INVESTIGATIONS OF THE HETEROGENEOUS REACTION BETWEEN AMMONIA AND SULFURIC/SULFUROUS ACID AEROSOLS Thomas Townsend, Colette Noonan and John R. Sodeau Centre for Research into Atmospheric Chemistry, Department of Chemistry, University College Cork, and Environmental Research Institute, Cork, Ireland. [email protected] INTRODUCTION EXPERIMENTAL SET-UP AMMONIA (100ppm Sulfuric acid aerosol is formed by the oxidation of SO in standard, NH /N ) diluted to 2 RELATIVE HUMIDITY (RH) 3 2 gas/aqueous/aerosol phase. The preferred form of sulfuric acid tuned between 1% and 70%. ppb range. Admitted to flow AEROSOL GENERATION tube via a 6mm diameter in the aerosol phase is ammonium sulfate (NH4)2SO4. If there H2SO4 /C2H2O4 aerosol Dilution Unit movable, glass injector. is not enough ammonia present, sulfuric acid exists either as generated by passing a flow (200-500 ccm) of air over a P H2SO4(aq) or NH4HSO4. heated solution or via a nebuliser. AEROSOL FLOW-REACTOR Aerosols AerosolAerosol Humidifier Generator Made of glass, ID: 10cm, maximal ….are tiny particles suspended in the air. Those larger than reactive length Z: 80cm. Aerosol Flow Carrier Flow Operated at room temperature and Soluble trace gases such as Ammonia, about 1μm in size are mainly produced by windblown dust Comp. Air atmospheric pressure. NH3, are produced from agricultural and sea-spray. Aerosols smaller than 1μm are mostly formed Unit by condensation processes e.g. conversion of SO gas released PARTICLE SIZER (SMPS) sources and represents a significant 2 from volcanic eruptions to sulfate-type particles. Monitors aerosol fraction, NH3/N2 atmospheric pollutant in Ireland. particle size, mass, surface SMPS CHEMILUMINESCENCE area, volume. TSI 3081 NH NOx Monitor. Catalytic 3 Effects of particles: Analyser oxidation of NH /NH + to NO. 3 4 Health implications when inhaled FTIR MCT Catalytic SMPS Converter Reduce and distort visibility FTIR Digilab FTS 3000 Denuder using an MCT detector RH + Climate change Aerosol sampling To NH3/NH4 sampling and BaF2 windows: Exhaust monitors both gas and DENUDER Coated with Provide surfaces for “new” catalytic chemical reactions aerosol condensed phase. oxalic acid, removes NH3(g) Sulfurous acid (H2SO3) has never been characterized or isolated on AIM OF THIS WORK The aim of this work was to investigate Earth. This is caused by the unfavourable conditions for the hydration the interaction of ammonia with sulfuric and sulfurous acid aerosols. The product of SO2 (the first step of its oxidation) within the atmosphere. H2SO4 system was initially studied followed by the H2SO3 counterpart. A Such conditions (high temperature, water content and oxidation), relationship was attempted to be established by comparing the size of these however, can be found on the Jupiter moons Io and Europa. particles, FTIR spectra and ammonium production. RESULTS: H2SO4 System RESULTS: H2SO3 System Various stages of a typical experiment (500ccm H SO at 30%RH) 2 4 SMPS data for 1%wt H2SO3 at different humidities 1.60E+06 H SO 15%RH 1.60E+06 H2SO4 WET: 35%rh 2 3 1.40E+06 1.40E+06 ) 1.20E+06 3 ) 1.20E+06 3 1.00E+06 1.00E+06 8.00E+05 8.00E+05 6.00E+05 6.00E+05 Conc.(dN#/cm 4.00E+05 conc. (dn #/cm 4.00E+05 2.00E+05 2.00E+05 DRY: 1.5%rh 0.00E+00 10 100 1000 0.00E+00 Diameter (nm) 1 Particle diameter (nm) 10 100 Dry H2SO4 Wet H2SO4 100ccm ammonia 200ccm ammonia 300ccm ammonia 11.3% RH 22.4% RH 38.1% RH 48.2% RH 54.4% RH 1.2 + NH3 vs. [NH4 ] @ various [H2SO4] (2%RH) Size Distributions of 4%wt H2SO3 under various conditions 3.50E+06 H2SO3 + NH3 55%RH 1 500cc H2SO4 Low H2SO4; NH3 WET: 35%rh NO Monitor 3.00E+06 0.8 x 400cc H2SO4 2.50E+06 ]ppm 0.6 + 4 300cc H2SO4 2.00E+06 [NH 0.4 200cc H2SO4 1.50E+06 0.2 Conc. (dN #cm3) 1.00E+06 0 DRY: 1.5%rh 0 50 100 150 200 250 300 350 5.00E+05 [NH3] ccm 0.00E+00 Increasing flows of H2SO4 with 200ccm of NH3 at 30%RH O 10 Particle Diameter (nm) 100 1000 6.00E+04 FTIR WET: 35%rh HO S 2.50E+05 H2SO3 (14.6% RH) H2SO3 (32.3% RH) O S O + H2O H2SO3 + 100ccm NH3 (40.3% RH) H2SO3 + 300ccm NH3(42.3%Sulf uRH)r Dioxide 5.00E+04 OH 2.00E+05 Sulfurous Acid (H2SO3) 4.00E+04 High H2SO4; 1.50E+05 NH 3.00E+04 3 OHSO2 1.00E+05 + HSO3 2.00E+04 NH4 O Conc. (dN#/cm3) - H 500ccm H2SO4 only O S H O 1.00E+04 5.00E+04 NH3 H - S DRY: 1.5%rh pH O O S H 0.00E+00 0.00E+00 7 - 12 O O + pH O Diameter (nm) NH4 O 10 100 1000 2 - 7 200ccm 300ccm 400ccm 500ccm Ammonium Sulfite Bisulfite Hydrogen Sulfonate DISCUSSION CONCLUSION FTIR 10 Our investigations into the reaction between -1 NH and H SO aerosols, have shown that the Wet/dry H2SO4 yields the same dissociation products, bisulfate ion at 1180, 1035 and 890cm . 3 2 4 main products formed were, NH4HSO4 and At low [H2SO4] the major “dry” particle is (NH4)2SO4/H2SO4.Varying the humidity yields the (NH4)2SO4/H2SO4/H2O particle. (NH4)2SO4. Their relative importance -1 At higher [H2SO4], ammonium bisulfate is formed as seen from the FTIR both wet and dry. NH3(g) is visible at 966cm depended on both flow concentration and -1 Sulfurous acid produces SO2 in three different phases in the 1350cm region; aqueous, liquid and gas. humidity. -1 -1 -1 Bisulfite isomers (1200cm and 1030cm ) and sulfite (950cm ) are observed on introduction of NH3. Studies into sulfurous acid have shown NOx Monitor typical sulfur dioxide absorptions in + + Low [H2SO4], increase of NH3 does not affect the [NH4 ]. High [H2SO4], [NH4 ] increases proportionally with increase in NH3.. different phases. On addition of ammonia, 2- + bisulfite isomers and SO were observed at The „acidic‟ bisulfate hydrogen is responsible for increased formation of [NH4 ]. 3 + high humidities. An increase of about 0.1ppm [NH4] occurs to H2SO3 at 1%wt on addition of NH3. This may be due to the formation of - - ammonium sulfite which favours alkaline conditions as opposed to the HSO3 /OHSO2 isomers (bisulfite and hydrogen sulfonate). FUTURE WORK SMPS Vary the interaction times, probe mechanistic and kinetic details. NH4HSO4 particle diameter: 70nm; (NH4)2SO4 particle diameter: 200nm. Bimodal distributions are seen for 400ccm [H2SO4]. Humidity and ammonia introduction results in larger sized but smaller numbers of particles for the sulfuric acid system. Investigate the interactions between NH3, H SO , H SO and other organics such as Humidity appears to increase the amount of particles for H2SO3, increased [NH3] results in smaller particle number with larger 2 4 2 3 diameters suggesting more extensive incorporation of ammonia into these acidic aerosols. malonic and succinic acid. ACKNOWLEDGEMENTS!: We would like to thank the following funding institutions for supporting this research, as well as the CRAC lab crew!.