The results of spatial and temporal distribution of volatile organic compounds (VOCs) in ambient air surrounding the Hsinchu Science-Based Industrial Park (SBIP), Taiwan during February 2001 to November 2001 are presented. The sampling was performed at 13 different sites around the SBIP for 24 hrs once every month, and a total of 130 samples were collected. The effects of geographical and meteorological conditions and production volume of the SBIP on the variation of pollutant’s concentration were investigated. The spatial distribution shows that a comparatively higher concentration of VOCs was found at the sites, which are in the southwestern part of SBIP, downwind of or close to factories. When the wind velocity was low (i.e. below 2 m/s), the concentration of pollutant tended to increase and became uniformly distributed around the science park. The temporal distribution shows a decrease in ambient concentration of pollutants from February to June 2001, mainly due to the decline in the production volume of the SBIP in this period. During the whole period of investigation, the concentration of most of the compounds (except acetone and IPA) was found to be lower than the factory-surrounding air quality standard of Taiwan, but in some cases it was higher than the AALG (ambient air level goal).

Surface measurements of the atmospheric electric field, conductivity, and the concentration and size distribution of submicron aerosols were made at Maitri, Antarctica, during the summer Indian Antarctic Expedition of 1996–1997. The main results obtained from these observations are summarized below: The classical concept of the global electric circuit is not validated from the diurnal variation curves of the atmospheric electric field observed during this period. The value of electrical conductivity at the ground surface does not show much diurnal variation. Aerosol size distributions at Maitri are generally trimodal and remain almost similar for several hours or even days in the absence of any meteorological disturbance. Total aerosol concentration increases by approximately an order of magnitude whenever a low-pressure system passes over the station. Observations of aerosols and conductivity made during the onward and return journeys of the cruise strongly support the transport of aerosol and trace gases with the seasonal northeasterly winds from the Indian subcontinent to the Indian Ocean. From the differences observed in latitudinal variation in aerosols and conductivity along the cruise route, one can conclude that the downward transport of the nucleation mode particles from the free troposphere to the marine boundary layer significantly contributes to the nucleation mode particle high concentrations observed up to ITCZ. Changes in the values of conductivity during two episodes of warm and cold fog are studied. Observations are interpreted in terms of ion-attachment and new particle generation processes.

The aim of this report is to document and summarize the results obtained in our wind tunnel experiments for a variety of phenomenon which need to be accounted in our understanding of the interactions of cloud electrification with its microphysics. The vertical wind tunnel developed at IITM has proved to be a good facility to investigate several critical problems in cloud microphysics. Several experiments conducted over last more than three decades in this wind tunnel provided some novel observations and large photographic data captured using a High Speed Camera on the deformation, oscillation, evaporation and breakup characteristics of charged/uncharged water drops of different sizes in absence/ presence of electric fields. However, in order to fill up the gap between the past studies mostly conducted under vertical configuration of electric field, main focus in our experiments was to study the effect of horizontal electric field (EH) on various microphysical processes in thunderclouds. This work has been extended by performing experiments on breakup of polluted and unpolluted water drops in electric field. The data has revealed some novel features of various microphysical processes occurring inside the thunderclouds.

In-situ observations of cloud microphysical properties, carried out over different parts of Indian sub-continent using an instrumented research aircraft during Phase-I of Cloud Aerosol Interaction and Precipitation Enhancement EXperiment (CAIPEEX) from June to September 2009, were studied. Different cloud probes were used to characterize the hydrometeor and precipitation types in the monsoon clouds. The results revealed that all liquid phase hydrometeors were present at temperatures -12 degrees C to 15 degrees C. Most of the presence of rain drops were found in the liquid water content (LWC) range from 0.5 to 2g/m(3). In general, rain drops are initiated when the droplet effective radius (R-e) exceeded 12 mu m. Rain dominated at the tops of young growing convective clouds even at temperatures colder than -10 degrees C. Mixed phase hydrometeors were present at temperatures from -2 degrees C to -18 degrees C. The cases where mixed phase precipitation occurred at temperatures warmer than about -7 degrees C were associated with influx of transported dust aerosol at the upper (supercooled) region of these cloud systems. Ice only hydrometeors were found at temperatures extending from -10 degrees C to -22 degrees C. Most of the monsoon rain is produced by warm and cold cloud/mixed-phase processes in the cloud. The combined R-e. from two different cloud probes is useful for validation of satellite derived cloud microphysical parameter.

Intra-seasonal and inter-annual variability of Bowen Ratio (BR) have been studied over the rain-shadow region of north peninsular India during summer monsoon season. Daily grid point data of latent heat flux (LHF), sensible heat flux (SHF) from NCEP/NCAR Reanalysis for the period 1970–2014 have been used to compute daily area-mean BR. Daily grid point rainfall data at a resolution of 0.25° × 0.25° from APHRODITE’s Water Resources for the available period 1970–2007 have been used to study the association between rainfall and BR. The study revealed that BR rapidly decreases from 4.1 to 0.29 in the month of June and then remains nearly constant at the same value (≤0.1) in the rest of the season. High values of BR in the first half of June are indicative of intense thermals and convective clouds with higher bases. Low values of BR from July to September period are indicative of weak thermals and convective clouds with lower bases. Intra-seasonal and inter-annual variability of BR is found to be inversely related to precipitation over the region. BR analysis indicates that the land surface characteristics of the study region during July–September are similar to that over oceanic regions as far as intensity of thermals and associated cloud microphysical properties are concerned. Similar variation of BR is found in El Nino and La Nina years. During June, an increasing trend is observed in SHF and BR and decreasing trend in LHF from 1976 to 2014. Increasing trend in the SHF is statistically significant.

The influence of strong horizontal electric field (EH) on different stages of deformation and eventual breakup of the large water drops of 6.6, 7.0, and 7.25mm diameter has been observed in a vertical wind tunnel using high-speed photography. Dumbbell, filament, and bag modes of drop breakup are observed when E-H = 0. However, drops elongate in horizontal direction, mostly develop sharp curvature at their ends, eject a fine jet spray of tiny droplets, and ultimately break up into several droplets in E-H = 500 kVm(-1). Extreme elongation up to 29mm is observed for a 7.0mm diameter drop. Results show that the breakup time, i. e., the time from the drop's extreme prolate shape to its breakup in its final oscillation, ranges from 13 to 41 ms when E-H = 0 and 57-105 ms when E-H = 500 kVm(-1). So although the lifetime of the drop since its suspension to breakup is reduced, its elongation and breakup time increase in EH. It suggests that the effect of E-H in final oscillation before breakup overcomes the effect of hydrodynamic and aerodynamic forces in elongating the drop. Also, no breakup of bag type is observed in E-H = 500 kVm(-1). Moreover, the fragments formed after the drop breakup and tiny droplets ejected by their fragments carry electrical charges of polarity determined by the induced charge on the parent drop in E-H. The significance of the results is discussed in modifying the drop growth and the radar echo-precipitation relationships in thunderclouds.

Rainfall mechanism over the rain-shadow region of north peninsular India during the summer monsoon season has been investigated using dynamic, thermodynamic, cloud microphysics and cloud dynamic (CMCD) forcings. Daily rainfall data has been used to understand rainfall variability. Daily ECMWF wind data for the period 2009–2011 have been used to study the wind divergence, shear and vertical velocity profiles. Daily thermodynamic parameters from upper air soundings of Hyderabad (17.448°N, 78.381°E), have been examined. Aircraft data have been used to study CMCD parameters. The divergence is found between surfaces to 850 hPa level whereas the convergence is at 850 hPa, which comes down to surface level during presence of low pressure systems. The divergence is observed at low (700 hPa), mid (600–300 hPa) and upper (250–150 hPa) tropospheric levels. In consequence of these divergence structures, three types of cloud systems viz. shallow, congestus and deep are developed with bases just above 850 hPa and tops at corresponding three divergent levels. The vertical profiles of relative humidity observed by radiosonde data have been analyzed to get the frequency distribution of shallow, congestus and deep clouds. The highest frequency observed is that of congestus clouds. The thermodynamic structure shows dry surface level and warm and moist middle troposphere with tongues of dry air and multilevel inversions which have been attributed to advection of aerosol-rich dry air. The aircraft observations showed high aerosol concentrations from surface to 5 km, polluted clouds with cloud droplet effective radius smaller than that required for collision–coalescence process. The factors which are responsible for causing low rainfall over the rain-shadow area have been identified.

The time-averaged axis ratios, frequency and amplitude of oscillations of water drops of 2.67–6.6mm diameter were determined by suspending them in a vertical wind tunnel in the absence and presence of horizontal electric fields using a high speed camera at 1000 frames per second. A systematic decrease in the drop's axis-ratio is observed with increase in its diameter and/or horizontal electric field. The results revealed with high speed photography are in good agreement with earlier results. The drop distortion due to horizontal electric field is more pronounced for the drops in the size-range of 3.36–6mm diameter showing that the electrical forces progressively enhance the horizontal elongation of the drop resulting in its instability at 6.6mm. The drop oscillation frequency computed from temporal variation of axis ratio, decreases with increase in drop size but shows no significant change in oscillation frequency in the horizontal electric field of ≤500kVm−1. However, the oscillation amplitude increases with increase in drop size up to a threshold value and then flatten-off in the electric field of ≤300kVm−1 demonstrating the nonlinear effect of net forces acting on such large drops. In higher electric field of 500kVm–1, gradual increase in the amplitude of oscillation with an increase in drop diameter has been observed. Moreover, for a particular drop size, the amplitude of oscillation decreases with increase in the electric field upto 500kVm−1. The oscillation frequency of the waterdrops experiences multimode oscillations. The dominant fundamental mode of oscillations (2,0) always exists for all drops in our experiments along with the coexistence of higher modes of oscillations i.e. (2,1) and (2,2) mode. Possible effects of electrical forces on shape parameters and their implications on cloud microphysics and in radar meteorology are discussed.

Airborne measurements conducted under a special mission over Bay of Bengal (BoB) during the CAIPEEX (Cloud Aerosol Interaction and Precipitation Enhancement EXperiment) in 2011 were analyzed in the present study. Research flights were carried out on 19 and 20 October, 2011 (referred as RF1 and RF2), in the region over BoB, which was influenced by a depression to evaluate the aerosol–cloud interactions over marine environment. The increased concentration of aitken/accumulation mode particles was observed at 500m above sea surface level over the ocean after the passage of the depression. The source of these particles and their subsequent growth during RF1 at about 200km from coastline has been attributed to (i) increased production of aerosols due to oxidation of dimethyl sulfide (DMS) because of upwelling of the deep ocean water during the depression and (ii) anthropogenic aerosols transported from inland. Moreover, measurements of accumulation and coarse mode particles with diameter ranging from 0.1 to 3μm and cloud droplets in the range 3 to 47μm show systematic growth associated with cloud microphysical/rain formation process. On the other hand, no such evidence of increasing particle concentration and growth has been observed at about 60km from coastline towards southeast during RF2. Evidently, the rain event observed during the night hours of 19 October caused the washout and scavenging of aerosols which contributed towards the decreased aerosol concentration observed near the coast.

Measurements of the number concentration and size distribution of aerosol particles in the size range of 0.5–20 μm diameter were made with an aerodynamic particle sizer at an Arctic site at Ny-Alesund, Svalbard in August–September 2007 during the International Polar Year 2007–2008. Data are analyzed to study the aerosol number concentration–wind speed relationships. The sea-salt particles of marine origin generated within the Arctic circle are identified as the main source of the Arctic summer aerosols. Total number concentration of aerosol particles increases with increase in wind speed, the increase being more when winds from open leads over the oceanic sector are reaching the station as compared to when winds from pack ice in other directions are reaching the station. The larger increase with winds from the oceanic sector is attributed to the enhanced bubble-breaking activity and increased entrainment of dimethyl sulphide particles at the sea surface. Although, the increase in total aerosol number concentration associated with the winds from the oceanic sector is spread over the whole range of particle sizes, the increase in coarse mode particles is more prominent than that in the accumulation mode particles. The age of airmass over pack ice is also an important factor to determine the aerosol concentration over the Arctic region. The process of rainout/washout of the aerosol particles due to drizzle/snowfall is an effective sink mechanism in the Arctic environment. The aerosol particle concentration starts decreasing within a few minutes from the start of these events but requires a few hours to restore to the normal background aerosol level after the end of event.

The mechanism responsible for high rainfall over the Indian west coast region has been investigated by studying dynamical, thermodynamical and microphysical processes over the region for the monsoon season of 2009. The European Centre for Medium-Range Weather Forecasts wind and NCEP flux data have been used to study the large scale dynamical parameters. The moist adiabatic and multi-level inversion stratifications are found to exist during the high and low rainfall spells, respectively. In the moist adiabatic stratification regime, shallow and deep convective clouds are found coexisting. The Cloud Aerosol Interaction and Precipitation Enhancement EXperiment aircraft data showed cloud updraft spectrum ranging from 1 to 10 m s−1 having modal speed 1–2.5 m s−1. The low updrafts rates provide sufficient time required for warm rain processes to produce rainfall from shallow clouds. The low cloud liquid water is observed above the freezing level indicating efficient warm rain process. The updrafts at the high spectrum end go above freezing level to generate ice particles produced due to mixed-phase rainfall process from deep convective clouds. With aging, deep convection gets transformed into stratiform type, which has been inferred through the vertical distribution of the large scale omega and heating fields. The stratiform heating, high latent heat flux, strong wind shear in the lower and middle tropospheric levels and low level convergence support the sustenance of convection for longer time to produce high rainfall spell. The advection of warm dry air in the middle tropospheric regions inhibits the convection and produce low rainfall spell. The mechanisms producing these spells have been summarized with the block diagram.

While the demand for enhancing rainfall through cloud seeding is strong and persistent in the country, considerable uncertainty exists on the success of such an endeavour at a given location. To understand the pathways of aerosol cloud interaction through which this might be achieved, a national experiment named Cloud Aerosol Interaction and Precipitation Enhancement EXperiment (CAIPEEX) in two phases, was carried out. The rationale of CAIPEEX, the strategy for conducting the experiment, data quality and potential for path-breaking science are described in this article. Pending completion of quality control and calibration of the CAIPEEX phase-II data, here we present some initial results of CAIPEEX phase-I aimed at documenting the prevailing microphysical characteristics of aerosols and clouds and associated environmental conditions over different regions of the country and under different monsoon conditions with the help of an instrumented research aircraft. First-time simultaneous observations of aerosol, cloud condensation nuclei (CCN) and cloud droplet number concentration (CDNC) over the Ganges Valley during monsoon season show very high concentrations (>1000 cm(-3)) of CCN at elevated layers. Observations of elevated layers with high aerosol concentration over the Gangetic valley extending up to 6 km and relatively less aerosol concentration in the boundary layer are also documented. We also present evidence of strong cloud aerosol interaction in the moist environments with an increase in the cloud droplet effective radius. Our observations also show that pollution increases CDNC and the warm rain depth, and delays its initiation. The critical effective radius for warm rain initiation is found to be between 10 and 12 mu m in the polluted clouds and it is between 12 and 14 mu m in cleaner monsoon clouds.

Measurements of the concentration and size distribution of aerosol particles in the size-ranges of 0.5–20 µm and 16–700 nm diameters were made during six fog episodes over the south Indian Ocean. Observations show that concentrations of particles of all sizes start decreasing 1–2 hours before the occurrence of fog. This decrease is more prominent for coarse particles of >1 µm diameter and continues until 10–20 minutes before the onset of fog when particle concentrations in all size ranges rapidly increase by one/two orders of magnitude in ∼20 minutes. Thereafter, concentrations of particles of all sizes gradually decrease until the dissipation of fog. After the fog dissipation, concentrations of coarse mode particles rapidly increase and restore to their pre-fog levels but concentrations of the Aitken mode particles decrease slowly and reach their pre-fog levels only after 1–2 hours. The net effect of fog is to change the bimodal size distributions of aerosols with a coarse mode at 1.0 µm and an accumulation mode at 40–60 nm to a power law size distribution. It is proposed that the preferential growth and sedimentation of the coarse mode hygroscopic particles in the initial phase cause a large decrease in the aerosol surface area. As a result, the low vapour pressure gases which were initially being used for the growth of coarse mode particles, now accelerate the growth rates of the accumulation and Aitken mode particles.

Concentration and number size distribution of aerosol particles from 4.4 to 168nm diameter are measured at ten latitudinal positions in the Indian Ocean during the Pilot Expedition to Southern Ocean (PESO) from January 23 to March 31, 2004. Total number concentration of particles is minimum in the southern tropical trade wind region and maximum in the roaring forties. Number size distributions follow the power law over the northern Indian Ocean but are monomodal with the maxima lying between 35 and 60nm over the southern Indian Ocean. Particles of diameter as small as 5nm are observed in concentrations of ∼103cm−3 in the roaring forties (e.g. ∼40–50°S). Concentration of particles of <50nm diameter increases with wind speed. Thus, in addition to the ultrafine and Aitken mode particles being transported from the free troposphere to the marine boundary layer with the subsidence following cold frontal passages in the southern mid-latitudes, the wind-generated particles significantly contribute to the ultrafine aerosols down to 5nm diameter in the roaring forties. Observations indicate that while the wind-generated particles dominate at ∼45°S, the particles associated with the subsidence dominate at ∼38°S.

The measurements of total number concentration and number size distribution of aerosols in size ranges of 16-700 nm and 0.5-20 mu m diameters made from 14 degrees N to 56 degrees S in the Indian ocean during January 23 to March 31, 2004, are reported. The average values of total number (mass) concentration of micrometer aerosols (0.5-20 pm) are 7.2 +/- 3 cm(-3) (8.89 mu g m(-3)) from 14 degrees N to the Inter-Tropical Convergence Zone (ITCZ), 4.6 +/- 2 cm(-3) (4.9 mu g m(-3)) in the ITCZ, 3.0 +/- 1.4 cm(-3) (5.78 mu g m(-3)) in the trade wind region from 8 degrees-30 degrees S, 3.8 +/- 2.6 cm(-3) (7.9 mu g m(-3)) from 30 degrees-40 degrees S, and 5.8 +/- 3.5 cm(-3) (9.65 mu g m(-3)) in the roaring forties from 40 degrees-56 degrees S. Latitudinal distribution of such aerosols shows that their number concentration is minimum (0.5 cm(-3)) at 11 degrees S and increases on either side of this location. Size distributions of micrometer aerosols in all latitudinal belts show a maxima in coarse mode at 0.5-1.5 PM diameter. The correlation coefficient in the aerosol concentration-wind speed relations of these aerosols is observed to differ in different latitudinal belts and has maximum value in the belt of strongest winds. Also, diurnal variations of the average aerosol concentration and wind speed show some similarity in belts of strong winds.Total number concentration of submicrometer (16-700 nm) particles is also minimum in the southern trade wind region and their size distribution is bimodal with maxima in Aitken mode (similar to 50 nm) and accumulation mode (similar to 130 nm). South of the ITCZ, concentrations of both, total number and Aitken mode particles normally increase with latitude. The increase in Aitken mode particles at high latitudes is large enough for the Aitken mode maxima to superimpose the accumulation mode maxima. Observations suggest that addition of Aitken particles is so fast that process of coagulation is not able to reach equilibrium to develop a distinct accumulation maxima.Observations show that pristine air of the trade wind region in the Southern Hemisphere can be advected to mid-latitudes along the ridge developed between anticyclonic and cyclonic systems. (C) 2008 Elsevier B.V. All rights reserved.

Measurements of the number concentration and size distribution of aerosols in the range of 0.5–20 μm diameter were made during a severe cyclonic storm in the Southern Hemisphere at 53.3°S, 52.5°E on 19 February 2004. Data were analyzed to study the aerosol number concentration–wind speed relationship. It was found that in conformity with past observations, total aerosol number concentration increases with increase in wind speed from 4 to 11 m s−1, measured at 10 m above sea level. However, contrary to most of the earlier studies, total aerosol number concentration decreases with increase in the wind speed from 16 to 22 m s−1 and then maintains an almost constant value up to the maximum wind speed of 33.1 m s−1. The total aerosol number concentration varies a little with wind speed in the range of 11–16 m s−1. While increase in the total aerosol number concentration corresponding to the increase in wind speed from 4 to 11 m s−1 is spread over the whole range of particle sizes, decrease in the aerosol number concentration associated with increase in wind speed from 16 to 22 m s−1 is mainly due to decrease in the concentration of particles of <1 μm. The increase in aerosol number concentration is well recognized as being due to the enhanced bubble‐breaking activity at the sea surface and increased entrainment of sea‐salt particles, once produced. We propose that decrease in the aerosol number concentration may possibly occur because of the scavenging of aerosols by larger seawater drops injected into the atmosphere at high wind speeds. This scavenging process may act as a built‐in sink, which becomes operative at high wind speeds and restricts the enhancement in concentration of marine aerosols.

Concentration and size distribution of aerosol particles in the size range of 0.5 to 20.0 mu m were measured over the Indian Ocean during January 23 to March 31, 2004. Total aerosol concentration showed the North-to-South positive gradient with latitude over the Indian Ocean North of the Inter Tropical Convergence Zone (ITCZ). Minimum concentration of aerosols was observed immediately South of the ITCZ and it increased on either side of the ITCZ. Contrary to being monomodal in shape in this size range as is generally expected over open ocean, the aerosol size distributions followed the Junge's power law and show the transport of aerosols from the Indian subcontinent to North of the ITCZ, even though several hundreds of kilometers away from the Indian coastline. Aerosols South of the ITCZ exhibited monomodal size distributions which were typical of marine aerosols in the pristine environments. Aerosol size distributions in the roaring forties clearly showed the generation of sea-salt particles due to the wave breaking activity in this region of high winds. Abundance of particles of < 1.0 mu m diameter dominated over the Indian Ocean North of the ITCZ.

In order to understand the sampling time effect on the 2,4-TDI (Toluene diisocyanate) concentrations, laboratory and field tests were conducted in this study. An ADS (annular denuder sampler) and two OFFCs (open face filter holders) with different filters were tested for 1 to 120 minutes in the laboratory using 2,4-TDI gas. In the field study, the standard sampling method, the dual filter the triple filter and annular denuder systems were used at two workplaces to study the change of 2,4-TDI concentrations with sampling time from 15 to 60 minutes. The test results in both laboratory and field studies show that the sampling time influences the sampled TDI concentration considerably which may be due to reaction of TDI with water vapor and polyo in the sampling process. It is evident that as sampling time increases the TDI concentration decreases very significantly.

An aerosol charge analyzer has been constructed to measure the charge distribution of NaCl particles generated in the laboratory. A radioactive electrostatic charge neutralizer utilizing Po‐210 was used to neutralize the electrostatic charge of the particles. The atomization technique was used to generate NaCl particles with diameters of 0.2 to 0.8 μm, while the evaporation and condensation method was adopted to generate particles of 0.01 to 0.2 μm in diameter. The experimental data demonstrates that the absolute average particle charge depends on the particle diameter, and is higher than that calculated by the Boltzmann charge equilibrium for particles within the range of 0.2 to 0.8 μm. The charge increases with decreasing NaCl concentration. When these particles are neutralized using the Po‐210 neutralizer, it is found that the electrostatic charge reaches the Boltzmann charge equilibrium. For 0.01 to 0.2 μm NaCl particles generated using the evaporation and condensation method, test results show that the absolute average particle charge is higher than that calculated by the Boltzmann charge equilibrium for particles larger than 0.03 to 0.05 μm in diameter, while it is lower than that predicted by the Fuchs theory [1], for particles smaller than 0.03 to 0.05 μm. However, after charge neutralization, particles with diameter above 0.05 μm reach the Boltzmann charge equilibrium condition, and the charges for particles with diameters of 0.010 to 0.05 μm, agree well with Fuchs' theory.

The main objective of this study is to investigate the personal or area exposure of organic solvents during paint stripping and paint spraying. Three aircraft paint stripping/spraying workplaces in Taiwan were selected, and the Council of Labor Affairs and NIOSH recommended sampling/analytical methods used in this study. Activated charcoal tubes were used to investigate the personal and area exposure concentration of organic solvents in paint stripping and paint spraying operations. During aircraft paint stripping, experiment results show that methylene chloride personal exposure concentration at the ground area, 42.01+/-31.86 ppm, is higher than that at the working platform 4 M high above the ground, 20.41+/-11.43 ppm. Exposure concentration of methylene chloride in the initial paint stripping operation stage of every workplace is over the PEL (50 ppm) set by the Taiwan Council of Labor Affairs. Corrective actions are needed. During paint spraying, concentrations of all organic solvents were found to be below the PEL of OSHA.