Showing papers by "Roy M. Harrison published in 2000"

Characterization of Particles from a Current Technology Heavy-Duty Diesel Engine

Abstract: The physical properties, chemical properties, and morphology of particles from a current technology diesel engine run under steady-state conditions were determined during five campaigns across three calendar years. Concentrations of particulate matter, NOx, HC, CO, and CO2 measured at a fixed sampling position were found to be repeatable between different campaigns. However, particle size distributions and number concentrations were significantly affected by dilution conditions. Particle density, estimated using a volume size distribution estimated from an ELPI together with measured mass, was found to be below 1 g/cm3 at nonzero loads, but this is explained by an overestimation of volume by the ELPI due to particle fractal properties. Particle phase SO42-, NO3-, PAH, organic carbon, and elemental carbon were found to vary with engine operating modes. Particles emitted from a modern diesel engine had similar cluster structures to those from old engines but consisted of smaller basic particles when analyze...

Measurement of number, mass and size distribution of particles in the atmosphere

Abstract: Typical size distributions for airborne particles are described and the significance of the ultrafine fraction highlighted. Size distributions may be expressed in terms of either mass (volume), surface area or number, and the interpretation of each is discussed together with appropriate measurement methods. The sources of ultrafine particles in the atmosphere include both primary emissions and secondary particles formed through homogeneous nucleation processes within the atmosphere. Examples of measurements of atmospheric ultrafine particles are given, highlighting situations with high concentrations of primary ultrafine particles and also situations where gas–to–particle conversion through homogeneous nucleation gives rise to bursts of new particle production. Finally, the relationship between particle mass and number within the atmosphere at a polluted site is examined.

ACE-2 HILLCLOUD. An overview of the ACE-2 ground-based cloud experiment

Abstract: The ACE‐2 HILLCLOUD experiment was carried out on the island of Tenerife in June–July 1997 to investigate the interaction of the boundary layer aerosol with a hill cap cloud forming over a ridge to the north‐east of the island. The cloud was used as a natural flow through reactor to investigate the dependence of the cloud microphysics and chemistry on the characteristics of the aerosols and trace gases entering cloud, and to simultaneously study the influence of the physical and chemical processes occurring within the cloud on the size distribution, chemical and hygroscopic properties of the aerosol exiting cloud. 5 major ground base sites were used, measuring trace gases and aerosols upwind and downwind of the cloud, and cloud microphysics and chemistry and interstitial aerosol and gases within the cloud on the hill. 8 intensive measurement periods or runs were undertaken during cloud events, (nocturnally for seven of the eight runs) and were carried out in a wide range of airmass conditions from clean maritime to polluted continental. Polluted air was characterised by higher than average concentrations of ozone (>50 ppbv), fine and accumulation mode aerosols (>3000 and >1500 cm−3, respectively) and higher aerosol mass loadings. Cloud droplet number concentrations N, increased from 50 cm−3 in background maritime air to >2500 cm−3 in aged polluted continental air, a concentration much higher than had previously been detected. Surprisingly, N was seen to vary almost linearly with aerosol number across this range. The droplet aerosol analyser (DAA) measured higher droplet numbers than the corrected forward scattering spectrometer probe (FSSP) in the most polluted air, but at other times there was good agreement (FSSP=0.95 DAA with an r2=0.89 for N<1200 cm−3). Background ammonia gas concentrations were around 0.3 ppbv even in air originating over the ocean, another unexpected but important result for the region. NO2 was present in background concentrations of typically 15 pptv to 100 pptv and NO˙3 (the nitrate radical) was observed at night throughout. Calculations suggest NO˙3 losses were mainly by reaction with DMS to produce nitric acid. Low concentrations of SO2(∼30 pptv), HNO3 and HCl were always present. HNO3 concentrations were higher in polluted episodes and calculations implied that these exceeded those which could be accounted for by NO2 oxidation. It is presumed that nitric and hydrochloric acids were present as a result of outgassing from aerosol, the HNO3 from nitrate rich aerosol transported into the region from upwind of Tenerife, and HCl from sea salt aerosol newly formed at the sea surface. The oxidants hydrogen peroxide and ozone were abundant (i.e., were well in excess over SO2 throughout the experiment). Occasions of significant aerosol growth following cloud processing were observed, particularly in cleaner cases. Observations and modelling suggested this was due mainly to the take up of nitric acid, hydrochloric acid and ammonia by the smallest activated aerosol particles. On a few occasions a small contribution was made by the in‐cloud oxidation of S(IV). The implications of these results from HILLCLOUD for the climatologically more important stratocumulus Marine Boundary Layer (MBL) clouds are considered.

Observations of new particle production in the atmosphere of a moderately polluted site in eastern England

Abstract: Measurements of particle number density and Fuchs surface area, together with a range of gaseous pollutant concentrations, have been made in June 1995 at a coastal site in eastern England which receives air from a range of polluted and less polluted origins. Periods of enhanced local particle production were identified and found to be associated predominantly with relatively polluted air sectors. An examination of the factors contributing to homogeneous nucleation and hence new particle production suggests that those most important at this location are probably the production of hydroxyl radicals and the availability of ammonia. A numerical modeling study calculating characteristic timescales for new particle production and for condensation onto existing aerosol surfaces is able to predict periods of new particle production. The model suggests that oxidation of dimethyl sulphide and sulphur dioxide and homogeneous nucleation of sulphuric acid and water, probably in combination with ammonia, are the source of new particles at this site.

Quasi‐Lagrangian investigation into dimethyl sulfide oxidation in maritime air using a combination of measurements and model

Abstract: Using a combination of field measurement data and a modified photochemical box model, strong evidence is presented to suggest that the rate of daytime oxidation of dimethyl sulfide (DMS) by OH radicals is insufficient to describe the measured conversion. Quasi-Lagrangian measurements were made at two sites in the eastern Atlantic (Research Vessel and Mace Head Research Station, Ireland) as part of the Atmospheric Chemistry Studies in the Oceanic Environment (ACSOE) program. Periods of connected flow between the two sites were identified, air parcel transit times were estimated, and measurements of the main DMS oxidation products (MSA, SO2, and nss-SO4 2−) were compared with model predictions to establish whether the model's chemical mechanism could account for observed changes. The main finding was that during daytime periods with maritime air masses, the model failed to predict a sufficient increase in DMS oxidation products during the estimated transit time. This was despite a tendency to overprediction of the progress of nitrogen chemistry during air mass advection, and independent checks on the model estimates of hydroxyl radical concentrations through measurements. In the light of this, the involvement of halogen species (most probably halogen oxides) or heterogeneous oxidation processes is tentatively suggested as the cause of enhanced daytime DMS oxidation in the marine boundary layer (MBL). Increasing the rate constant for the OH + DMS reaction by a factor of 3.3 (as a crude way of simulating parallel channels of DMS oxidation) permitted model results to reproduce the measurements very much more closely.

Causes and environmental implications of increased UV-B radiation

Abstract: Stratospheric ozone depletion: a discussion of our present understanding Ozone depletion and changes in environmental UV-B radiation Marine photochemistry and UV radiation Assessing biological and chemical effects of UV in the marine environment: Spectral weighting functions Effects of solar UV-B radiation on terrestrial biota Sunlight, skin cancer and ozone depletion.

Marine and land‐based influences on atmospheric ammonia and ammonium over Tenerife

Abstract: Concentrations of gaseous ammonia ([NH 3 ]) and aerosol ammonium ([NH 4 + ]) were measured across Tenerife as part of the ACE-2 “HILLCLOUD” experiment to assess the effect of cloud processing on the marine budget of reduced nitrogen (NH x ) Several methods for measuring NH 3 were applied: continuous rotating annular denuder, diffusion scrubber and multi-stage filter packs, with the latter also measuring NH 4 + The measurement sites were located both upwind and downwind of the hill-cloud Terrestrial NH 3 sources provide a major constraint in addressing marine NH x from land-based studies, and the measurements showed local NH 3 emissions from both decomposing potato fields and livestock [NH 3 ] was correlated between upwind and downwind sites; at high [NH 3 ](>05 μg m -3 ) values were larger downwind than upwind, indicating the importance of island sources In contrast, at high [NH 4 + ](>05 μg m -3 ), [NH 4 + ] was significantly smaller downwind than upwind, while at low [NH 4 + ](02μg m -3 ), the opposite was observed The decrease in [NH 4 + ] suggests that cloud processing in high [NH 4 + ] conditions may enhance the evaporation of NH 3 from NH 4 + in cloud, while NH 4 + aerosol formation could occur at low [NH 4 + ] Analysis of the average diurnal variability in [NH 3 ] and [NH 4 + ] at the different sites suggests that both NH 3 emissions and post-cloud evaporation of NH 4 + to NH 3 are largest during the day, coupled with increased temperatures and reduced relative humidities Although the marine NH 4 + aerosol is mostly present as non-volatile ammonium sulphate, evaporation of NH 4 + at high [NH 4 + ] may be explained by in-cloud mixing with nitrate and chloride leading to the production of NH 4 NO3 and NH 4 Cl which are subsequently volatilized on leaving the cloud DOI: 101034/j1600-0889200000042x

Chemistry in the marine environment

Abstract: Chemistry in the marine environment , Chemistry in the marine environment , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Impact of correcting peak flow for nonlinear errors on air pollutant effect estimates from a panel study

Abstract: Air pollutant effects are commonly investigated using panel studies employing daily measurement of changes in peak expiratory flow (PEF). Variable orifice PEF meters are inaccurate with a nonlinear relationship to actual PEF. The impact on a panel study of correcting these errors was examined. Twice-daily PEF readings were taken by 147 9-yr old children for 8 weeks and corrected using an equation derived from the response of 32 Vitalograph meters to a servomechanism-controlled pump. Pollutant effect estimates for corrected and uncorrected readings were derived using a regression approach incorporating appropriate confounders. Correction impacted little on mean PEF values (333.1-334.2 L x min(-1)), but did alter effect sizes. Nonsignificant nitrogen dioxide estimates for the entire panel decreased by up to 73%, but, for symptomatic/atopic children, a significant 5-day mean result was lost (decrease in effect size from -2.53 to -0.90% per 10 parts per billion (ppb)) and lag 0 became significant (decrease from -0.51 to -1.22% per 10 ppb). Mass concentration estimates of particles with a 50% cut-off aerodynamic diameter of 2.5 microm moved in both directions (-0.22 changed to 0.11% per 10 microg x m(-1) lag 3 and -0.29 to -0.73% per 10 microg x m(-3) for the 5-day mean). Correction of nonlinearity of peak expiratory flow meters influenced the overall outcome of this panel study, and the changes in effect estimates would be sufficient to alter the interpretation of some studies. For adults, a greater change in effect estimates may follow the larger correction required for their usual peak expiratory flow range.

Research Project for Observation and Modelling of Urban Air Pollution in Uk West Midlands

Abstract: The project, Pollution of the Urban Midlands Atmosphere (PUMA), is funded by Natural Environment Research Council (NERC) of the UK through a thematic programme on Urban Regeneration and the Environment (URGENT), which aims at a better understanding of natural processes in the shallow sub-surface, urban ecology, hydrological balances and atmospheric dynamics and chemistry in urban environments.

Chemical Transformations in the North Sea Atmosphere

Abstract: The work described has focused on a number of inter-related areas, mostly concerned with the chemistry of nitrogen compoundsin the marine atmosphere. Initially, concentrations of various individual nitrogen compounds were determined over the North Sea. The averaging of data from many individual cruises permitted the mapping of average concentrations across the southern bight of the North Sea. These measurements were used to infer chemical transformations of nitrogen compounds, particularly the dissociation of ammonium nitrate aerosol and the reaction of nitric acid with sodium chloride particles and to calculate atmospheric nitrogen inputs to the North Sea. The measurements of gaseous ammonia in the North Sea atmosphere were combined with data from ammonium in seawater made during the same series of cruises to estimate surface exchange of ammonia. The work showed that the North Sea system is rather finally balanced with respect to ammonia, with the majority of net fluxes from air-to-sea, but some periods when the sea becomes a net source of ammonia in air. In a Lagrangian experiment, concentrations of a number of gaseous and particulate nitrogen species were measured on two ships located 200 km apart. The data have been used to evaluate the rate of oxidation of nitrogen dioxide in the North Sea atmosphere and to estimate concentrations of the hydroxyl radical in daytime, and to evaluate the mechanism of the night-time oxidation of NO2. In a variant upon this experiment, neutralisation of aerosol acidity arriving at the English coast in ammonia-depleted North Sea air was followed as the air was adverted in ammonia-rich air over eastern England. A pseudo first rate order rate constant for the loss of aerosol H+ was estimated and found to vary with the degree of neutralisation of the aerosol. In a numerical modelling study collaborative with the Danish National Environmental Research Institute, the North Sea measurement data were compared with the predictions of airborne concentrations from the Danish Eulerian model with non-linear chemistry. After some modifications to the chemical scheme in the model, it was found that model predictions were in extremely good agreement with measured concentrations.