Pan Measurements Research Articles

Five years of continuous observations of PAN and ozone at a rural location in eastern Canada

Five years of measurements of PAN and O3 at a rural site in eastern Canada are reported. The measurements were made year‐round and only interrupted due to instrumental failures. The data are analyzed by advanced statistical methods to determine temporal trends, both for PAN and O3 individually and with respect to their covariance. Since the data are clearly lognormally distributed, this analysis is performed on the logarithmic transform of the data. PAN shows a statistically significant long‐term trend but O3 does not. It is argued that this trend may be the result of a change in the overall hydrocarbon composition of the air, since no trend in NOx emissions appears to have taken place over the same time period in eastern North America. Strong seasonal trends in PAN and O3 are found that are similar in overall pattern but differ in detail. The similarity in shape leads to a significant covariance between PAN and O3. The differences in detail can be interpreted as indicative of well‐known atmospheric processes, such as the impact of stratospheric folding occurrences leading to additional O3 with respect to PAN in the spring and reduced photochemical activity and lower temperatures in the winter months, which results in a decoupling of the covariance between O3 and PAN. On a day‐to‐day basis the covariance between PAN and O3 is strong due to the fact that it is essentially determined by meteorological variation. Episodes of alternatively clean and polluted air are observed, each lasting circa 3 days. Seasonal trends in the diurnal patterns are also evident for both compounds: diurnal variation in the summer is considerable but becomes negligible in the winter. PAN displays a larger diurnal variation than O3 in the summer, which can be explained by their relative dry deposition velocities.

Estimating U.S. Class A Pan Evaporation from Few Climate Data

ABSTRACT In view of the shortage of good measurements of lake evaporation for testing a new estimation formula, a modification of the formula has been devised that can be compared with U.S. Class A pan measurements. which are available widely. Both formulae, for lake and pan evaporation respectively, are based on Penman's evaporation equation and are for use when the only reliable data that are available are daily extreme temperatures. for instance. The pan evaporation formula allows for the geometry of a U.S. Class A pan evaporimeter, and for the wetness and albedo of its surroundings, without requiring any empirical calibration based on evaporation measurements. The resulting equation for the monthly mean pan evaporation rate (the so-called ‘Penpan’ formula) includes an estimate of the solar irradiance, which may be obtained from the extra-terrestrial radiation and the cloudiness, derived from rainfall figures. Estimates of evaporation differ from measurements with pans at nine places around the world b...

Summertime partitioning and budget of NOy compounds in the troposphere over Alaska and Canada: ABLE 3B

As part of NASA's Arctic Boundary Layer Expedition 3A and 3B field measurement programs, measurements of NOx, HNO3, PAN, PPN, and NOy were made in the middle to lower troposphere over Alaska and Canada during the summers of 1988 and 1990. These measurements are used to assess the degree of closure within the reactive odd nitrogen (NxOy) budget through the comparison of the values of NOy measured with a catalytic convertor to the sum of individually measured NOy (i) compounds (i.e., ΣNOy (i) = NOx + HNO3 + PAN + PPN). Significant differences were observed between the various study regions. In the lower 6 km of the troposphere over Alaska and the Hudson Bay lowlands of Canada a significant fraction of the NOy budget (30 to 60%) could not be accounted for by the measured ΣNOy (i). This deficit in the NOy budget is about 100 to 200 parts per trillion by volume (pptv) in the lower troposphere (0.15 to 3 km) and about 200 to 400 pptv in the middle free troposphere (3 to 6.2 km). Conversely, the NOy budget in the northern Labrador and Quebec regions of Canada is almost totally accounted for within the combined measurement uncertainties of NOy and the various NOy (i) compounds. A substantial portion of the NOy budget's “missing compounds” appears to be coupled to the photochemical and/or dynamical parameters influencing the tropospheric oxidative potential over these regions. A combination of factors are suggested as the causes for the variability observed in the NOy budget. In addition, the apparent stability of compounds represented by the NOy budget deficit in the lower‐altitude range questions the ability of these compounds to participate as reversible reservoirs for“active”odd nitrogen and suggest that some portion of the NOy budget may consist of relatively unreactive nitrogen‐containing compounds.

Ambient Levels of the Peroxyacyl Nitrates PAN, PPN and MPAN in Atlanta, Georgia

Ambient levels of the peroxyacyl nitrates [RC(O)OONO2] PAN (R = CH3), PPN (R = C2H5-) and MPAN [R = CH2 = C(CH3)-] have been measured in July - August 1992 in downtown Atlanta, Georgia. Ambient levels of PAN reached 2.9 ppb and averaged 0.71 ± 0.53 ppb(n=817). PPN reached 0.37 ppb and averaged 0.14 ±0.14 ppb (n = 119). Diurnal variations of PAN and PPN were similar and included nighttime minimaand late afternoon/early evening maxima. MPAN was observed on only 12 occasions at levels averaging 0.32 ± 0.07 ppb. A brief descriptive analysis of the data is presented together with a documentation of our measurement and calibration protocols and the results of an interlaboratory comparison involving co-located measurements of ambient PAN.

Passive Sampling of Atmospheric Photochemical Oxidants

Abstract A simple, cost-effective passive sampler is described that is suitable for measuring parts per billion (ppb) levels of photochemical oxidants (ozone + nitrogen dioxide + peroxyacetyl nitrate + peroxypropionyl nitrate) in ambient air. The passive sampler makes use of oxidant-fugitive colorants, and color changes are proportional to the oxidant dose, i.e. the product of oxidant concentration and sampling duration. Field tests have been carried out at a southern California mountain forest location with co-located passive samplers and continuous measurements of O3, NO2, PAN and PPN. Consistency with laboratory tests of the color change with oxidants studied singly (O3, NO2, PAN) or as a mixture is discussed. Interferences from formaldehyde and sulfur dioxide are negligible. Four colorants have been tested and yield detection limits ranging from 8 to 54 ppb. day (1-8 ppb. week, and so on).

Determination of the relative ozone and PAN deposition velocities at night

A series of measurements of PAN and ozone was conducted during summer at three rural sites in Canada: Egbert and Dorset, Ontario, and Kejimkujik, Nova Scotia. For nights when a stable surface inversion layer forms, ozone and PAN at the surface are found to undergo first order decay, assumed to be due only to dry deposition. Analysis of the measurement data leads to determination of the relative dry deposition velocities. For all three sites, we find that Vd(O3)/Vd(PAN) = 0.42±0.19, at night. This ratio is roughly a factor of 5–6 times smaller than previously assumed. This smaller relative deposition velocity ratio can have a significant impact on model estimations of PAN concentrations near the surface. We estimate that for these sites, the PAN deposition velocity is at least 0.5 cm/s, and may be greater during daytime. This can have a significant impact on the tropospheric lifetime of PAN.

Real-time Irrigation Scheduling of Cotton with an Automated Pan Evaporation System

High frequency irrigation control necessitates real-time monitoring of soil water, plant water status or atmospheric evaporative demand. The research objective was to determine the suitability of real-time control of subsurface drip irrigation using automated evaporation pan measurements.

Time-averaged measurements of peroxyacetyl nitrate

Time-integrated measurements of PAN have been carried out by sampling ambient air on alkaline alumina cartridges followed by liquid chromatography analysis of acetate with« negative» UV detection (LC-UV). Two cartridges are operated side by side, one at ambient temperature and the other downstream of a thermal converter that decomposes PAN to products other than acetic acid. The first cartridge measures total acetate (PAN + acetic acid), the second measures acetic acid, and PAN is obtained by difference

Measurements of gaseous hydrogen peroxide and PAN in rural southern England

Continuous measurements of gaseous H 2O 2 and PAN made over approximately a 2-year period at a site in rural southern England are reported. The concentrations of both species show diurnal and seasonal trends. PAN and H 2O 2 reached peak concentrations during the afternoon period with the H 2O 2 tending to peak later than the PAN. Seasonal peak concentrations tended to occur in the spring and early summer but photochemical episodes could strongly influence the concentrations of both species. One photochemical episode is examined in detail where the influence of air mass origin is clearly evident. Correlations with ozone during the episode and for the whole data period are given.

One-year measurements of PAN in the Paris basin: Effect of meteorological parameters

PAN has been measured continuously for 1 year in Créteil, a southeastern suburb of Paris Correspondence analysis was used to analyse the important PAN database obtained during this period, in relation to associated meteorological parameters and the location of precursors sources. This analysis revealed a complex relation (U-shaped curve) between PAN and temperatures, with a minimum in the range of 4–12°C and an increase in the lower and higher temperatures, arising from the competition between photochemical production and thermal decomposition. Long-range transport of PAN is associated with easterly winds and occurs under anticyclonic conditions in all seasons, particularly in winter. The highest PAN values (maximum 33.6 ppb) are observed in summer. They have a local origin and are associated with northwesterly to southwesterly winds, revealing the net impact, in summer, of nearby sources such as the urban conglomeration of Paris on PAN levels recorded in the surrounding areas.

Photochemical oxidant concentrations in two Canadian Prairie cities: Model evaluation

It has been previously noted that the cities of Edmonton and Calgary, Alberta (Canada) often act as a sink for ozone, due to removal through reaction with transportation-derived NO, Angle and Sandhu (1989, Atmospheric Environment 23, 215–221). However, an extensive data set of O 3 and PAN measurements for these two cities reveals that occasional oxidant episodes occur. To assess the extent to which these oxidant episodes may be the result of local photochemical oxidant production, a box-model was applied to investigation of oxidant formation during the summer months in Edmonton and Calgary. Using model inputs derived from meteorological data, the measured NO x concentrations, and NMHC NO x ratios that were consistent with observations, computed concentration-time profiles of ozone and PAN for these cities were generated that were similar to the observed profiles. The model used, containing explicit chemistry for selected representative alkanes, alkenes, and aromatics, indicated that oxidant profiles observed during stagnant conditions were consistent with local photochemical production. The potential for downwind formation of ozone and PAN in an urban plume air parcel was also evaluated with the model. It was found that the ozone concentration downwind from the urban source can be significantly elevated and that the presence of an isoprene flux in rural areas can cause significant elevation of PAN concentrations relative to those produced in the city. It is concluded that the combination of a stagnant air mass with urban NMHC and NO x inputs and the solar radiation flux at this latitude (>51°N) can lead to substantial oxidant production near the urban source and elevated concentrations in the rural downwind air mass.

Evaluation of a number of chemical mechanisms for their application in models describing the formation of photochemical ozone in Europe

A series of 24 chemical mechanisms from the literature are compared against each other using harmonized emissions, photolysis rate coefficients for simple inorganic chemistry and life cycle data for ozone, PAN and H 2O 2. The evaluation sought to understand the impact of parameterizing hydrocarbon oxidation on the peak concentrations of photochemically-generated secondary pollutants. Only seven of the 24 chemical mechanisms gave peak concentrations of ozone, PAN and H 2O 2 simultaneously in their respective central ranges. PAN and H 2O 2 were generally calculated with a much lower precision compared to ozone. Only 11 mechanisms out of 24 gave responses to both 50% hydrocarbons and NO x emissions controls in their respective central bands. The lack of coordinated ozone, PAN and hydrogen peroxide measurements across Europe currently limits the adequacy of model comparisons and hence the confidence which may be placed in assessments of likely impacts of future control strategies.

Evaluation for the continent of Australia of the simulation of the surface climate using the Biosphere/Atmosphere Transfer Scheme (BATS) coupled into a global climate model

The Biosphere Atmosphere Transfer Scheme (BATS) of Dickinson et al. (1986) has been coupled to the National Center for Atmospheric Research's Community Climate Model (CCM1). The land surface climatology generated by averaging the results of a 3 yr model integration on a monthly basis is evaluated for the continent of Australia by comparison with published descliptions of a wide range of parameters. The major inconsistencies in the BATS simulahon are associated with surface hydrology: modelled precipitation is too high in the central desert area and the large maxima of rainfall on the coast are grossly underestimated. This may be entirely a result of the coarse resolution of the GCM grid but, since rainfall is of crucial importance to agricultural and water supply activities, the inconsistencies clearly merit further consideration. Further problems associated with the surface hydrological regime include the difficulty of comparing total modelled evapotranspirat~on with evaporation calculated from evaporation pan measurements. In a semi-arid to arid environment such as Australia the latter are gross overestimates. Other differences between the BATS climate and measurements are confined to the central desert area and the crop and short grass regions in the south: simulated maximum temperatures are too high in the desert and minimum temperatures marginally too high in the southeast. Surface net radiation appears to be underestimated in the desert by up to 50 W m-' (probably due to the combined effect of overestimated temperatures and, more importantly, overestimated cloud amounts). Some of these secondary inconsistencies could be partially the result of the poor simulation of surface hydrological regimes which, in turn, seems likely to be primarily the fault of the coarse spatial resolution of the model. Proposals are outlined for improved methods of validation and testing the predictions of such complex biospheric submodels, at least at continental scale.

The relationship between daylight evaporation from short vegetation and the USWB Class A pan

Knowledge of the mechanism of evaporation from a wire mesh-protected USWB Class A pan is imperative for accurately assessing evaporation from reference crop, TEr, and hence atmospheric evaporation demand, AED. An existing mathematical model to calculate evaporation from the A pan was appropriately modified. Micrometeorological measurements were used to explain the mechanism of evaporation from the A pan. The modifications include the calculation of thermal energy storage and the establishment of a wind function for the daylight period. The modified model yielded an index of agreement and mean absolute difference between modelled and measured values of 0.92 and 0.76 mm (28% of mean pan measurements) for the daylight period, respectively. The mean difference was 0.06 mm or 2% of mean pan measurements. This model was used to create functions for transforming pan evaporation to AED. The ratios of estimated TEr to partially transformed pan measurements and untransformed pan measurements were 1.13 and 4.62, respectively, for daylight. The coefficients of variation of 44 observations for the ratio of TEr to partially transformed and untransformed pan measurements were ±36 and ±222%, respectively.

Pan measurements in a forested area (Donon, France)

Abstract Continuous PAN measurements using a fully automated gas chromatograph have been performed since September 1986 in a forested area (Donon) in the east of France. The results showed a marked seasonal variation with a maximum observed in spring. A PAN concentration of 0.2 ppb can be considered as the background level of this region, while substantial PAN levels (1–2 ppb) were recorded during several transport episodes. One of them is analysed and discussed in detail.

The impact of rapid urbanization on pan evaporation in phoenix. Arizona

AbstractRapid urbanization in Phoenix, Arizona over the past few decades has been associated with large increases in local temperature and wind speed values, and decreases in local dew point and relative humidity levels. In this study, the impact of these urban‐induced climatic changes on long‐term pan evaporation rates is identified. The results indicate an increase from 1917 to 1985 in the local pan evaporation in all months of the year. Following a long period of generally increasing pan evaporation levels, a sharp jump in the pan measurements occurred in the late 1960s. This pronounced discontinuity in the long‐term record appears to be associated with the construction of a nearby regional shopping centre in 1968. Given widespread similar land‐use changes throughout this rapidly growing desert city, and given the well‐documented changes in local climatic conditions, potential evapotranspiration increases are probably occurring throughout much of the metropolitan area.

Atmospheric trace gas analysis using matrix isolation-fourier transform infrared spectroscopy

A novel cryogenic sampling method combining the matrix isolation technique with FTIR spectroscopy has been developed for atmospheric trace gas analysis. It is applicable to a wide range of molecules with detection limits typically in the 10–50 ppt range. The method is described along with some measurements of N2O, CFCl3, CF2Cl2, OCS, CS2, SO2 and PAN from samples collected at ground level and from an aircraft between 9 and 14 km.

Measurements of NOY species and O3 at 82° N latitude

Measurements of NO2, HNO3, and PAN, as well as O3 were made in March 1985 at Alert, N.W.T., Canada. The observations show that PAN is by far the dominant NOy species at this Northern location at the onset of spring. Surface loss of HNO3 and possibly O3 seemed to occur over the snowy surface, but no loss of PAN was apparent. The observations are further evidence for the importance of PAN as a major carrier of the oxides of nitrogen in the clean troposphere. Although concurrently measured light hydrocarbons would appear to be sufficient for local formation of PAN, it is suggested that this did not take place but rather that long range transport from more southerly regions was responsible for the observed PAN levels.

Verification of a mathematical model for aerosol nitrate and nitric acid formation and its use for control measure evaluation

A mathematical model for the formation of atmospheric nitric acid and aerosol nitrate has been developed and employed to study the effect of emission controls. Based on a Lagrangian formulation of the atmospheric diffusion equation, the model computes nitric acid concentrations from a description of daytime photochemical reactions and night-time reactions involving NO 3 and N 2O 5. Ammonium nitrate formation is computed at a thermodynamic equilibrium between HNO 3 and NH 3, and heterogeneous reactions between HNO 3 and preexisting aerosol are considered. The accuracy of the air quality model's predictions is verified by comparison to O 3, NO 2, HNO 3, NH 3, aerosol nitrate and PAN measurements made for this purpose in California's South Coast Air Basin during the period of 30–31 August 1982. Examination of emission control alternatives shows that reduction in NO x emissions yields a nearly proportional decrease in total inorganic nitrate levels (HNO 3 + aerosol nitrates). Reduction in NH 3 emissions suppresses aerosol nitrate formation, resulting in higher HNO 3 levels. Control of organic species emissions by the amounts expected in Los Angeles in future years causes a partial shift away from PAN formation toward greater production of HNO 3. Emission control strategies can be formulated that include a combination of controls on NO x organic gases and NH 3 emissions that will achieve a greater reduction in HNO 3, aerosol nitrate and O 3 levels than a strategy predicated on control of only a single precursor species.

Peroxyacetyl nitrate: comparison of alkaline hydrolysis and chemiluminescence methods

Peroxyacetyl nitrate (PAN; CH/sub 3/C(O)OONO/sub 2/) was prepared from sunlight irradiation of organic-NO/sub x/ and chlorine-organic-NO/sub x/ mixtures in air, and its concentration was measured by using two methods. The first method involved ion chromatography following alkaline hydrolysis of PAN to acetate, and the second method involved PAN measurements using a chemiluminescent NO/sub x/ analyzer. The two methods were found to be in good agreement in the range of PAN concentrations tested, 0-400 ppb. Applications and limitations of the two methods are discussed for both laboratory and ambient measurements of PAN.