Cloud Measurement (Aerosol filter measurement)

1. Cloud Measurement (Aerosol filter measurement) Colorado State University, Atmospheric Science Jeffrey L. Collett and Taehyoung Lee

2. Hi-Volume Sampler (Aerosol) Filter holders Filter Pump 2.5 µm TSP Flow Recorder • Large flowrate (~1000 LPM) allowing for collection of large amount of mass • Size cut : either TSP (Total suspend particle) or 2.5 µm

3. Instruments (Cloud) • Volumetric flow rate : 19m3/min • The Large Dp50 (the front fraction) : 17 – 18 µm • The small Dp50 (the rear fraction) : 4 µm • Sampling time : typically 1 – 2 hrs • 20 bin resolution (Range 2- 50 µm) • Sampling frequency : 0.1 to 10 Hz • Sampling flow : 1 m3/min • Computation and real-time display : Median volume diameter(MVD), Equivalent diameter (ED), and liquid water content (LWC) • Real-time display: • Integrated Particle Surface Area (PSA), and Integrated Particle Volume (LWC) • Size range : 3 – 45 µm • Sample flow : 3 cm3/min

4. Introduction (Cloud drops) • Drops form by condensation on particles • Soluble gases partition to drop • Scavenged particles and gases determine initial drop composition ; Reactions modify composition Figure taken from “cloud chemistry” by Jeffrey Collett

5. What are we looking for in collected cloud drops? The collected cloud water samples are immediately analyzed for pH and aliquotted to preserve unstable species Active Cloud water collector • pH (on-site measurement) • H2O2 • HCHO • Major Ions (Cl-, NO3-, SO42-, Na+, NH4+, K+, Ca2+ and Mg2+) • S(IV) • Metal • Organic acid (Carboxylic acid) • TOC (Total Organic Carbon) • LC/MS (Organic nitrogen and sulfur)? PVM /FM-100 • Liquid water content • Drop size distribution

6. How to preserve chemical species we are looking for? • Major ions and TOC No additional preserved sol. required (Ion Chromatography and TOC analyzer) • H2O2 Adding p-hydroxyphenylacetic acid (POPHA) to form a stable dimer (Spectrofluorophotometer) • S(IV) Adding catalase sol. To destroy any H2O2 Adding formaldehyde to form stable hydroxymethanesulfonate (HMS) (VIS/UV spectrophotometer) • Metal (Fe and Mn) Adding Nitric acid to prevent metal adsorption on wall in vial (Atomic Absorption Spectrophotometer) • Organic Acid Adding Chloroform to prevent biological consumption (Ion Chromatography) • HCHO Adding bisulfite sol. to form stable HMS (Spectrofluorophotometer)

7. FM-100 Higher pH in large drops  faster oxidation • competing reaction under mass transport limited conditions • Understanding African Dust influence on cloud drop size distribution • Understanding drop size distribution changes influence on cloud pH and chemical composition

8. S(IV) oxidation pathway influence Cloud Measurements pH, H2O2 and Metal (Fe and Mn) Other Science Groups Gaseous SO2 Gaseous O3 • Sulfate is produced by aqueous phase • SO2 oxidation • Obtaining critical information about • the relative importance and rates of • aqueous s(IV) oxidation by 3 oxidation • pathways

9. Cloud chemical composition influence Cloud Measurements Major ions, Total Organic Carbon, Organic Acids Other Science Groups aerosol-time-flight mass spectrometry (ATOFMS) • Understanding aerosol-cloud interaction • Particle types scavenged by cloud drops • Cloud-processed aerosol properties • Understanding African Dust influence • on cloud composition • Any information of secondary organic aerosol • (SOA) Mean ionic composition of DYCOMS-II Cloud water (Straub et al, JGR(2007))