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1.
Background
A proposed strategy for immobilizing trace metals in the subsurface is to stimulate calcium carbonate precipitation and incorporate contaminants by co-precipitation. Such an approach will require injecting chemical amendments into the subsurface to generate supersaturated conditions that promote mineral precipitation. However, the formation of reactant mixing zones will create gradients in both the saturation state and ion activity ratios (i.e., ). To better understand the effect of ion activity ratios on CaCO3 precipitation kinetics and Sr2+ co-precipitation, experiments were conducted under constant composition conditions where the supersaturation state (Ω) for calcite was held constant at 9.4, but the ion activity ratio was varied between 0.0032 and 4.15. 相似文献2.
Ravi Yadav L. K. Sahu S. N. A. Jaaffrey G. Beig 《Journal of Atmospheric Chemistry》2014,71(2):125-144
Continuous in-situ measurements of surface ozone (O3), carbon monoxide (CO) and oxides of nitrogen (NOx) were conducted at Udaipur city in India during April 2010 to March 2011. We have analyzed the data to investigate both diurnal and seasonal variations in the mixing ratios of trace gases. The diurnal distribution of O3 showed highest values in the afternoon hours and lower values from evening till early morning. The mixing ratios of CO and NOx showed a sharp peak in the morning hours but lowest in the afternoon hours. The daily mean data of O3, CO and NOx varied in the ranges of 5–51 ppbv, 145–795 ppbv and 3–25 ppbv, respectively. The mixing ratios of O3 were highest of 28 ppbv and lowest 19 ppbv during the pre-monsoon and monsoon seasons, respectively. While the mixing ratios of both CO and NOx showed highest and lowest values during the winter and monsoon seasons, respectively. The diurnal pattern of O3 is mainly controlled by the variations in photochemistry and planetary boundary layer (PBL) depth. On the other hand, the seasonality of O3, CO and NOx were governed by the long-range transport associated mainly with the summer and winter monsoon circulations over the Indian subcontinent. The back trajectory data indicate that the seasonal variations in trace gases were caused mainly by the shift in long-range transport pattern. In monsoon season, flow of marine air and negligible presence of biomass burning in India resulted in lowest O3, CO and NOx values. The mixing ratios of CO and NOx show tight correlations during winter and pre-monsoon seasons, while poor correlation in the monsoon season. The emission ratio of ?CO/?NOx showed large seasonal variability but values were lower than those measured over the Indo Gangetic Plains (IGP). The mixing ratios of CO and NOx decreased with the increase in wind speed, while O3 tended to increase with the wind speed. Effects of other meteorological parameters in the distributions of trace gases were also noticed. 相似文献
3.
Spatiotemporal variations of the quasi-biennial oscillation (QBO) in temperature and ozone over the tropical–subtropical belts (40°N–40°S) have been studied using Microwave Limb Sounder data for the period 1992–1999. Wavelet analysis has been performed to study inter-annual variations in amplitude and phases of the QBO. Latitude-height cross-sections of the amplitudes of temperature and ozone QBO exhibit a double-peak structure near the equator. Phase structure reveals that the temperature QBO descended faster than the ozone QBO. Cross-wavelet analysis shows an anti-phase relation between the amplitudes of the temperature and ozone QBO in the upper stratospheric region, whereas in-phase relation exists in the middle stratospheric region. 相似文献
4.
5.
Summary Latitude-altitude structure of ozone QBO over the tropical-subtropical stratosphere (40° S–40° N) has been explored by analyzing
Microwave Limb Sounder (MLS) aboard Upper Atmospheric Research Satellite (UARS) data for the period 1992–1999 using the multifunctional
regression model. The inferred ozone QBO shows two maxima located at 22 hPa and 10 hPa with coefficient of 2–3% per 10 m/s
centered at the equator. The equatorial maxima are out of phase with each other. Subtropics exhibit two peak structure near
14 hPa but of opposite sign to that of equatorial maximum near 10 hPa. Over the equatorial region, positive (zonal winds westerly)
coefficients overlay negative (zonal winds easterlies) coefficients which descend with time. A pattern of equatorial maximum
and two subtropical minima appears in the months December to February near 10 hpa and it propagates upward with progression
of seasons. Equatorial QBO is seasonally asynchronous while subtropical QBO is seasonally synchronous.
Correspondence: Suvarna Fadnavis, Physical Meteorology and Aerology Division, Indian Institute of Tropical Meteorology, Dr.
Homi Bhabha Road, Pashan, Pune 411008, India 相似文献
6.
There has been a considerable improvement in the knowledge of stratospheric positive ion chemistry during the last decade. Results of several in-situ measurements of ion composition have been reported. Total ion density has also been measured with greater accuracy. In this work, theoretical study has been made to reproduce the main features of the above observations. Difficulties encountered in such studies are discussed. Finally models of total ion density and ion composition are given. 相似文献
7.
Kaushar Ali A. S. Panicker G. Beig R. Srinivas P. Acharja 《Journal of Atmospheric Chemistry》2016,73(1):1-27
Sampling of particulate matter with aerodynamic diameter cut off at 2.5 μm (PM2.5) has been carried out over a semi urban site of Pune and an urban site of Hyderabad. Analysis of elemental Carbon (EC) and Organic Carbon (OC) present in PM2.5 was carried out using advanced Desert Research Institute’s (DRI) Thermal/Optical Carbon Analyzer operated on IMPROVE_ A (Interagency Monitoring of Protected Visual Environments_ A) protocol. It is found that average concentration of EC and OC both at Pune and Hyderabad was highest during winter season and lowest during monsoon season. Winter high is mainly controlled by inversion, whereas monsoon low is due to rain-out and wash-out process. OC/EC ratio showed higher variation over Pune compared to that over Hyderabad in different seasons, indicating divergent sources of emission of OC and EC at Pune. Formation of Secondary Organic Carbon (SOC) has also been identified as one of the reasons for wide variation in OC/EC ratio value in different seasons over both the sites. 相似文献
8.
Below-cloud aerosol scavenging is generally estimated from field measurements using advanced instruments that measure changes in aerosol distributions with respect to rainfall. In this study, we discuss various scavenging mechanisms and scavenging coefficients from past laboratory and field measurements. Scavenging coefficients derived from field measurements (representing natural aerosols scavenging) are two orders higher than that of theoretical ones for smaller particles (Dp < 2 μm). Measured size-resolved scavenging coefficients can be served as a better option to the default scavenging coefficient (e.g. a constant of 10?4 s?1 for all size of aerosols, as used in the CALPUFF model) for representing below-cloud aerosol scavenging. We propose scavenging correction parameter (CR) as an exponential function of size-resolved scavenging coefficients, winds and width in the downwind of the source–receptor system. For a wind speed of 3 m s?1, CR decrease with the width in the downwind for particles of diameters Dp < 0.1 μm but CR does not vary much for particles in the accumulation mode (0.1 < Dp < 2 μm). For a typical urban aerosol distribution, assuming 3 m s?1 air-flow in the source–receptor system, 10 km downwind width, 2.84 mm h?1 of rainfall and using aerosol size dependent scavenging coefficients in the CR, scavenging of aerosols is found to be 16% in number and 24% in volume of total aerosols. Using the default scavenging coefficient (10?4 s?1) in the CALPUFF model, it is found to be 64% in both number and volume of total aerosols. 相似文献
9.
Sachin D. Ghude S. L. Jain B. C. Arya G. Beig Y. N. Ahammed Arun Kumar B. Tyagi 《Journal of Atmospheric Chemistry》2008,60(3):237-252
Seven year data of hourly surface ozone concentration is analyzed to study diurnal cycle, trends, excess of ozone levels above
threshold value and cumulative ozone exposure indices at a tropical megacity, Delhi. The ozone levels clearly exhibit a diurnal
cycle, similar to what has been found in other urban places. A sharp increase in the ozone levels during forenoon and a sharp
decrease in the early afternoon can be observed. The average rate of increase in ozone concentration between 09 and 12 h has
been observed to be 7.1 ppb h−1. We find that the daily maximum and daytime 8-h (10–17 h) ozone levels are increasing at a rate of about 1.7 (± 0.7) and
1.3 (± 0.56) ppb y−1, respectively. The directives on ozone pollution in ambient air provided by United Nations Economic Commission for Europe
and World Health Organization for vegetation (AOT40) and human health protection were used to assess the air quality. The
present surface ozone levels in the city are high enough to exceed “Critical Levels” which are considered to be safe for human
health, vegetation and forest. The human health threshold was exceeded for up to ~45 days per year. The AOT40 (Accumulated
exposure Over a Threshold of 40 ppb) threshold was exceeded significantly during winter (D-J-F) and pre-monsoon (M-A-M) (Rabi
crop growing season) season in India. Translating AOT40 exceedances during pre-monsoon into relative yield loss we estimate
yield loss of 22.7%, 22.5%, 16.3% and 5.5% for wheat, cotton, soybean and rice, respectively. 相似文献
10.
Simultaneous observations of surface ozone (O3) with its precursors namely, carbon monoxide (CO) and oxides of nitrogen (NOx) have been taken on diurnal scale from a tropical semi-urban site, Pune (18.54°N, 73.81°E) in India. We present the data
for one year (2003–2004) period to study the salient features of these trace gases. The peak in amplitude of ozone is found
during the noontime whereas in CO and NOX it is observed in the morning hours between 0800 and 0900 H. The concentration of these pollutants drop down considerably
during southwest monsoon months and the diurnal pattern also become very weak. The diurnal trends of these gases are found
to be different for different seasons, which are specific to the receptor site. Model simulations using 3-D chemical-transport
model with regional emission inventories and observed winds have also been carried out. The comparison of model results with
observations, on seasonal basis yielded a reasonable qualitative agreement. The relative role of local emissions and long
range transport in the diurnal pattern for different seasons has been outlined, which reveals that the ozone is highly influenced
by regional/long range transport in this region. The effect of precursor amounts in the morning on afternoon ozone peak levels
has been investigated using the lag correlation study, which reveals that a time lag of 5–7 h is required for most of these
precursor gases to photo-chemically produce ozone to its maximum potential. Results are discussed in the light of available
topographic and meteorological conditions. 相似文献