Kurt Anlauf

Correlation of ozone with NOy in photochemically aged air

During the summer of 1988, measurements of photochemical trace species were made at a coordinated network of seven rural sites in the eastern United States and Canada. At six of these sites concurrent measurements of ozone and the sum of the reactive nitrogen species, NOy, were made, and at four of the sites a measure for the reaction products of the NOx oxidation was obtained. Common to all sites, ozone, in photochemically aged air during the summer, shows an increase with increasing NOy levels, from a background value of 30–40 parts per billion by volume (ppbv) at NOy mixing ratios below 1 ppbv to values between 70 to 100 ppbv at NOy levels of 10 ppbv. Ozone correlates even more closely with the products of the NOx oxidation. The correlations from the different sites agree closely at mixing ratios of the oxidation products below 5 ppbv, but systematic differences appear at higher levels. Variations in the biogenic hydrocarbon emissions may explain these differences.

Nocturnal cleansing flows in a tributary valley

Abstract During photochemical air pollution episodes in the Lower Fraser Valley (LFV) near Vancouver, BC, daytime upvalley flows carried polluted air, with high ozone (0 3 ) concentrations, into tributary valleys to the north of the LFV. Nighttime flows out of the valleys had low 0 3 concentrations, according to surface measurements, and also had low aerosol concentrations, as measured by a scanning Doppler lidar. Analysis of lidar scan data showed that the flows were highly complex, that the relatively clean flow was confined to the lower levels (lowest ∼ 500 m) of the valley, and that regions of strongest outflow were also the regions of “cleanest” air. Measurements of NO 2 concentrations well above background levels in the outflow indicate that it was formerly polluted air from which 0 3 and aerosols had been removed. Possible removal mechanisms were found to be dry deposition in the katabatic (downslope) flows down the valley sidewalls, in agreement with a previous study in a Swiss valley, or fast chemical reactions with NO and N0 3 . Nearly horizontal lidar scans showed that the valley exit flows penetrated into the LFV, where they merged with the downvalley/land-breeze system along the Fraser River.

Relationships between PAN and Ozone at sites in Eastern North America

Measurements of ozone and PAN (peroxyacetic nitric anhydride) were made at four sites in eastern North America; Bondville, Illinois, Egbert, Ontario, Scotia, Pennsylvania, and Whitetop Mountain, Virginia., in July and August of 1988 as part of a study of regional oxidant photochemistry. The concentrations of PAN ranged from <0.010 to 9.2 parts-per-billion by volume (ppbv) and those of 03 ranged from <2 to 139 ppbv. Diurnal concentration profiles showed PAN and 03 to be removed within nocturnal boundary layers, especially if nitric oxide was present, and that 03 was, for most sites, more rapidly removed than PAN. The only mountain top site at which PAN was measured showed distinctly different diurnal profiles in which 03 was actually higher at night, suggesting that convective flow driven by surface cooling served to transport air down from higher in the mixed layer at night. The afternoon production of PAN and 03 was also apparent and led to an overall linear correlation of 03 and PAN between the hours of 1300 and 1800. The comparison of this result with other measurements, estimates of PAN formation rates, and model calculations indicates that the production of PAN relative to ozone is far greater (x3) than can be accounted for by acetaldehyde reactions with OH, there is a wide disparity in model descriptions of PAN production, and confirms the non-linear dependence of 03 production on NOx.

Halogen Atom Concentrations in the Arctic Troposphere Derived from Hydrocarbon Measurements: Impact on the Budget of Formaldehyde

As part of the Polar Sunrise Experiment in 1998 measurements of hydrocarbons were made at the Canadian Arctic station Alert. Halogen atom concentrations play a key role in determining formaldehyde mixing ratios. Formalde- hyde mixing ratios observed during ozone depletion episodes agree with those calculated from time integrated halogen atom concentrations. Formaldehyde is the most important loss mechanism for active bromine and at the same time an im- portant source for HOx radicals. Via these reactions formal- dehyde will indirectly influence chlorine chemistry and thus feedback mechanisms involving halogen atom concentrations and formaldehyde are likely to play a major role in the development of tropospheric ozone depletion episodes during polar sunrise.

Polar sunrise experiment 1995: Hydrocarbon measurements and tropospheric Cl and Br-atoms chemistry

Abstract As part of the Polar Sunrise Experiments (PSE) 1995, we report our results on measurement of non-methane hydrocarbons (NMHC) collected at Alert, Northwest Territories, Canada (82.5° N, 62.3° W) from Julian days 57 to 113, 1995 along with our data on continuous methane and ozone measurements during the same period. The concentration of NMHCs such as alkanes correlated well with that of methane during the dark period before polar sunrise. However, no correlation was observed after the sunrise. Several ozone depletion events and concurrent decreases in hydrocarbon concentrations relative to their background levels were observed. In all ozone depletion periods, concentration changes of alkanes and toluene were consistent with the occurrence of Cl-atom reactions. The characteristics of alkane isomer concentration changes suggest the dominance of HO chemistry prior to, and a switch to Cl chemistry after, the polar sunrise (during the ozone depletion events). The changes in ethyne concentration from their background level were in excess of those expected from Cl-atom kinetics alone and are attributed to additional Br-atom reactions. The time integral for Br mixing ratios is a few orders of magnitudes higher than that for Cl-atoms, suggesting much higher Br-atom concentrations compared to Cl-atom concentrations, if they are present simultaneously.

Discussion of a lagrangian trajectory model describing long-range transport of oxides of nitrogen, the incorporation of pan in the chemical mechanism, and supporting measurements of pan and nitrate species at rural sites in Ontario, Canada

Abstract The derivation of a highly simplified parameterization of NO x chemistry for use with the AES Lagrangian trajectory model is described. Two versions, both employing essentially independent first-order kinetics are discussed: 1. (1) a one step mechanism: NO 2 → inorganic nitrate and 2. (2) a somewhat more involved reaction scheme including PAN chemistry. Evaluation of model performance is attempted with data from the Canadian Air and Precipitation Monitoring Network (APN). It is shown that both model versions are able to reproduce trends of annual and monthly average atmospheric nitrate concentrations, although the models tend to suggest transport over larger distances than is apparent from the field data. The inclusion of PAN chemistry appears to improve the model performance. However, the model predicts a winter maximum and a summer minimum for the annual profile of PAN, and this is in direct contradiction with field measurements of PAN elsewhere. Initial results from a PAN measurement program conducted at three sites in Ontario are also reported and compared with the second model version. Observations for summer 1982 are predicted quite well, but data collected during March 1983 are substantially overpredicted. It is indicated that during periods of rain, PAN constitutes the major oxidized NO x component. The suggestion is made that this observation is due to a much more efficient precipitation scavenging of nitrate species than of PAN.

Summer aerosol profiles over Algonquin Park, Canada

Abstract During the summer of 1982, daytime vertical profiles of aerosol particle concentrations and state parameters in the lower troposphere were measured from a Twin Otter aircraft flying over Algonquin Park, Canada. Particles from 0.2 to 30 μm diameter were counted and sized with PMS ASASP and FSSP wingmounted probes. When 48-h back trajectories at 850 mb were from the south, the mean aerosol particle concentrations were approximately 2000cm−3 at 950mb (near ground level), and decreased with height rapidly until 750 mb. When trajectories were from the west and north, the 950 mb concentrations were much lower but relatively uniform to 800 mb. Individual profiles showed that maxima could occur near cloud base. Average number, area and volume spectra of the subμm aerosol have been determined for 700 and 900 mb and show a maximum near 0.2–0.3 μm with volume-weighted geometric mean diameters near 0.3 μm. Spectra of particles larger than 2 μm indicate a second maximum at about 10 μm diameter. Ground-based chemistry measurements show that most of the subμm aerosol particles of southern origin were formed principally from water soluble sulphate compounds. Based on the measurements made during southerly winds, radiation calculations predict visibilities of appproximately 10 km and suggest that particle absorption could result in a 2–4°C temperature increase in the atmospheric layer below 2 km.

Non-methane hydrocarbons and CO during PACIFIC '93

Abstract Measurements of hydrocarbons and CO that were made during the summer of 1993 as part of the PACIFIC 93 field study in the Lower Fraser Valley, B.C., Canada are summarized. Good comparison between diverse data sets is observed. It appears that on basis of percent carbon (by weight) alkanes (excluding ethane) represent about 55%, alkenes 10%, aromatics (excluding benzene) 20%, and the biogenic hydrocarbon isoprene 3% of the total mass. Classification schemes that incorporate the different reactivity of the compounds suggest much less importance of the alkanes in favor of the alkenes and aromatics. About 10% of ozone production seems to be due to isoprene chemistry alone. Ozone is shown to increase during the day most likely due to photochemistry involving these hydrocarbons. Using hydrocarbon data from a location downwind of the city of Vancouver, and maximum ozone reactivity (MOR) factors derived by Carter (1991, EPA Report, 84pp.) it is estimated that the O3 production rate in the first week of August 1993 might have been as high as 8 ppbv h−1.

Estimating primary and secondary production of HCHO in eastern North America based on gas phase measurements and principal component analysis

Based on atmospheric measurements of multiple species at Egbert, a rural site in Ontario, Canada, during summer 1988, the emission ratios of HCHO/CO and HCHO/ΣNOy for area sources and secondary production of HCHO have been estimated using a modified principal component analysis technique. The technique yields three principal components that represent a photochemically aged air mass, a diurnal cycle, and fresh area emissions. The area emission component has an emission ratio CO/ΣNOy = 9±3 and SO2/CO = 0.005±0.003, in agreement with NAPAP area emission data for the eastern US [Buhr et al., 1992]. The emission ratios of HCHO/CO and HCHO/ΣNOy in this component are 0.0056±0.0022 and 0.05±0.007, respectively. If these ratios are typical of eastern North American area emissions, the total primary HCHO emission for this region will be 8×109 moles HCHO annually based on the NAPAP CO emission inventories. Evidence of secondary HCHO production can be found in the photochemically aged component which has considerably higher HCHO/CO (0.016±0.004) and HCHO/ΣNOy (0.29±0.03) ratios than the emission ratios. It is estimated that for every 1 ppb NOx converted to NOy, 0.4 ppb HCHO are produced for the ratio (1−NOx/NOy)<0.6; after which the relative HCHO production rate becomes smaller. Using this relative rate, the maximum total HCHO production over the eastern North America is estimated to be 1.3×1011 moles year−1, or approximately 16 times that from primary emission.

Daytime Photochemical Pollutant Transport over a Tributary Valley Lake in Southwestern British Columbia

Abstract Tethersonde, lidar, aircraft, and surface chemistry measurements from an intensive field campaign (Pacific’93) in the Lower Fraser Valley (LFV) demonstrate the daytime advection of pollutants into a lake-filled valley adjoining a broad urbanized coastal valley. On three separate days (immediately before, during, and after a pollutant episode), elevated concentrations of ozone (O3) in the narrow tributary valley could be attributed to the advection of pollutants northward from sources in the LFV (primarily metropolitan Vancouver). On 5 August, the highest concentrations of O3 observed in the region during the entire episode were observed over the tributary lake. Simple Lagrangian mass budget calculations suggest that the unusually high concentrations observed on 5 August over the lake were physically reasonable and consistent with the known chemistry of the air advected into the valley. They also indicate that reductions in O3 flux divergence during the overlake trajectory in the Pitt Valley, prim...