“NITRIC/OXALIC/NITROUS ACID” AEROSOLS Thomas Townsend and John R

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INVESTIGATIONS OF THE HETEROGENEOUS REACTIONS BETWEEN AMMONIA AND “NITRIC/OXALIC/NITROUS ACID” AEROSOLS Thomas Townsend and John R. Sodeau. Centre for Research into Atmospheric Chemistry, Department of Chemistry, University College Cork and Environmental Research Institute, Cork, Ireland. INTRODUCTION Nitric acid is mainly produced from the Oxalic acid is produced from biomass REDUCES following two reactions, the NOx burning, vehicle emissions and biogenic ENVIRONMENTAL precursors formed as a result of lightning ACIDIFICATION activity. The aerosols formed from and combustion processes. condensation and nucleation play an important role in cloud formation and NO + OH· → HNO Day 2 3 their radiative properties. N O + H O → 2HNO Night 2 5 2 3 AMMONIA AIM OF THIS WORK ENHANCES Effects of particles: PARTICLE The purpose of the research is to elucidate the FORMATION Health implications when inhaled interactions between ammonia with nitric/nitrous acid Nitrous acid (HONO) is a source of the KEY ROLE IN Reduce and distort visibility aerosols over a range of concentrations and humidities. · NITRATE/SULFATE hydroxyl radical (OH ) one of the key species in Oxalic acid was also introduced and its effects PARTITIONING Climate change photochemical cycles for ozone production and established by comparing FTIR spectra, [NH ]+ 4 smog. Formation occurs on surfaces in the Provide surfaces for “new” reactions production and size of the particles. presence of water and NOx. INSTRUMENTATION AMMONIA RESULTS (100ppm standard, AEROSOL GENERATION Diffusion dryer Ammonium 0.25%wt HNO3 + HNO3/HNO2/C2H2O4 aerosol Dilution Unit NH3/N2) diluted to ppb range. Admitted to flow Nitrate or 300ccm NH3 generated by passing a flow of HNO 300ccm NH 0.75%wt C2H2O4 air over a heated solution or tube via a 6mm diameter Nitrate ion 3 3 90%RH P via a nebuliser. movable, glass injector. 60%RH AEROSOL FLOW-REACTOR 0.5%wt HNO3 + C2H2O4 AerosolAerosol Humidifier Made of glass, ID: 10cm, maximal Generator RELATIVE HUMIDITY reactive length Z: 80cm. (RH) tuned between 1% and 95%. Aerosol Flow Carrier Flow Operated at room temperature and Comp. Air atmospheric pressure. Unit Flow concentration: 2L/mn. Nitrogen PARTICLE SIZER (SMPS) HNO3 300ccm NH3 Flow velocity 1cm/s. Dioxide 0.75%wt HNO3 + Monitors aerosol fraction, 20%RH NH3/N2 0.25%wt C2H2O4 particle size, mass, surface SMPS CHEMILUMINESCENCE area, volume. TSI 3081 NH NOx Monitor. Catalytic 3 Analyser + oxidation of NH3/NH4 to NO.

FTIR Digilab FTS 3000 MCT FTIR Catalytic Size distributions when heating Nitric Acid NO,NO2 levels for nitric and oxalic acid Converter 3 using an MCT detector 1.80E+07 0.5%w t nitric acid + 0.75%w t oxalic acid and BaF windows: 2 Denuder 1.60E+07 90%RH 0.75%w t nitric acid + 0.25%w t oxalic acid monitors both gas and RH 2.5 + DENUDER Coated with 0.25%w t nitric acid + 0.75%w t oxalic acid aerosol condensed phase. Aerosol sampling To NH3/NH4 sampling 1.40E+07 Exhaust oxalic acid, removes NH3(g).

3 1.20E+07 300ccm NH 2 3 1.00E+07

8.00E+06 ppm

2 1.5

EQUATIONS/STRUCTURES conc. dN#/cm 6.00E+06 NO,NO 4.00E+06 1

4HNO3(g)(heated) → 4NO2(g) + 2H2O(g) + O2(g) 2.00E+06 0.5 0.00E+00 Ammonium Oxalate 10 Diameter (nm) 100 1000 Nitrogen Dioxide Cis HNO3 20%RH HNO3 90%RH + 0 NH4 - + HNO3 + 100ccm NH3 90%RH HNO3 + 200ccm NH3 O O H O HNO3 + 300ccm NH3 0 50 100 150 200 250 O N O 3 Course of experiment (min) . N O H C C H+

NH - Size Distributions for different aerosol concentrations at 50%RH and O 3 O O + 0.5%wt HCl + Nitrous acid NH4 300ccm NH3 added - 300ccm NH3 90%RH + ------NH4 O 4.00E+07 2.50E+05 - 0.5%wt NaNO2 0.5%/0.5% wt. nitric acid/oxalic acid + O O O H3O O H 0.75%/0.25% wt. nitric acid/oxalic acid 0.25%/0.75% wt. nitric acid/oxalic acid N 3.50E+07 N C C O N 2.00E+05 + 3.00E+07 O O H O Trans O 2.50E+07 Ammonium Nitrate Organonitrate? O 1.50E+05

2.00E+07

1.00E+05 HCl(aq) + NaNO2(aq)→ HONO (?) + NaCl(aq) conc.d#/cm-3 1.50E+07

1.00E+07 5.00E+04

5.00E+06 300ccm NH 10%RH 3 0.00E+00 0.00E+00 DISCUSSION 0 20 40 60 80 100 120 Diameter (nm) FTIR: On heating HNO3, it was found that NO2 was present, whereas - at high humidities and using the nebuliser, NO3 absorptions appeared. It -1 + -1 -1 is unclear whether the 1400cm peak is an NH4 or nitrate absorption. Wavenumber(cm ) Assigned Component Wavenumber(cm ) Assigned Component

Nitric and Oxalic acid aerosols gave spectra with characteristic + 1724 -1653 NO2 asymmetric stretch 1443 NH4 deformation carboxylic absorptions and nitrate peaks. 1678 -1633 NO stretch (HONO) 1378 -1211 NO symmetric stretch A likely cis/trans structure of HONO has been produced and complex 2 formation with ammonia or water is possible. 1593 CO stretching 1310 CO-/COH stretching

NOx Monitor: NOx data could not be analysed accurately due to + 1458 -1382 NOH bend (nitrate) 1294 -1265 NOH bend (HONO) competition between NO/NO2 gas from nitric/nitrous acid and [NH4] .

NO2 levels were at first particularly high, however these lowered and consequentially the [NO] increased as %RH and NH were added. 3 CONCLUSION FUTURE WORK SMPS: Few particles were observed initially for heated HNO3 but more FTIR spectra produced nitrate, gaseous NO2, Vary the interaction times of ammonia 6-7 (10 ,130-160nm) emerged as humidity and ammonia increased. oxalate, ammonium, HONO absorptions with with the aerosols to calculate kinetic concentration and humidity being a factor in For nitric/oxalic acid, bimodal size distributions were recorded measurements and uptake coefficients. appearance of spectra. suggesting different particles . Smaller amounts of larger particles Investigate the interactions between (0.75%wt oxalic) implies more incorporation of water and ammonia. Sizes of the particles correlated NH3, H2SO4 and other dicarboxylic well with changing composition e.g. addition acids such as malonic and succinic acid. of oxalic acid or ammonia. ACKNOWLEDGEMENTS!: I would like to thank the following funding institutions for supporting this research, as well as the CRAC lab crew!