TILLERING AND LEAF AREA OF WINTER BARLEY EXPOSED TO SULPHUR DIOXIDE IN THE FIELD.

Winter barley (Hordeum vulgare L., cv. 'Igri'), grown as a crop in the field, was exposed to SO2 concentrations ranging from 40 to 200 ppb [parts per billion (109 ) by volume] above ambient. From spring onwards, plants at 40 and 50 ppb were consistently the heaviest, having slightly more tillers than plants in the other plots. In the range 80 to 200 ppb SO2 , the plants usually had fewer tillers than the controls, but this difference was not consistent throughout the season. Trends in the numbers and weights of tillers were interpreted as circumstantial evidence that 80 to 200 ppb of SO2 may have decreased assimilate production. Leaf area in May was markedly bigger in fumigated plants than in the controls. At 80 to 200 ppb the increases may have resulted from the plants having diverted a greater proportion of shoot dry weight into leaf tissue and from increased specific leaf area. These responses of 'Igri' barley in the field resembled those obtained by other workers for the same variety grown in controlled environments.

The influence of open-top chambers on the growth and development of field bean.

In 1988, open-top chambers (OTCs) based on the Raleigh (USA) design were used to investigate the effect of ambient pollutants on field-sown Vicia faba cv, Ticol. This paper reports an aspect of this study in which the effect of the chamber itself on crop growth and development was investigated. Non-filtered chamber (NF OTC) microclimates were typically 0.8°C warmer, with 20% less radiation and reduced wind speeds compared with open-field sub-plots (AA treatments). These differences are sufficient to induce alterations in the growth and development of V. faba. Plant development progressed more quickly inside the chambers in response to the faster accumulation of thermal time. Chamber-grown V. faba were up to 20 cm taller and had fewer branches (0.7 compared with 1.2 per plant) than plants grown in the AA treatments. Larger leaf areas developed on the NF plants, and there were fewer stomata per unit leaf area in this treatment (34 compared with 42 mm-2 , P= 0.01). Enclosure within an OTC did not alter the number of flowers per plant or the number of flowers which formed pods. However, at harvest, chamber-grown plants had a 13% higher yield than the plants grown in open-field plots. These differences in growth are described in relation to the microclimate differences between AA and NF treatments.

Yield stimulation of a commonly grown cultivar of Phaseolus vulgaris L. at near-ambient ozone concentrations.

Seeds of Phaseolus vulgaris L. ev. Nerina were hand-sown inside open-top chambers (OTCs) in which the plants were exposed to charcoal-filtered air (CF treatment), ambient air (NF), or ambient air with added 6, 12, 18, 25 or 30 nl 1-1 of ozone (NF6, NF12, NF18, NF25 and NF30 treatments, respectively). Exposure commenced as the crop emerged and continued on a daily basis until the end of the season. Ozone (O3 ) was added between 10.00 and 18.00 h GMT. The seasonal 7 h mean O3 concentrations ranged from 10 nl l-1 in the CF treatment to 50 nl l-1 in the NF30 treatment. The growth and yield of P. vulgaris ev. Nerina demonstrated two distinct responses to O3 depending upon concentration. At seasonal 7 h means of 20, 26 and 32 nl l-1 (NF, NF6 and NF12 treatments respectively), the yield increased relative to that of the CF treatment. The increase in yield peaked at 48% in the NF6 treatment (P < 0.05), and was associated with a 55 % increase in the maximum leaf number, longer retention of the canopy, and a 45 % increase in the number of pods present at the final harvest. In contrast, seasonal 7 h mean O3 concentrations of 38, 45 and 50 nl l-1 (NF18, NF25 and NF30 treatments) caused 26-42 % reductions in the yield of P. vulgaris. The leaves of such plants developed extensive symptoms of O3 injury and were prematurely abscised from the plants. The reductions in yield were due to a decrease in the numbers of seeds per pod and in the weights of individual seeds.

Some foliar characteristics of ash trees (Fraxinus excelsior) exposed to ozone episodes.

Young ash trees (Fraxinus excelsior L.) growing in the field were exposed to episodes of 150 nl 1-1 ozone, or to clean air, in open-top chambers at the University of Nottingham, Sutton Bonington Campus, UK, May-October, 1992-1994. The episodes were for 8 h daily and for 1-4 d in succession, with seasonal totals of 24-27 d. A nondestructive method for estimating whole-tree leaf area was developed in 1992 and used to monitor leaf area, leaf number and leaf size in 1993 and 1994. Stomatal density and leaf abscission were also studied. No effects of exposure to ozone on leaf area and leaf number were detected. In 1994 there were consistent trends towards greater mean leaf size and higher stomatal density in trees exposed to ozone, but these effects were not significant at the 95% confidence level. Leaf abscission was slower in trees exposed to ozone in 1992 and 1994, but not in 1993 when there were fewer exposure days late in the season.

Measuring and modelling the airborne particulate matter mass concentration field in the street environment: model overview and evaluation.

This paper discusses the outline structure and preliminary evaluation of an emission-dispersion model for predicting the temporal and spatial distribution of vehicle-derived airborne particulate matter mass concentration in street canyons. The model is called Street Level Air Quality (SLAQ). SLAQ is semi-empirical, in that it uses not only results from field and wind tunnel experiments but also theory and models derived from multiple runs of numerical routines in order to simulate the basic physical processes within the street canyon. A combination of a plume model, for the direct contribution of vehicle exhaust, and a box model for the recirculating part of the pollutants in the street, is used to predict concentration for receptors within the canyon. Emission rates of vehicle-derived particulate matter are calculated within SLAQ, which serve as input to the dispersion module. Exhaust emission rates are scaled element by element along the street for each of the lanes according to the direction of traffic flow to account for modal operation of vehicles near signalised intersections. This refinement allows SLAQ to account for non-uniformity in along-canyon emission rates and to model a street that has several intersections along its length. Thermal turbulence due to environmental surface sensible heat and vehicle-generated heat is accounted for in the model. Other features of SLAQ include correction for the urban heat island effect, dry deposition, wet deposition, particle settling and estimation of wind direction standard deviation, when this latter data is not available. SLAQ has been evaluated in a street in Loughborough, Leicestershire, United Kingdom and correlation coefficient of 0.8 between the modelled and measured concentrations has been obtained.

Measured and modelled concentrations and vertical profiles of airborne particulate matter within the boundary layer of a street canyon.

Concentrations and vertical profiles of various fractions of airborne particulate matter (suspended particulate matter (SPM), PM10 and PM2.5) have been measured over the first three metres from ground in a street canyon. Measurements were carried out using automated near real-time apparatus called the Kinetic Sequential Sampling (KSS) system. KSS system is essentially an electronically-controlled lift carrying a real-time particle monitor for sampling air sequentially, at different heights within the breathing zone, which includes all heights within the surface layer of a street canyon at which people may breathe. Data is automatically logged at the different receptor levels, for the determination of the average vertical concentration profile of airborne particulate matter. For measuring the airborne particle concentration, a Grimm Dust Monitor 1.104/5 was used. The recorded data also allows for time series analysis of airborne particulate matter concentration at different heights. Time series data and hourly-average vertical concentration profiles in the boundary layer of the confines of a street are thought to be mainly determined by traffic emissions and traffic associated processes. Hence the measured data were compared with results of a street canyon emission-dispersion model in time and space. This Street Level Air Quality (SLAQ) model employs the plume-box technique and includes modules for simulating vehicle-generated effects such as thermally- and mechanically-generated turbulence and resuspension of road dust. Environmental processes, such as turbulence resulting from surface sensible heat and the formation of sulphate aerosol from sulphur dioxide exhaust emissions, are taken into account. The paper presents an outline description of the measuring technique and model used, and a comparison of the measured and modelled data.

Indoor and outdoor measurements of vertical concentration profiles of airborne particulate matter.

Vertical concentration profiles of various particle size ranges of airborne particulate matter were measured from ground level up to 3 m, in outdoor and indoor environments. Indoor measurements were carried out in an electronics workshop, while two outdoor environments were chosen: a street canyon cutting across a town and an open field situated in a semi-rural environment. The novel measurement technique employed in this experimental work, which can also be used to determine vertical concentration gradients of pollutants other than airborne particles in different environments, is given particular attention. Analyses of the collected data for the environments considered are presented and some conclusions and plausible explanations of the profiles are discussed. The workshop and street canyon environments exhibited larger concentrations and vertical concentration gradients as compared to the sports field. This indicates that people breathing at different heights are subjected to different concentrations of airborne particulate matter, which has implications for sitting air pollution monitors intended for protection of public health and estimation of human exposure.

Effects of elevated carbon dioxide and ozone on the growth and yield of potatoes (Solanum tuberosum) grown in open-top chambers.

Potato (Solanum tuberosum cv. Bintje) was grown in open-top chambers under three carbon dioxide (ambient and seasonal mean concentrations of 550 and 680 mumol mol-1 CO2) and two ozone concentrations (ambient and an 8 h day-1 seasonal mean of 50 nmol mol-1 O3) between emergence and final harvest. Periodic non-destructive measurements were made and destructive harvests were carried out at three key developmental stages (24, 49 and 101 days after emergence) to establish effects on growth and tuber yield. Season-long exposure to elevated O3 reduced above-ground dry weight at final harvest by 8.4% (P < 0.05), but did not affect tuber yields. There was no significant interaction between CO2 and O3 for any of the growth and yield variables examined. Non-destructive analyses revealed no significant effect of elevated CO2 on plant height, leaf number or green leaf area ratio. However, destructive harvests at tuber initiation and 500 degrees Cd after emergence showed that above-ground dry weight (8 and 7% respectively) and tuber yield (88 and 44%) were significantly increased (P < 0.05) in the 550 mumol mol-1 CO2 treatment. Responses to 550 and 680 mumol mol-1 CO2 were not significantly different for most parameters examined, suggesting the existence of an upper limit to the beneficial influence of CO2 enrichment. Significant effects on above-ground dry weight and tuber yield were no longer apparent at final harvest, although tuber numbers were increased (P < 0.05) under elevated CO2, particularly in the smaller size categories. The results show that the O3 treatment imposed was insufficient to reduce tuber yields and that, although elevated CO2 enhanced crop growth during the early stages of the season, this beneficial effect was not sustained to maturity.

Development and preliminary evaluation of a particulate matter emission factor model for European motor vehicles.

Although modeling of gaseous emissions from motor vehicles is now quite advanced, prediction of particulate emissions is still at an unsophisticated stage. Emission factors for gasoline vehicles are not reliably available, since gasoline vehicles are not included in the European Union (EU) emission test procedure. Regarding diesel vehicles, emission factors are available for different driving cycles but give little information about change of emissions with speed or engine load. We have developed size-specific speed-dependent emission factors for gasoline and diesel vehicles. Other vehicle-generated emission factors are also considered and the empirical equation for re-entrained road dust is modified to include humidity effects. A methodology is proposed to calculate modal (accelerating, cruising, or idling) emission factors. The emission factors cover particle size ranges up to 10 microns, either from published data or from user-defined size distributions. A particulate matter emission factor model (PMFAC), which incorporates virtually all the available information on particulate emissions for European motor vehicles, has been developed. PMFAC calculates the emission factors for five particle size ranges [i.e., total suspended particulates (TSP), PM10, PM5, PM2.5, and PM1] from both vehicle exhaust and nonexhaust emissions, such as tire wear, brake wear, and re-entrained road dust. The model can be used for an unlimited number of roads and lanes, and to calculate emission factors near an intersection in user-defined elements of the lane. PMFAC can be used for a variety of fleet structures. Hot emission factors at the user-defined speed can be calculated for individual vehicles, along with relative cold-to-hot emission factors. The model accounts for the proportions of distance driven with cold engines as a function of ambient temperature and road type (i.e., urban, rural, or motorway). A preliminary evaluation of PMFAC with an available dispersion model to predict the airborne concentration in the urban environment is presented. The trial was on the A6 trunk road where it passes through Loughborough, a medium-size town in the English East Midlands. This evaluation for TSP and PM10 was carried out for a range of traffic fleet compositions, speeds, and meteorological conditions. Given the limited basis of the evaluation, encouraging agreement was shown between predicted and measured concentrations.

Kinetic sequential sampling (KSS) system: an automated sampling system for measuring vertical concentration profiles of airborne particles.

An electronically controlled lift system carrying a real-time particle monitor has been developed for sampling air sequentially, at different heights within the breathing zone. Data are automatically logged at the different receptor levels, for the determination of average vertical concentration profiles of airborne particulate matter. The system is easy to operate, portable, and easily extended to different heights or modified for use with other types of monitors (e.g., a portable CO analyzer). For measuring airborne particle concentrations, a Grimm Dust Monitor 1.104/5 was used. The results of trial runs, which were carried out indoors and in a relatively open semi-rural area, are presented, and applications of the kinetic sequential sampling (KSS) system are discussed.

Predicting wheat yields: the search for valid and precise models.

Interest in predicting wheat yield in terms of physiological, cultural and meteorological variables is more than a century old. Early attempts involved statistical analyses of relationships between yield and observational data on precipitation, temperature, radiation, etc., and scientific study of physiological and cultural influences such as dates of sowing or anthesis, farming procedures and soil treatments. More recently these have been augmented by large-scale mechanistic models of phenological development, such as AFRCWHEAT, CERES and SIRIUS, incorporating some simulation facilities. All approaches implicitly involve fitting models of some sort: statistical, mechanistic or (preferably) a hybrid of these forms. Levels of success on this important matter are highly variable. After reviewing the field, we consider the results of recent efforts to contrast and evaluate the (large-scale) mechanistic approaches, using spatial/temporal methods for interpolating the required climatological input variables. The work employs a substantial database of wheat yields assembled for this purpose. After assessing the validity of the large-scale mechanistic models (with some intriguing conclusions), we then consider some results from a current approach to parsimonious hybrid modelling, based on statistical study of accessible climatological data interpreted in terms of physiological knowledge of key influences on plant development.