Heinz-Ulrich Krüger

Formation of atomic ci from sea spray via photolysis ofnitryl chloride: determination of the sticking coefficient of N205 on NaCl aerosol

Abstract The sticking coefficient of N205 on NaCl aerosol is determined in a smog chamber (in an inserted teflon bag) at 292 K, and the rate constant for the consecutive chemical reaction leading to formation of ClNO2 is determined at various relative humidities between 71 and 92%. A preliminary evaluation of these first experiments indicates that the sticking coefficient increases with increasing humidity from 0.024 to 0.05 in that range, whereas the portion leading to CINO2 decreases from 0.61 to 0.3.

Formation of ClNO2 and HONO in the presence of NO2, O3 and wet NaCl aerosol

Abstract The sticking coefficient of N 2 O 5 on NaCl aerosol α =0.032±0.003 is determined at 292.3±0.5K and various relative humidities, considering the decrease of the aerosol diameter during the reaction. The rate constant ratio for the consecutive chemical reaction leading to ClNO 2 (a) or 2 HNO 3 (b) is determined to be k a / k b =2.5±0.7. For a solution of 18 weight percent NaCl and pH values above 2 the ratio is independent of pH and decreases for low pH.

Atmospheric degradation of a semivolatile aerosol-borne pesticide: Reaction of OH with pyrifenox (an Oxime-Ether), adsorbed on SiO2

The reactivity of both isomers (Z and E) of pyrifenox (2′,4′-dichloro-2-(3-pyridyl)acetophenone (E,Z)O-methyloxime), adsorbed on quartz-aerosol as an inert carrier, against OH radicals from the gas-phase was investigated in a smog chamber (2400 l) at T=299 K and 50% rel. humidity. OH-radicals were produced in the dark using hydrazine/ozone and peroxynitric acid/NO and by photolysis using methyl nitrite, hydrogen peroxide, ozone and nitrogen dioxide as OH-precursors. OH-radical concentrations (< 105 < [OH]/cm−3 < 8 · 106) were determined from the simultaneous consumption of up to 6 reference compounds with well-known OH-rate constants. Using methyl nitrite, nitrogen dioxide and peroxynitric acid as OH-precursors the OH-rate constant at T=299 K for pyrifenox was found to be identical for both isomers: (kOH ± σ) = (1.8 ± 0.4)·10−11cm3·s−1 leading to half-lives of pyrifenox in the atmosphere of t12 = (0.45 – 0.9) days at typical mean, tropospheric OH-radical concentrations in the range of [OH] = (5 – 10) · 105 cm−3. Side reactions of HO2 or other radicals perturbed the degradation behaviour of pyrifenox in the presence of hydrazine/ozone and hydrogen peroxide and ozone under irradiation and were separated from OH. The rate constants for the reaction with gaseous hydrogen peroxide and ozone were determined, found to be low and negligible with respect to the degradation of pyrifenox in the environment: (kO3 ± σ) = (2 ± 1) · 10−19 cm3 s−1 and (kH2O2 ± σ) = (8 ± 8) · 10−20 cm3 s−1. Besides the reaction with OH-radicals a photo- isomerization Z ⇌ E was found. Within the error of experiments no irreversible loss of pyrifenox due to photolysis was found. A ketone (after reaction of OH at the CH2-group in pyrifenox) was tentatively assigned as the only product found.

Time resolved Infrared Spectroscopy of Formation and Processing of Secondary Organic Aerosols

Abstract An aerosol flow reactor was coupled to an infrared absorption cell to study aerosol formation processes with high temporal resolution. The recorded infrared spectra were referenced using aerosol smog chamber experiments. Evaluation was done by studying the formation of secondary organic aerosol from α-pinene and catechol as precursors and ozone as oxidant. Three main infrared absorptions: ν(O-H), ν(C-H) and ν(C=O) were considered, and humic like properties of the secondary organic aerosol are mainly interpreted according to the formation and variations of carbonyl bands in the region between 1850 and 1600 cm−1, especially the ν(C=O) of aryl carbonyls from catechol oxidation products below 1700 cm−1. The relative intensities of two major ν(C=O) stretching vibrations at 1690 cm−1 and 1755 cm−1 were observed to depend strongly on the available ozone concentration. At high precursor/ozone ratios (2:1 or 1:1) the vibration at 1690 cm−1 predominates, indicating aryl carbonyl vibrations. With increasing ozone concentrations this vibration is replaced by the higher carbonyl vibration at 1755 cm−1 indicating unsaturated carbonyl-containing compounds. This is a strong hint at ring opening processes leading to unsaturated aliphatic compounds in the resulting particle. Aryl carbonyls and aromatic or olefinic ν(C=C) at 1620 cm−1 in aged particles remain visible, as aerosol smog chamber studies exhibit – thus a strong hint at humic like properties of the SOA from the spectroscopic point of view.

Direct Deposition of Aerosol Particles on an ATR Crystal for FTIR Spectroscopy Using an Electrostatic Precipitator

An electrostatic precipitator (ESP) has been developed for collecting aerosol samples for attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) from an aerosol chamber. The ESP deposits the aerosol particles directly onto the ATR crystal with high efficiency. The ESP-ATR spectra are observed to agree well with the spectrum of a filter sample, transferred by impression. ZnSe ATR crystals have been found most suitable for electrostatic precipitation due to surface hardness, transmission characteristics and deposition behavior. ESP-ATR-FTIR spectroscopy might be a powerful tool not only for in situ but also for online measurements of aerosols.

Circular multireflection cell for optical spectroscopy.

We constructed a circular multireflection (CMR) cell, allowing multireflection around the center of the cell. This is caused by a skewed adjustment of the entering beam (equivalent to a simple parallel shift/offset), avoiding the center of the cell, thus leading to multiple reflections. The experimental setup with a cell with an inner diameter of 6 cm showed up to 17.5 beam passes on polished aluminum and attained path lengths up to 105 cm, demonstrated by Fourier transform infrared measurements of CO(2) gas between 2283 and 2400 cm(-1). The circular concept, i.e., the centering of the reflections, is useful for absorption spectroscopy on trace gases and aerosols. The optical alignment of the cell can completely be performed from outside the experimental setup, e.g., an aerosol flow reactor or a vacuum system. The variation of the path length is easily possible by adjusting the position of the cell with respect to the entering light beam.