarbons as atmospheric markers. A comparison with values obtained in South Atlantic air places the Antarctic data in a greater spatial context. 2. Short hand nomenclature of organic nitrates Schneider and Ballschmiter recently introduced a shorthand nomenclature of alkyl mononitrates that correlates the structure of a speciﬁc alkyl nitrate to the hydrocarbon precursor (Schneider and Ballschmiter, 983 1996). In our extended shorthand nomenclature the expression organic nitrates represents the whole family of mono- and multifunctional alkyl nitrates (Table 1) keeping the basic settings given by Schneider and Ballschmiter (Fischer et al., 2000). The longest unbranched alkyl chain is taken as the skeleton of the molecule; e.g. C7 means in this case that the longest unbranched carbon chain has seven Catoms. Furthermore we deﬁne for unbranched alkyl nitrates that the nitrooxy group possesses the highest priority and is numbered ﬁrst. For branched alkyl nitrates the alkyl side chains possess now the highest priority above all other groups in the molecule, and therefore the positions of alkyl side chains are numbered ﬁrst. M is used for methyl, and E is used for ethyl side chains, respectively. This convention is particularly important and helpful if isomeric hydrocarbon skeletons have to be distinguished. For a better understanding we explain the abbreviations introducing some examples for alkyl mononitrates, alkyl dinitrates, hydroxy alkyl nitrates, keto alkyl nitrates, and alicyclic alkyl nitrates. Alkyl mononitrates: 2,4M5C7 indicates a heptyl chain with two methyl groups at the 2 and 4 position and the nitrooxy group at the 5 position, speciﬁcally a 2,4-dimethyl-5-nitrooxyheptane. Alkyl dinitrates: 2,3M1,4C5 would be a alkyl dinitrate with a carbon skeleton of ﬁve atoms, with two methyl groups at the 2 and 3 position, and two nitrooxy groups at position 1 and 4, speciﬁcally a 2,3-dimethyl1,4-dinitrooxy pentane. Hydroxy alkyl nitrates: OH is used for the hydroxy group. 3OH1C4 would be 3-hydroxy-1-nitrooxy butane. Keto alkyl nitrate: The letter O labels the carbonyl group, e.g. 2O1C5 is a 2-keto-1-nitrooxy pentane. Alicyclic alkyl nitrates: The letters c and t are used for cis and trans positions, respectively. Cy indicates an alicyclic skeleton. c1,2CyC6 indicates a cis-1,2-dinitrooxy cyclohexane. Aryl alkyl nitrates: Aryl alkyl nitrates are named considering the phenyl- or naphthyl group as a substituent of the alkyl chain (Woidich et al., 1999). 3. Position of the Neumayer Research Station in the Antarctic The Neumayer Station (70390 S, 8150 W) was established in 1992 on the Ekstr€ om Shelf Ice as a research observatory for geophysical, meteorological and air chemistry measurements. Fig. 1 shows the geographical position of the research station. The snow-covered station is located on shelf ice that is 200 m thick and almost ﬂat. The shelf ice margin where supply ships (e.g. RV ‘‘Polarstern’’) dock is 10 km away. The isolated location 984 R. Fischer et al. / Chemosphere 48 (2002) 981–992 Table 1 IUPAC and short style nomenclature of the alkyl mononitrates and short-chain alkyl hydroxy- and dinitrates identiﬁed in the Antarctic air samples No. IUPAC Abbreviation Cn No. Alkyl mononitrates 1 2 3 4 5 6 7 8 IUPAC Abbreviation Cn Alkyl dinitrates Nitrooxy-methane Nitrooxy-ethane 1-Nitrooxy-propane 2-Nitrooxy-propane 1-Nitrooxy-butane 2-Nitrooxy-butane 2-Methyl-1-nitrooxy-butane 1-Nitrooxy-pentane 2-Nitrooxy-pentane C1 C2 1C3 2C3 1C4 2C4 2M1C3 1C5 2C5 3-Nitrooxy-pentane 2-Methyl-3-nitrooxy-butane 1-Nitrooxy-hexane 2-Nitrooxy-hexane 3-Nitrooxy-hexane 1-Nitrooxy-heptane 2-Nitrooxy-heptane 3-Nitrooxy-heptane 4-Nitrooxy-heptane 1-Nitrooxy-octane 3C5 2M3C4 1C6 2C6 3C6 1C7 2C7 3C7 4C7 1C8 2 3 4 5 6 3 4 5 6 1,2-Dinitrooxy-ethane 1,2-Dinitrooxy-propane 1,3-Dinitrooxy-propane 1,3-Dinitrooxy-butane 2,3-Dinitrooxy-butane 2-Methyl-1,2-dinitrooxy-propane 2,3-Dinitrooxy-pentane 2-Methyl-3,4-dinitrooxy-pentane Hydroxy alkyl nitrates 1,2C2 1,2C3 1,3C3 1,3C4 2,3C4 2M1,2C3 2,3C5 2M3,4C5 1-Hydroxy-2-nitrooxy-propane 2-Hydroxy-1-nitrooxy-propane 3-Hydroxy-2-nitrooxy-butane 4-Hydroxy-2-nitrooxy-butane 2-Hydroxy-1-nitrooxy-pentane 1-Hydroxy-2-nitrooxy-pentane 2-Hydroxy-3-nitrooxy-hexane 4-Hydroxy-3-nitrooxy-hexane 2-Methyl-4-hydroxy-5-nitrooxy-pentane 2-Methyl-5-hydroxy-4-nitrooxy-pentane 1OH2C3 2OH1C3 3OH2C4 4OH2C4 2OH1C5 1OH2C5 2OH3C6 4OH3C6 2M4OH5C5 2M5OH4C5 4. Experimental 4.1. Air sampling procedure Fig. 1. Geographical position of Neumayer Station; on the Ekstr€ om Shelf ice in the Atka Bay, Northeast Weddell Sea (703900 S, 81500 W). of the station makes it a valuable reference site for measurements under conditions of extreme air purity. In addition, the proximity to the ice margin permits the detection of substances released from the ocean to the atmosphere. Table 2 summarizes the meteorological parameters related to the Neumayer Station during the sampling period. The air sampling was done by pulling air through glass tubes (160 mm length, 3 mm, i.d.) ﬁlled with 80– 100 mg of Tenax TA, 60–80 mesh (Chrompack, Middelburg, Netherlands) at a ﬂow rate of 80–100 ml/min with a sampling pump (SKC model 222-3, Eighty Four, Pennsylvania, United States). Two sampling tubes connected in series have been used to control the sampling eﬃciency. Volumes of 2–68 l air were sampled. The sampling tubes were ﬂame-sealed in larger glass tubes for transport and were kept refrigerated until analysis. To detect the whole range of alkyl nitrates parallel sampling of low volumes of 2 l for C2 up to C5 alkyl nitrates and high volumes of 50–70 l as well for alkyl nitrates C > 5 is recommended. In polar regions the breakthrough loss due to sampling temperatures is negligible. 4.2. Analytical procedure: GC separation, detection and quantitation The high resolution gas chromatography with electron capture detection (HRGC/ECD) chromatographic separation was performed on a Chrompack Model 9001 gas chromatograph equipped with a thermal desorption cold trap (TCT) device (Chrompack, Middelburg, R. Fischer et al. / Chemosphere 48 (2002) 981–992 985 Table 2 Meteorological parameters related to the Antarctic air samples Sample Date Sample volume (l) Air temperature (C) Wind direction Wind velocity (m s1 ) Humidity (%) NM NM NM NM 13.02.1999 22.02.1999 22.02.1999 26.02.1999 2.0 30.2 68.0 10.8 7.5 5.5 10.0 6.3 130SE 75ENE 160ESE 90E 4 5 3 12 75 73 87 96 1 2 3 4 Netherlands). We used a DB-1701 capillary (58 m 0:312 mm i:d: 1:0 lm ﬁlm thickness, J&W Scientiﬁc, Folsom, United States). A detailed description of the analytical conditions is given in (Fischer et al., 2000). Quantitation was done by external calibration with solutions containing known amounts of alkyl nitrates and halocarbons. The limit of detection based on a 30 l air sample was about 0.3 ng/m3 or 0.05 ppt(v) for alkyl nitrates and 0.2 ng/m3 or 0.02 ppt(v) for the three halocarbons trichloroethane, tetrachloroethene and bromoform. The overall error for the alkyl nitrates and halocarbons was estimated to be less than 20% (Fischer, 1999). 5. Results The measured concentrations of organic nitrates and halocarbons of this work are summarized in Table 3. The results presented in this work are unique for organic nitrates. Table 4 lists all literature data and compares them with the results of this work. Highest in abundance are the short chain alkyl mononitrates C2, 1C3, 2C3 and 2C4. This observation is consistent with the literature data for Arctic regions (Table 4). The alkyl nitrate levels for the Arctic regions are one order of magnitude higher than the values found in the Antarctic, indicating that the sampling sites in the North are closer to the highly industrialized regions of the North American continent. In terms of the vicinity to non-point sources the Arctic and Antarctic regions have to be considered diﬀerently; the eﬀects of a limited photodegradation in the respective polar nights will be similar. Fig. 2a and b depict TCT–HRGC–ECD chromatograms of air samples collected at Neumayer Station, Antarctica. To our knowledge these are the ﬁrst chromatograms showing alkyl nitrates in the air of a South Polar region. The biogenic marker dibromomethane and tribromomethane (bromoform) show relative to alkyl nitrates higher mixing ratios indicating marine emissions sources (the sampling location is only 10 km away from the coastal line). Anthropogenic markers like carbontetrachloride and 1,1,1-trichloroethane with long kOH Table 3 Mixing ratios for the alkyl mononitrates, hydroxy alkyl nitrates, alkyl dinitrates, and bromo- and chloro-halocarbons in the Antarctic air in ppt(v) (n ¼ 2–4) Mononitrates Mean (ppt(v)) Hydroxy nitrates Mean (ppt(v)) Halocarbons Mean (ppt(v)) C1(n ¼ 1) C2 1C3 2C3 1C4 84 4.6 1.1 0.7 0.03 2OH1C4 2OH1C3 RR-3OH2C4a 1OH2C3/RS-3OH2C4a <LOD 0.03 0.3 0.8 Tetrachloromethane 1,1,1-Trichloroethane Trichlorethene Tetrachlorethene Hexachloroethane 95 75 <LOD 0.3 0.06 2C4/2M1C3 1C5 2C5 3C5 0.5 0.7 <LOD 0.03 1OH2C4 3OH1C4 P OH 0.02 0.01 1.1 Dibromomethane Bromodichloromethane Dibromochloromethane Bromoform 1,2-Dibromoethane 0.8 0.05 0.02 0.3 0.1 Dinitrates 1C6 2C6 3C6 2C7 4C7 0.5 1.0 0.08 0.18 0.02 1,2C3/1,2C2 2M1,2C3 0.5 0.1 P C4 þ C5 P C3–C6 1.3 4.6 Limit of detection ðLODÞ ¼ 0:01 ppt(v). a RR/SS-3OH2C4; RS/SR-3OH2C4 co-elution with 1OH2C3. 986 R. Fischer et al. / Chemosphere 48 (2002) 981–992 Table 4 Comparison of mixing ratios of alkyl nitrates in the Antarctic air with Arctic and Alaska reference data in ppt(v) Antarctic (this work) b 1C3 2C3 1C4 2C4/2M1C3 2M3C4 1C5 2C5 3C5 2C6 3C6 2C7 3C7 P C2–C6 P C3–C7 1.11 0.49 0.03 0.48 <LOD 0.71 <LOD 0.03 0.08 0.95 0.18 (0.01) 9.2 – Arctic, Canadaa Alert, Canada b Polar night Polar day 3.33 12.44 1.7 18.41 4.84 1.01 5.44 4.31 2.46 4.27 1.45 1.86 – – 3.14 13.08 1.18 13.73 2.32 0.53 2.47 2.31 0.98 1.65 0.56 0.68 – – 3.96 12.5 2.05 13.98 2.65 1.03 4.18 3.02 1.50 2.55 – – 34c 144d Limit of detection ðLODÞ ¼ 0:01 ppt(v). a Canadian Arctic (69N–83N) ‘‘Polar Sunrise Experiment’’ April 1992 (Leaitch et al., 1994). b Alert, Northwest Territories of Canada, ‘‘Polar Sunrise Experiment’’ January–April 1992, Polar night January–March; day period March–April (Muthuramu et al., 1994). c Poker Flat Research Rang, Alaska (64N/147W) winter/spring 1993 (Beine et al., 1996). d Canadian Arctic March–April 1988 (Bottenheim et al., 1993). lifetimes (s ¼ month to years) were also found, but markers with short kOH lifetime like trichloroethene (s ¼ 7 days) are below the limit of detection (<0.01 ppt(v)). The patterns of the Antarctic air samples are quite similar to the patterns found in the South Atlantic Trade Wind region. Fig. 2c depicts for comparison a chromatogram of this marine region, taken during the ALBATROSS campaign on board of RV ‘‘Polarstern’’ (ANT XIV/1) at 10.4S/25.5W (Fischer et al., 2000). The Antarctic and the Southern Trades apparently represent baseline levels of clean marine air in terms of organic nitrates. a mean value of 0.3 ppt(v). During the Albatross– Campaign we found similar mixing ratios in the South Atlantic Ocean and levels by a factor 3 higher for the North Atlantic (Fischer et al., 2000). The good correlation of the measured halocarbon ratios with literature data backs the accuracy of our analytical procedure. 6. Discussion To interpret the data of the South Polar region in a wider spatial context we enclose the data of the Albatross–Campaign, which also covered the South Atlantic (Fischer et al., 2000). 5.1. Levels of anthropogenic halocarbons in Antarctic air 6.1. Levels of butyl nitrates in marine and Antarctic air The mixing ratios for the long-lived halocarbons (Table 3) are in good agreement with earlier measurements. We found 95 ppt(v) for tetrachloromethane (s ¼ 42a) while Derwent measured 101 ppt(v) in Ireland (Derwent et al., 1998). This indicates a more or less even global distribution in the troposphere. For 1,1,1-trichlorethane we observed 75 ppt(v) (s ¼ 4:8a); estimations by Derwent for 1999 results in ratios of 70–80 ppt(v) (Derwent et al., 1998). The situation seems to be similar as observed for tetrachloromethane. The mean value for hexachloroethane is in the range of 0.06 ppt(v) and somewhat lower than 0.24 ppt(v) observed by Atlas in 1993 for the Paciﬁc (Atlas et al., 1993). For medium lived C 2 halocarbons like tetrachlorethene we observed Fig. 3 is a plot of the mixing ratios of the 2C4, the secondary, and the 1C4, the primary butyl nitrate along the Atlantic Ocean (Albatross–Campaign) and at Neumayer Station, Antarctic. The main emission sources are in the industrialized areas of the Northern hemisphere. The accumulation in the Northern hemisphere is enhanced in fall and wintertime by a reduced photodegradation. The concentration for 2-butyl nitrate (2C4) in the coastal region is 3.5–5 ppt(v). An average value of 1 0:2 ppt(v) is observed for 1-butyl nitrate (1C4) in the air of the North Atlantic. A 2C4/1C4 ratio close to 4 indicates a recent continental input or marine local input by islands. R. Fischer et al. / Chemosphere 48 (2002) 981–992 987 Fig. 2. (a) TCT–HRGC(DB-1701)/ECD chromatogram of an Antarctic air sample, taken at Neumayer Station, sampling and oncolumn volume (a) 2.0 l (sample NM 1), (b) 68 l (sample NM 3). (c) TCT–HRGC(DB-1701)/ECD chromatogram of a South Atlantic air sample of the trade wind region 10.4S/25.5W, sampling and on-column volume 105 l. 988 R. Fischer et al. / Chemosphere 48 (2002) 981–992 masses. It is the 2-butyl-, 2-pentyl nitrate/tetrachloroethene quotient (traﬃc/industry indicator) and the ratio of isomeric pentyl nitrates (traﬃc indicator). 6.3. The 2-butyl-, 2-pentyl nitrate/tetrachlorethene ratio as an air mass marker Fig. 3. Distribution of butyl nitrates from 67N to 70S over the Atlantic Ocean mainly across 30W longitude (Albatross– Campaign on board RV Polarstern ANT XIV/1, 1996) and at the Neumayer Station, 1999. In the South Atlantic trade wind region the values for 2C4 decrease to 0:2 0:05 ppt(v) leading to a 2C4/1C4 ratio to about 1 and even below 1. The levels of 2C4 rise again to 0:4 0:08 ppt(v) in the west wind belt of the South Atlantic and remain at 0:4 0:1 ppt(v) for air collected at the Neumayer Station. The levels of 1C4 decrease from 1:0 0:2 ppt(v) in the Northern hemisphere passing the intertropical convergence zone (ITCZ) to the south to levels of 0:4 0:08 ppt(v). A further decrease to levels down to the limit of detection of 0.05 ppt(v) is observed for the air at the Neumayer Station. The 2C4/1C4 ratio covers a span between 0.2 and 7.0 reﬂecting in one part the dominance of 1C4 in ‘‘old’’ air masses and also a very low level of possible local input in the Antarctic. In the latter case only the dominant 2C4 would be detected. 6.2. Characterization of the age of air masses An air mass is called ‘‘young’’ if pollution deriving from densely inhabited regions with a corresponding level of traﬃc and industrial emissions is observed. Several attempts have been made to characterize air mass ages. Atherton used a pure deductive kinetic model (Atherton, 1989). Other models consider diﬀerences in photochemical degradation velocities using pairs of molecules or groups of molecules like carbon monoxide and alkyl nitrates (Roberts et al., 1996), PAN and alkyl nitrates (Buhr et al., 1990), hydrocarbons and alkyl nitrates (Roberts et al., 1998), NOy and NOx (Trainer et al., 1991), two isomeric alkyl nitrates (Flocke et al., 1998; Schneider and Ballschmiter, 1999) or consider the presence of benzyl nitrate (Schneider et al., 1998a; Schneider and Ballschmiter, 1999). Here we present two diﬀerent approaches to characterize the ‘‘age’’ of air Here, we present a method based on the diﬀerences in the degradation rates of short chain alkyl nitrates and semi-stable halocarbons (e.g. tetrachloroethene). Short chain alkyl nitrates are formed in all regions with traﬃc that are releasing signiﬁcant NO and short chain hydrocarbon emissions. Butyl- and pentyl nitrates are degraded by photolysis and OH on their long-range transport ﬁnally reaching remote areas like the Antarctic. The anthropogenic halocarbons emerge basically from industrialized continental regions and then undergo photochemistry on their long-range transport. They are degraded mainly by OH radicals and only to a minor extent by photolysis (Class and Ballschmiter, 1986). The kOH lifetime of tetrachloroethene is in the range of 4 month. Tetrachloroethene shows a three-step decrease in the global mixing ratios in the lower troposphere (Wiedmann et al., 1994). A ﬁrst decrease is observed when going from continental air to marine air of the Northern hemisphere. This is a mixture of a decrease by degradation and by mixing of the source air with less polluted air of the Northern Hadley cell of the general circulation. The second decrease is observed in the Northern tropics and a third one when passing the ITCZ reaching the air of South East Trades of the Southern hemisphere. This clearly indicates the separation of the air masses of both hemispheres in the lower troposphere by the ITCZ. This has been observed for other anthropogenic volatile chlorocarbons before (Class and Ballschmiter, 1986). The butyl nitrates do not give this clear diﬀerence in atmospheric levels but decrease more or less continuously in going to remote regions. The increased levels around the Azores indicate the importance of quasilocal inputs in the marine atmosphere due to traﬃc on these islands. Fig. 5a depicts the ratios of the mixing ratios of the secondary alkyl nitrates 2-butyl- and 2pentyl nitrate relative to tetrachloroethene (C2 Cl4 ) in the air of the Atlantic Ocean and in the air of Neumayer Station. Three clusters are formed. Marine air inﬂuenced by air masses coming from the South American continent is characterized by a surplus of 2-butyl and 2-pentyl nitrates relative to tetrachloroethene. Unpolluted marine air has low mixing ratios for 2-pentyl nitrate itself and the ratio 2C5/C2 Cl4 is <1 indicating a strong degradation for 2-pentyl nitrate. The third cluster represents the global baseline level. It is characterized by the fact that both the ratios for 2C4/C2 Cl4 and 2C5/C2 Cl4 R. Fischer et al. / Chemosphere 48 (2002) 981–992 are well below 1. This third cluster represents the photochemically aged pollution depleted air masses. 6.4. The ratio of isomeric pentyl nitrates as an air mass marker A further method to decide about the origin or age of an air parcel is to compare the levels of the isomeric pentyl nitrates. In the case of pentyl nitrates signiﬁcantly increased mixing ratios for primary and secondary pentyl nitrates are found with a surplus of secondary pentyl nitrates (3C5 > 2C5 > 1C5). Very low concentrations of secondary pentyl nitrates, and in contrast noticeably higher concentrations of 1-pentyl nitrates characterize aged air masses (e.g. collected in remote marine or Antarctic regions). The former sequence of the levels in air 3C5 > 2C5 > 1C5 turns now to 1C5 3C5 > 2C5. The mixing ratio for 2C5 in the air of the Antarctic Neumayer Station is below the limit of detection (Table 3). The missing of 2C5 and barely detectable traces of 3C5 while 1C5 can be measured conﬁrm that highly degraded air masses were collected. 6.5. Methyl nitrate in Antarctic air The level found for methyl nitrate found in the Antarctic is unexpectedly high and requires a speciﬁc discussion. The branching ratio for the atmospheric reaction Eqs. (7a)–(7c) is normally set close to zero for C1. Degradation of peroxyacetylnitrate (PAN) by the loss of CO2 or the esterﬁcation of methanol with nitric acid on aerosols (Senum et al., 1986; Orlando et al., 1992; Fan et al., 1994) can result in higher yields of metyl nitrate in polluted continental air. The reaction of methyl nitrate with OH is the major loss process. The reaction rate constant was ﬁrst measured by Gaﬀney et al. (Gaﬀney et al., 1986). It has recently be redetermined (Kakesu et al., 1997). Methyl nitrate is very volatile and substantial breakthrough losses will occur if not speciﬁc precautions (low sample volume, high amount of adsorbent, low temperature) are set to sample this very volatile alkyl nitrate by adsorption techniques. A correct quantitation of methyl nitrate is therefore diﬃcult and requires optimized sampling conditions. We have found a level of >80 ppt(v) for methyl nitrate in the low volume sample. Co-elution with other compounds in the gas chromatogram of our sample can be excluded by identiﬁcation of the C1 peak by HRGC/MSD. Recently Jones measured methyl nitrate from 27 to 46 ppt(v) and ethyl nitrate from 5 to 13 ppt(v) sampled at Neumayer Station 1997 (Jones et al., 1999). Walega et al. found for methyl nitrate 4 ppt(v) at Mauna Loa, Hawaii (Walega et al., 1992) and Flocke 989 et al. measured 8 ppt(v) in the air over the North Atlantic (Flocke et al., 1998). Atlas supposed a marine emission source for methyl nitrate (Atlas et al., 1997). In the marine boundary layer (MBL) maximum concentrations were found as high as 50 ppt(v) near Christmas Island (1–3N) and concentrations of 20–35 ppt(v) near Western Samoa (13S) during ACE 1 (Blake et al., 1999). The authors conclude that methyl nitrate has a signiﬁcant equatorial marine source. The most logic biogenic source would be the methylation of nitrate ions. We may observe a similar reaction for the nitrate ion leading to methyl nitrate as it is found for the methylation of chloride (Urhahn and Ballschmiter, 1998). Methionine methyl sulfonium chloride (MMSL) e.g. gave an intense release of monohalomethanes when mixed in a buﬀer with potassium halides. 6.6. Levels of hydroxy alkyl nitrates in marine and Antarctic air Fig. 4 is a plot of the mixing ratios of hydroxy alkyl nitrates along the Atlantic Ocean (Albatross–Campaign) and at Neumayer Station, Antarctic. All of the observed compounds are vicinal hydroxy alkyl nitrates. Hence, their formation pathway via OH radical addition to oleﬁns is most likely. We observe a NH/SH gradient of about factor 3 with 4:3 0:8 ppt(v) for the sum of 4 hydroxy alkyl nitrates in the air of the Northern hemisphere and 1:6 0:3 ppt(v) in the South Atlantic air. The mixing ratio for hydroxy alkyl nitrates in the air of the Neumayer Station is with 1:2 0:2 ppt(v) somewhat lower than in the South Atlantic air. In accordance with previous discussions the formation of secondary alkyl radicals is preferred to the formation of primary ones (Kastler, 1999). Therefore, if 1-alkenes are degraded by OH radicals, the yield of 1-hydroxy-2-nitrooxy-alkanes must be higher than the yield for 2-hydroxy-1-nitrooxy alkanes. This is consistent with our observations. Fig. 4. Distribution of hydroxy propyl- and butyl nitrates from 67N to 70S over the Atlantic Ocean and at Neumayer Station. 990 R. Fischer et al. / Chemosphere 48 (2002) 981–992 6.7. Principal compound analysis (PCA) of organic nitrates in marine and Antarctic air The principal compound analysis is a statistical model to compare the pattern of air samples between diﬀerent regions. The theoretical feedback of the method is given in (Smith, 1991). The n-dimensional expression is reduced to a two dimensional expression. The distance between two points is a measure of the similarity of air samples. Fig. 5b depicts the PCA of all marine and Antarctic air samples. 15 locations and the ratios of 14 alkyl mononitrates are the basis for the PCA given here. A grouping of air masses is also obtained by plotting two ratios of selected air constituents. This approach has been used to characterize air masses by their complex pattern of polychlorinated biphenyls (PCBs) (Schreitm€ uller et al., 1994). We have plotted here the ratios of the mixing ratio of 2-butyl nitrate/tetrachloroethene versus 2-pentyl nitrate/tetrachlorethene. The results are given in Fig. 5a. Three clusters of air masses can be diﬀerentiated. Cluster I contains all sampling locations representing global baseline levels. Cluster II summarizes marine air samples with slightly polluted air, indi- cating the inﬂuence of islands. The last cluster contains polluted air coming in from the South American continent. The PCA as an independent method conﬁrms the characterization of marine and polar air samples as discussed above. 7. Conclusion In this paper we presented for the ﬁrst time a data set of higher organic nitrates in the air of the German South Polar Neumayer Station. We are in a unique position to discuss and compare the levels and patterns of alkyl nitrates and halocarbons in the air of the Atlantic Ocean and in the air of the South Polar region. The organonitrate concentrations in the marine and Antarctic samples reached only 1–10% of the continental samples. The mixing ratio in the South East Trade Wind region and in the air of Neumayer Station are similar and represents the global baseline level for the organonitrates. This is a strong indication for the long-range transport of these molecules. No new alkyl nitrate formation is expected due to the lack of NOx sources in the marine and the Antarctic atmosphere. Methyl nitrate seems to be the exception from this rule. A biogenic source for this compound appears to be likely as it has been discussed before. Halocarbons can be used as marker molecules to distinguish between inhabited and biogenic sources. The ratio of tetrachloroethene to secondary alkyl nitrates can be used as a tool to decide about the origin and age of an air parcel analyzed. The ratio of the isomeric pentyl nitrates can also be used to characterize air masses. References Fig. 5. Grouping of air masses by (a) mixing ratio of 2-butyl nitrate/tetrachloroethene versus 2-pentyl nitrate/tetrachlorethene, (b) PCA of organic nitrates in marine air. Ahlner, J., Andersson, R.G.G., Torfgard, K., Axelsson, K.L., 1991. Organic nitrate esters: Clinical use and mechanisms of actions. Pharmacol. Rev. 43, 351–353. Atherton, C.S., 1989. Organic nitrates in remote marine environments: evidence for long- range transport. Geophys. Res. Lett. 16, 1289–1292. Atkinson, R., 1990. Gas-phase tropospheric chemistry of organic compounds: a review. Atmos. Environ. 24A, 1–41. Atkinson, R., Aschmann, S.M., Carter, W.P.L., Winer, A.M., Pitts, J.N., 1982. Alkyl nitrates formation from the NOx -air photooxidations of C2–C8 n-alkanes. J. Phys. Chem. 86, 4563–4569. Atlas, E., 1988. Evidence for >C3 alkyl nitrates in rural and remote atmospheres. Nature 331, 426–428. Atlas, E., Flocke, F., Schauﬄer, S., Stroud, V., Blake, D., Rowland, F.S., Singh, H., 1997. Evidence for marine sources of atmospheric alkyl nitrates: measurements over the tropical Paciﬁc Ocean during PEM tropics. Posterbeitrag, American Geophysical Union (AGU) 78 (46) Fall Meeting, Supplement. R. Fischer et al. / Chemosphere 48 (2002) 981–992 Atlas, E., Pollock, W., Greenberg, J., Heidt, L., 1993. Alkyl nitrates, nonmethane hydrocarbons and halocarbon gases over equatorial Paciﬁc Ocean during Saga 3. J. Geophys. Res. 98, 16 933–16 947. Atlas, E., Ridley, B.A., H€ ubler, G., Walega, J.G., Carroll, M.A., Montzka, D.D., Huebert, B.J., Norton, R.B., Grahek, F.E., Schauﬄer, S., 1992a. Partitioning and budget of NOy species during the Mauna Loa Observatory Photochemistry Experiment. J. Geophys. Res. 97, 10 449–10 462. Atlas, E., Schauﬄer, S.M., Merrill, J.T., Hahn, J., Ridley, B.A., Walega, J.G., Greenberg, J., Heidt, L., Zimmerman, P.B., 1992b. Alkyl nitrate and selected halocarbon measurements at Mauna Loa Observatory, Hawaii. J. Geophys. Res. 97, 10 331–10 348. Barrie, L.A., Li, S.M., Toom, D.L., Landsberger, S., Sturges, W.T., 1994. Lower tropospheric measurements of halogens, nitrates, and sulphur oxides during Polar Sunrise Experiment 1992. J. Geophys. Res. 99, 25 453–25 467. Beine, H.J., Jaﬀe, D.A., Blake, D.R., Atlas, E., Harris, J., 1996. Measurement of PAN, alkyl nitrates, ozone, and hydrocarbons during spring in interior Alaska. J. Geophys. Res. 101, 12 613–12 619. Blake, N.J., Blake, D.R., Wingenter, O.W., Sive, B.C., Kang, C.H., Thornton, D.C., Bandy, A.R., Atlas, E., Flocke, F., Harris, J.M., Rowland, F.S., (1999). Aircraft measurements of the latitudinal, vertical, and seasonal variations of NMHCS, methyl nitrate, methyl halides, and DMS during the ﬁrst aerosol characterization experiment. (ACE 1) J. Geophys. Res. 104, 21 803-21 817. Bottenheim, J.W., Barrie, L.A., Atlas, E., 1993. The partitioning of nitrogen oxides in the lower Arctic troposphere during spring 1988. J. Atmos. Chem. 17, 15–27. Buhr, M.P., Parrish, D.D., Norton, R.B., Fehsenfeld, F.C., Sievers, R.E., 1990. Contribution of organic nitrates to the total reactive nitrogen budget at a rural Eastern US site. J. Geophys. Res. 95, 9809–9816. Carroll, M.A., Ridley, B.A., Montzka, D.D., H€ ubler, G., Walega, J.G., Norton, R.B., Huebert, B.J., Grahek, F.E., 1992. Measurements of nitric oxide and nitrogen dioxide during the Mauna Loa Observatory Photochemistry Experiment. J. Geophys. Res. 97, 10 361–10 374. Class, T., Ballschmiter, K., 1986. Chemistry of organic traces in air VI: distribution of chlorinated C1–C4 hydrocarbons in air over the northern and Southern Atlantic Ocean. Chemosphere 15, 413–427. Clemitshaw, K.C., Williams, J., Rattigan, O.V., Shallcross, D.E., Law, K.S., Cox, R.A., 1997. Gas-phase ultraviolet absorption cross-sections and atmospheric lifetimes of several C2–C5 alkyl nitrates. J. Photochem. Photobiol A: Chem. 102, 117–126. de Kock, A.C., Anderson, C.R., 1994. The measurement of C3– C5 alkyl nitrates at a coastal sampling site in the Southern hemisphere. Chemosphere 29, 299–310. Derwent, R.G., Simmonds, P.G., O’Doherty, S., Ryall, D.B., 1998. The impact of the Montreal protocol on halocarbon concentrations in Northern hemisphere baseline and European air masses at Mace Head, Ireland over a ten year period from 1987–1996. Atmos. Environ. 32, 3689–3702. Fan, S.M., Jacob, D.J., Mauzerall, J.D., Bradshaw, D., Sandholm, S.T., Blake, D., Singh, H.B., Talbot, R., Gregory, G.L., Sachse, G.W., 1994. Origin of tropospheric 991 NOx over subarctic Eastern Canada in summer. J. Geophys. Res. 99, 16 867–16 877. Finlayson-Pitts, B.J., Pitts Jr., J.N., 1986. Atmospheric Chemistry: Fundamentals and Experimentals Techniques. John Wiley & Sons, New York. Fischer, R.G., 1999. Vorkommen und Umweltverhalten der C1 –C10 organischen Nitrate in kontinentaler und mariner Luft. Dissertation Dr. rer. nat., Universit€at Ulm. Fischer, R.G., Ballschmiter, K., 2001. Global occurrence and pattern of short chain alkyl nitrates. In: Proceedings Symposium Atmospheric Reactive Compounds. Bayreuth 1999, in press. Fischer, R.G., Kastler, J., Ballschmiter, K., 2000. Levels and pattern of alkyl nitrates, multifunctional alkyl nitrates, and halocarbons in the air over the Atlantic Ocean. J. Geophys. Res. 105, 14 473–14 494. Flocke, F., Volz-Thomas, A., Buers, H.J., P€atz, H.W., Garthe, H.J., Kley, D., 1998. Long-term measurements of alkyl nitrates in Southern Germany 1. General behavior and seasonal and diurnal variation. J. Geophys. Res. 103, 5729– 5745. Fraser, M.P., Cass, G.R., Simoneit, B.R.T., Rasmussen, R.A., 1997. Air quality model evaluation data for organics 4. C2 – C36 non-aromatic hydrocarbons. Environ. Sci. Technol. 31, 2356–2367. Gaﬀney, J.S., Fajer, R., Senum, G.I., Lee, J.H., 1986. Measurement of the reactiviy of OH with methyl nitrate: implication for prediction of alkyl nitrate–OH reaction rates. Int. J. Chem. Kinetics 18, 399–407. Jones, A.E., Weller, R., Minikin, A., Wolﬀ, S., Sturges, W.T., McIntyre, M.E., Leonard, S.R., Schrems, O., Bauguitte, S., 1999. Oxidized nitrogen chemistry and speciation in the Antarctic troposphere. J. Geophys. Res. 104, 21 355– 21 366. Kakesu, M., Bandow, H., Takenaka, N., Maeda, Y., et al., 1997. Kinetic measurements of methyl and ethyl nitrate reactions with OH radicals. Int. J. Chem. Kinetics 29, 933– 941. Kastler, J., 1999. Analytik, Massenspektrometrie und Vorkommen multifunktioneller Alkylnitrate in belasteter und unbelasteter Atmosph€are. Dissertation Dr. rer. nat., Universit€at Ulm. Kastler, J., Ballschmiter, K., 1998. Bifunctional alkyl nitrates––trace constituents of the atmosphere. Fresenius J. Anal. Chem. 360, 812–816. Kastler, J., Ballschmiter, K., 1999. Identiﬁcation of alkyl dinitrates in ambient air of Central Europe. Fresenius J. Anal. Chem. 363, 1–4. K€ ohler, J., Meyer, R., 1995. Explosivstoﬀe. VCH, Weinheim. Kondo, Y., Koike, M., Kawakami, S., Singh, H.B., Nakajiama, H., Gregory, G.L., Blake, D.R., Sachse, G.W., Merrill, J.T., Newell, R.E., 1997. Proﬁles and partitioning of reactive nitrogen over Paciﬁc Ocean in winter and early spring. J. Geophys. Res. 102, 28 405–28 424. Leaitch, W.R., Barrie, L.A., Bottenheim, J.W., Li, S.M., Shepson, P.B., Muthuramu, K., Yokouchi, Y., 1994. Airborne observations related to ozone depletion at Polar Sunrise. J. Geophys. Res. 99, 25 499–25 517. Muthuramu, K., Shepson, P.B., Bottenheim, J.W., Jobson, B.T., Niki, H., Anlauf, K.G., 1994. Relationsships between organic nitrates and surface ozone destruction during Polar 992 R. Fischer et al. / Chemosphere 48 (2002) 981–992 Sunrise Experiment 1992. J. Geophys. Res. 99, 25 369– 25 378. O’Brien, J.M., Shepson, P.B., Muthuramu, K., Hao, C., Hastie, D.R., 1995. Measurement of alkyl and multifunctional organic nitrates at a rural site in Ontario. J. Geophys. Res. 100, 22 795–22 804. O’Brien, J.M., Shepson, P.B., Wu, Q., Biesenthal, T.A., Bottenheim, J.W., Wiebe, H.A., Anlauf, K.G., Brickell, P., 1997. Production and distribution of organic nitrates, and their relationship to carbonyl compounds in an urban environment. Atmos. Environ. 31, 2059–2069. Orlando, J.J., Tyndall, G.S., Calvert, J.G., 1992. Thermal decomposition pathways for peroxyacetyl nitrate (PAN)–– implications for atmospheric methyl nitrate levels. Atmos. Environ. Part A––General Topic 17, 3111–3118. Platt, U., Le Bras, G., 1997. Inﬂuence of DMS on the Ox –NOy partitioning and the NOx distribution in the marine background atmosphere. Geophys. Res. Lett. 24, 1935–1938. Roberts, J.M., 1990. The atmospheric chemistry of organic nitrates. Atmos. Environ. 24A, 243–287. Roberts, J.M., Bertman, S.B., Parrish, D.D., Fredrick, C., Fehsenfeld, F.C., Jobson, B.T., Niki, H., 1998. Measurement of alkyl nitrates at Chebogue Point, Nova Scotia during the 1993 North Atlantic Regional Experiment (NARE) intensive. J. Geophys. Res. 130, 13 569–13 580. Roberts, J.M., Parrish, D.D., Norton, R.B., Bertman, S.B., Holoway, J.S., Trainer, M., Fehsenfeld, F.C., Carroll, M.A., Albercook, G.M., Wang, T., Forbes, G., 1996. Episodic removal of NOy species from the marine boundary layer over the North Atlantic. J. Geophys. Res. 101, 28 947– 28 960. Schneider, M., Ballschmiter, K., 1996. Separation of diastereomeric and enantiomeric alkyl–nitrates––systematic approach to chiral discrimination on cyclodextrin LIPODEX-D. Chem. Eur. J. 2, 539–544. Schneider, M., Ballschmiter, K., 1999. C3–C14 alkyl nitrates in remote South Atlantic air. Chemosphere 38, 233–244. Schneider, M., Deissler, A., Ballschmiter, K., 1998a. Levels and patterns of C1–C15 alkyl nitrates, perchloroethene, and bromoform in Californian air. ACS, Division of Environmental Chemistry Reprints of Extended Abstracts 38, 18– 20. Schneider, M., Luxenhofer, O., Deissler, A., Ballschmiter, K., 1998b. C1 –C15 alkyl nitrates, benzyl nitrate, and bifunctional nitrates: measurements in Californian and South Atlantic Air and global comparison using C2 Cl4 and CHBr3 as marker molecules. Environ. Sci. Technol. 32, 3055–3062. Schreitm€ uller, J., Vigneron, M., Bacher, R., Ballschmiter, K., 1994. Pattern analysis of polychlorinated biphenyls (PCB) in Marine Air of the Atlantic Ocean. Int. J. Environ. Anal. Chem. 57, 33–52. Seinfeld, J.H., Pandis, S.N., 1998. Atmospheric Chemistry and Physics––From Air Pollution to Climate Change. John Wiley & Sons, New York. Senum, G.I., Fajer, R., Gaﬀney, J.S., 1986. Fourier transform infrared spectroscopic study of the thermal stability of peroxyacetyl nitrate. J. Phys. Chem. 90, 152–156. Smith, G.L., 1991. Principal component analysis. an introduction. Anal. Proc. 28, 150–151. Talukdar, R.K., Burkholder, J.B., Hunter, M., Gilles, M.K., Roberts, J.M., Ravishankara, A.R., 1997. Atmospheric fate of several alkyl nitrates: part 2 UV absorption cross-sections and photodissoziation quantum yields. J. Chem. Soc. Farad. Trans. 93, 2797–2805. Trainer, M., Buhr, M.P., Curran, C.M., Fehsenfeld, F.C., Hsie, E.Y., Liu, S.C., Norton, R.B., Parrish, D.D., Williams, E.J., 1991. Observations and modeling of the reactive nitrogen photochemistry at a rural site. J. Geophys. Res. 96, 3045– 3063. Urhahn, T., Ballschmiter, K., 1998. Chemistry of the biosynthesis of halogenated methanes: C1-organohalogens as pre-industrial chemical stressors in the environment? Chemosphere 37, 1017–1032. Walega, J.G., Ridley, B.A., Madronich, S., Grahek, F.E., Shetter, J.D., Sauvain, T.D., Hahn, J., Merill, J.T., Bodhaine, B.A., Robinson, E., 1992. Observations of peroxyacetyl nitrate, peroxypropionyl nitrate, methyl nitrate and ozone during Mauna Loa Observatory Photochemistry Experiment. J. Geophys. Res. 97, 10 311–10 330. Werner, G., Kastler, J., Looser, R., Ballschmiter, K., 1999. Organic nitrates of isoprene as atmospheric compounds. Angew. Chem. Int. Ed. 38, 1634–1637. Wiedmann, T.O., G€ uthner, B., Class, T., Ballschmiter, K., 1994. Global distribution of tetrachloroethene in the troposphere: measurements and modeling. Environ. Sci. Technol. 28, 2321–2329. Woidich, S., Froescheis, O., Luxenhofer, O., Ballschmiter, K., 1999. EI and NCI-mass spectrometry of arylalkyl nitrates and their occurrence in urban air. Fresenius J. Anal. Chem. 364, 91–99.
* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project