AQUEOUS PHOTOCHEMISTRY: One focus of our research will be on determining the extent to which the organic nitrogen observed in canopy throughfall rainwater at UMBS [Hill et al., 2005] may be formed through aqueous phase photochemical reactions, on the canopy surfaces. Recent measurements imply that a significant amount of organic nitrates are formed by reactions with peroxy radicals derived from photochemical degradation of organic matter in solution, but this has yet to be confirmed or quantified. We propose to assess the role peroxy radicals play in organic nitrate formation in aqueous systems, including cloud water, rain and dew, collected in the UMBS environment. 1. CLOUD WATER We will study organic nitrate production in cloud water collected using the Airborne Laboratory for Atmospheric Research (ALAR; http://www.chem.purdue.edu/shepson/alar.html). The ALAR platform is a twin engine Beechcraft Duchess, piloted by Dr. Paul Shepson. A modified Mohen slotted rod cloud water collector [Mohnen, 1980; Huebert et al., 1988] is mounted on top of the ALAR [Hill et al., 2007]. The cloud water collector consists of five Teflon rods that direct collected droplets through Teflon tubes into sterilized HDPE bottles. The collection bottles are frozen during collection by cooling with dry ice to ensure that no post collection transformation occurs. This system has been successfully used by multiple members of the Shepson group for cloud water collection [Hill et al., 2007]. The organic nitrate production in collected cloud water will be studied in the Shepson laboratory. Samples will be irradiated by a solar simulator in a small volume, temperature controlled photochemical reactor. The irradiated samples will subsequently be analyzed by the instrumentation described in section 4. 2. RAIN WATER Our interest in the chemical processing of nitrogen in rain water has been stimulated by the work of Dr. Kimberly Hill. During her 2005 field study at UMBS she found that a significant fraction of the nitrogen in rain water is organic [Hill et al., 2005]. Furthermore, the fraction of the organic nitrogen in canopy throughfall was measured to be higher than in that of the incoming precipitation. Similar to the field campaign of Dr. Hill, rain water samples from above and below the forest canopy will be collected using dry ice cooled HDPE collection bottles and will remain frozen until the time of analysis. Samples will be analyzed before and after irradiation, looking specifically for photochemical production of organic nitrates. Selected throughfall rainwater samples will be analyzed for organic matter by Desorption Electrospray Ionization mass spectrometry (DESI-MS) to examine the impact large molecular weight organic species have in sequestering nitrogen through RONO2 formation. 3. DEW It has been previously established that leaf stomata can uptake gas phase atmospheric organic nitrogen to be incorporated into amino acids [Lockwood et al., 2008]. However, the aqueous phase production and subsequent leaf uptake of organic nitrates in dew has not been studied. Dew water samples will be collected pre and post sunrise as well as after incremental durations on leaf surfaces. We will also create and subsequently collect artificial dew samples by adding distilled water and water with dilute HNO3 to leaf surfaces. These samples will be collected and stored for transport to Purdue similar to the rain water described above. Once at Purdue samples will be irradiated for study of organic nitrate production. We will also conduct GC/MS and DESI-MS analysis of selected samples to examine the nature of organic matter present in the dew. This work will be integrated with continuing year-round laboratory studies at Purdue using these samples. 4. 5. AQUEOUS PHASE SAMPLE ANALYSIS All aqueous phase samples collected will be analyzed using a Purge and Trap GC/ECD. Each sample will be allowed to defrost to room temperature where the RONO2 components will be converted to the gas phase in an Encon Purge and Trap. The Purge and Trap works by having a water sample injected into a fitted glass sparging vessel which is then purged with helium gas. The helium gas carries the purged organic volatiles through a moisture reduction trap to a solid sorbent trap, which retains the organic volatiles until heated. Once heated under helium flow the organic volatiles are desorbed from the chemical trap and injected to the gas chromatograph. For the non-volatile RONO2 species, we will use direct injection analysis and/or organic phase extraction. The gas chromatograph is a Finnigan MAT GC-Q with a Rtx-624 polar column that is designed for volatile organic nitrate separations (Restek Chromatography). The sample is injected from the purge and trap into the temperature controlled column and compounds detected using a Valco pulsed discharge electron capture detector (PDECD). In the detector, the 3% xenon-helium carrier gas is ionization in a discharge, which results in a standing current that is decreased by the presence of electron-capturing compounds such as organic nitrates. To monitor the change in current (change in concentration of compounds), a LabVIEW data acquisition and peak integration program will be implemented. This collected data is then compared to previously collected standards. 4. SOIL FOREST FLOOR RAINFALL SAMPLES Soil samples were obtained using a stainless steel soil corer to a depth of 30 cm, transferred to pre‐labeled, clean, polyethylene bags and homogenized by hand. Forest floor samples were collected by removing the surface litter and cutting 25 × 25 cm squares down to the base of the organic horizon, approximately 5 to 8 cm in depth. Both forest floor samples and soil cores were collected a minimum of 48 hours after rain events. To investigate the impact of rain water on soil NO3− fractionation, 30 cm soil cores were collected both immediately and 20 hrs after the completion of a rain event. All samples collected were frozen at −4 °C until extracted for analysis. Prior to extraction, all soil samples were sieved and any visible roots, rocks, and insects were removed. Homogenized soil cores were sub‐sampled in 50 g aliquots, extracted with 60 mL nano‐pure water (to remove the nitrate in soil solution), and underwent 0.22 mm filtration. Rain and cloud water samples were weighed and filtered using the same system. Samples were analyzed with an analytical ion chromatograph (Dionex Corporation, Sunnyvale, CA), using an AS‐11 Ion-Pac column and an ED40 electrochemical detector, to determine nitrate concentrations. All samples that had NO3− concentrations below the minimum size required for isotope ratio mass spectrometry (IRMS, 100 nmols in 10 mL) analysis were preconcentrated using a technique detailed in the auxiliary material. Once at the desired concentration, samples were analyzed with a Finnigan Delta Plus Advantage isotope ratio mass spectrometer (Thermo Fischer Scientific,Waltham, MA) using the bacterial reduction and thermal decomposition method described by Casciottietal. [2002] and Kaiser et al. [2007]. Briefly, aqueous samples undergo bacterial reduction using a strain of Pseudomonas aureofaciens to convert aqueous phase NO3− to gas phase nitrous oxide (N2O). TheN2O is thermally converted to O2 and N2 by reduction over a Au surface at 800°C. The O2 and N2 were separated using a 5A molecular sieve gas chromatograph and analyzed by continuous flow isotope ratiomass spectrometry. 5. DESORPTION ELECTROSPRAY IONIZATION (DESI) MASS SPECTROMETRY SAMPLE ANALYSIS To determine the presence, nature and concentration of organic matter in collected samples DESI MS will be used. DESI is an ambient ionization technique that allows for surface analysis to be conducted with no sample preparation. This methodology allows for rapid sample analysis while maintaining stable ionization capabilities. During ionization a solution of 50:50 methanol:water is sprayed onto the surface of interest. The impact of incident droplets results in desorption of surface analytes. These droplets then undergo rapid evaporation leading to free ion production. The ionized species are subsequently studied by mass spectrometry [Costa and Cooks, 2008]. We will apply the technique to both dew and througfall samples, and also to whole leaf samples. 6. STABLE ISOTOPIC ANALYSIS OF OXYGEN IN SOIL AND RAINFALL NITRATE A major objective of this work is to determine the fraction of soil nitrogen that derives from the atmosphere. Isotope ratio mass spectrometry (IRMS) will be used to determine the source of nitrate in soil samples below the canopy. This technique can be used because oxygen has naturally occurring isotopes whose abundance ratios indicate its source, as described above. We will determine the fraction of soil nitrate that is derived from the atmosphere through measurement of d17O in precipitation and in soils. Isotopic analysis (d17O, d18O, d15N) will be determined in nitrate from soils, runoff, precipitation, and through fall. Soil samples, obtained from beneath the canopy, will be collected in HDPE bottles and shipped back to Purdue along with the collected aqueous samples. There nitrate will be extracted, purified and analyzed on a Thermo Delta V isotope ratio mass spectrometer using the bacterial reduction method described by Kaiser et al. [2006]. Briefly, aqueous samples are converted to N2O by bacterial reduction, which is converted to O2 and N2 by reactions over gold at 800°C. The O2 and N2 are separated by GC and analyzed by continuous flow isotope ratio mass spectrometry. This analysis will be done at the Purdue Stable Isotope (PSI) facility (http://www.purdue.edu/eas/psi/) in collaboration with Dr. Greg Michalski.