Long‐term observation of nitrate radicals at the Tor Station, Kap Arkona (Rügen)

Abstract

Long-term observation of the trace gases NOa, ozone, and nitrate radicals (NO3) at a rural site in the Baltic Sea (near Kap Arkona, island Riigen) using differential optical absorption spectroscopy (DOAS) are presented here. The time series of these species cover more than 14 months of data. Additionally, meteorological data were taken from the Deutscher Wetterdienst station at Kap Arkona. The average nighttime NO3 concentration was determined at 7.8 ppt. Maximum lifetimes of more than 5000 s were observed, but average NO3 lifetimes are close to 250 s. As nitrate radicals are expected to play an important role in the nonphotochemical conversion of NOx to HN03, long-term observations offer a key for investigation of possible sink mechanisms of NO3 molecules mediated by both homogeneous and heterogeneous reactions. Analysis of the data shows that the NO3 lifetime is inversely proportional to the NOa concentration, thus suggesting that the removal of N20s is actually the dominating NO3 loss process. The mean N205 concentration from this long-term measurement was calculated at 1 ppb with an N20s lifetime between 1000 s and 20000 s covering 90 • of the data. Platt et al., [1980] and Nozon et al., [1980], nitrate radicals are being recognized as key intermediates in a growing list of important chemical processes in the atmosphere (e.g., see Figure 1). It became clear that the NO3 radical plays an important role in the nonphotochemical conversion of NOx to HNOa via heterogeneous hydrolysis of N205 formed in the NOa-NO2combination [Platt et al., 1979; Ehhalt et al., 1982; Richards, 1983; Heikes and Thompson, 1983; Calvert and Stockwell, 1983; Jones et al. 1983; Canttell et al., 1985; Platt et al., 1985,' Russel et al., 1985; 1986; Parrish et al., 1993; Dentenet and Crutzen, 1993]. In addition, NO3 is a strong oxidizing agent and initiates the nighttime degradation of many volatile organic com-Copyright 1996 by the Aanerican Geophysical Union. Paper number 96JD01549. 0148-0227/96/96JD-01549509.00 pounds (VOC), including olefins, terpenes, isoprene, dimethylsulphide (DMS), aromatic hydrocarbons, or organic sulphur compounds [Winer et al., 198•; Atkinson, 1990; Wayne et al., 1991]. Also, the formation of significant concentrations of peroxy radicals (HO2 and higher RO2) during nighttime can be initiated by NO3 reactions, even OH can be produced [Platt et al., 1990; LeBras et al., 1993]. Owing to the addition of NO3 to the C-C double bond of alkenes, and via formation of peroxiacetylnitrate-(PAN) type species a contribution to the formation of organic nitrates is assumed to occur during nighttime [Roberts, 1990; Canttell et al., 1986; Atkinson, 1990; Ridley et al., 1992]. Furthermore, liberation of highly reactive Br-and Cl-containing species from sea salt is possible. In particular, formation of BrNO2 and C1NO2 by reaction of N205 with NaBr or NaC1, ro,qpect, ive!y, cont, a.inod in sea salt aerosol particles is assumed to be of interest [Finla•lson-Pitts et al., 1989; 1990; Behnke et al., 1991; 1993]. Many more details of t...

Direct measurement of NO<sub>3</sub> reactivity in a boreal forest

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Secondary organic aerosol (SOA) formation from reaction of isoprene with nitrate radicals (NO&lt;sub&gt;3&lt;/sub&gt;)

“…After sunset, the isoprene mixing ratio drops rapidly, and it has been suggested that the reaction with nitrate radicals, NO 3 , is a major contributor to isoprene decay at night (Curren et al, 1998;Starn et al, 1998;Stroud et al, 2002;Steinbacher et al, 2005). Typical NO 3 radical mixing ratios in boundary layer continental air masses range between ∼10 to ∼100 ppt (Platt and Janssen, 1995;Smith et al, 1995;Heintz et al, 1996;Carslaw et al, 1997). However, concentrations as high as…”

Direct observations of daytime NO3: Implications for urban boundary layer chemistry

“…Consequently, OH was neglected during the night and NO 3 during the day [e.g., Armerding et al, 1997;Atkinson, 2000;Crosley, 1997;Eisele et al, 1997;Finlayson-Pitts and Pitts, 2000;Fuentes et al, 2000;Kleinman, 2000;Logan et al, 1981;Monks et al, 1998;Platt, 1991;Wayne et al, 1991;Weaver et al, 1996]. In fact, OH and NO 3 measurements were often paused during nighttime and daytime, respectively [e.g., Allan et al, 1999;Brune et al, 1995;Geyer et al, 2001a;Hard et al, 1995;Heintz et al, 1996;Holland et al, 1998;Mount et al, 1997;Platt et al, 1981]. Today it is becoming clear that this separation is not generally valid.…”