scholarly journals Comparative assessment of aerosol optical properties over a mega city and an adjacent urban area in India

MAUSAM ◽  
2021 ◽  
Vol 68 (4) ◽  
pp. 673-688
Author(s):  
KANIKA TANEJA ◽  
S. D. ATTRI ◽  
SHAMSHAD AHMAD ◽  
KAFEEL AHMAD ◽  
V. K. SONI ◽  
...  
Keyword(s):  
Optical Properties ◽  
Urban Area ◽  
Biomass Burning ◽  
Monsoon Season ◽  
Single Scattering ◽  
Absolute Difference ◽  
Industrial Emissions ◽  
Aerosol Optical Properties ◽  
The Difference ◽  
Lower Magnitude

The present work revolves around the comparative analysis of aerosol optical properties in a mega city, Delhi and in a nearby urban area, Rohtak. It is pertinent to note that despite of the close proximity and similar meteorological conditions, the two study locations show significant differences in aerosol characteristics. The study is conducted using ground based Sky-radiometer measurements for a period of one year. The mean annual Aerosol Optical Depth (AOD) at 500 nm over Delhi and Rohtak is observed to be 1.01 and 0.73 respectively, with correlation coefficient of 0.67 and mean absolute difference of 0.51. The magnitude of AOD in Delhi is higher than in Rohtak throughout the year, except in post-monsoon season. The difference in Angstrom exponent (alpha) between the stations is minimal. However, lower magnitude of alpha is observed in Rohtak, indicating presence of more concentration of coarse-mode particles. Single Scattering Albedo (SSA) also shows seasonal variation with significantly lower values in Delhi throughout the year, indicating contribution of absorbing type of aerosols (like black carbon). The volume concentration in fine-size is found to be higher in Delhi than in Rohtak, indicating combined effect of dust, vehicular, biomass burning and industrial emissions. The aerosol classification via relationship between AOD and alpha shows that urban/biomass burning (U/B) aerosols are dominant in Delhi and mixed type (MT) aerosols in Rohtak during winter and pre-monsoon.

scholarly journals STUDY OF AEROSOL OPTICAL PROPERTIES OVER TWO SITES IN THE FOOTHILLS OF THE CENTRAL HIMALAYAS

2018 ◽  
Vol XLII-3 ◽  
pp. 1493-1497 ◽  
Author(s):  
D. Rupakheti ◽  
S. Kang ◽  
Z. Cong ◽  
M. Rupakheti ◽  
L. Tripathee ◽  
...  
Keyword(s):  
Optical Properties ◽  
Biomass Burning ◽  
Asymmetry Parameter ◽  
Monsoon Season ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Aerosol Optical Properties ◽  
Central Himalayas ◽  
Aerosol Types ◽  
Volume Size

Atmospheric aerosol possesses impacts on climate system and ecological environments, human health and agricultural productivity. The environment over Himalayas and Tibetan Plateau region are continuously degraded due to the transport of pollution from the foothills of the Himalayas; mostly the Indo-Gangetic Plain (IGP). Thus, analysis of aerosol optical properties over two sites; Lumbini and Kathmandu (the southern slope of central Himalayas) using AERONET’s CIMEL sun photometer were conducted in this study. Aerosol optical depth (AOD at 500 nm), angstrom exponent (α or AE), volume size distribution (VSD), single scattering albedo (SSA) and asymmetry parameter (AP) were studied for 2013–2014 and the average AOD was found to be: 0.64 ± 0.41 (Lumbini) and 0.45 ± 0.30 (Kathmandu). The average AE was found to be: 1.25 ± 0.24 and 1.26 ± 0.18 respectively for two sites. The relation between AOD and AE was used to discriminate the aerosol types over these sites which indicated anthropogenic, mixed and biomass burning origin aerosol constituted the major aerosol types in Lumbini and Kathmandu. A clear bi-modal distribution of aerosol volume size was observed with highest volume concentration during the post-monsoon season in fine mode and pre-monsoon season in coarse mode (Lumbini) and highest value over both modes during pre-monsoon season in Kathmandu. The single scattering albedo (SSA) and asymmetry parameter (AP) analyses suggested aerosols over the Himalayan foothills sites are dominated by absorbing and anthropogenic aerosols from urban and industrial activities and biomass burning. Long-term studies are essential to understand and characterize the nature of aerosol over this research gap zone.

scholarly journals Intercomparison of biomass burning aerosol optical properties from in situ and remote-sensing instruments in ORACLES-2016

2019 ◽  
Vol 19 (14) ◽  
pp. 9181-9208 ◽  
Author(s):  
Kristina Pistone ◽  
Jens Redemann ◽  
Sarah Doherty ◽  
Paquita Zuidema ◽  
Sharon Burton ◽  
...  
Keyword(s):  
Optical Properties ◽  
Case Studies ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Measurement Techniques ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Aerosol Optical Properties ◽  
Biomass Burning Aerosol

Abstract. The total effect of aerosols, both directly and on cloud properties, remains the biggest source of uncertainty in anthropogenic radiative forcing on the climate. Correct characterization of intensive aerosol optical properties, particularly in conditions where absorbing aerosol is present, is a crucial factor in quantifying these effects. The southeast Atlantic Ocean (SEA), with seasonal biomass burning smoke plumes overlying and mixing with a persistent stratocumulus cloud deck, offers an excellent natural laboratory to make the observations necessary to understand the complexities of aerosol–cloud–radiation interactions. The first field deployment of the NASA ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) campaign was conducted in September of 2016 out of Walvis Bay, Namibia. Data collected during ORACLES-2016 are used to derive aerosol properties from an unprecedented number of simultaneous measurement techniques over this region. Here, we present results from six of the eight independent instruments or instrument combinations, all applied to measure or retrieve aerosol absorption and single-scattering albedo. Most but not all of the biomass burning aerosol was located in the free troposphere, in relative humidities typically ranging up to 60 %. We present the single-scattering albedo (SSA), absorbing and total aerosol optical depth (AAOD and AOD), and absorption, scattering, and extinction Ångström exponents (AAE, SAE, and EAE, respectively) for specific case studies looking at near-coincident and near-colocated measurements from multiple instruments, and SSAs for the broader campaign average over the month-long deployment. For the case studies, we find that SSA agrees within the measurement uncertainties between multiple instruments, though, over all cases, there is no strong correlation between values reported by one instrument and another. We also find that agreement between the instruments is more robust at higher aerosol loading (AOD400>0.4). The campaign-wide average and range shows differences in the values measured by each instrument. We find the ORACLES-2016 campaign-average SSA at 500 nm (SSA500) to be between 0.85 and 0.88, depending on the instrument considered (4STAR, AirMSPI, or in situ measurements), with the interquartile ranges for all instruments between 0.83 and 0.89. This is consistent with previous September values reported over the region (between 0.84 and 0.90 for SSA at 550nm). The results suggest that the differences observed in the campaign-average values may be dominated by instrument-specific spatial sampling differences and the natural physical variability in aerosol conditions over the SEA, rather than fundamental methodological differences.

scholarly journals Intercomparison of biomass burning aerosol optical properties from in-situ and remote-sensing instruments in ORACLES-2016

2019 ◽  
Author(s):  
Kristina Pistone ◽  
Jens Redemann ◽  
Sarah Doherty ◽  
Paquita Zuidema ◽  
Sharon Burton ◽  
...  
Keyword(s):  
Optical Properties ◽  
Case Studies ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Measurement Techniques ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Aerosol Optical Properties ◽  
Biomass Burning Aerosol

Abstract. The total effect of aerosols, both directly and on cloud properties, remains the biggest source of uncertainty in anthropogenic radiative forcing on the climate. Correct characterization of intensive aerosol optical properties, particularly in conditions where absorbing aerosol is present, is a crucial factor in quantifying these effects. The Southeast Atlantic Ocean (SEA), with seasonal biomass burning smoke plumes overlying and mixing with a persistent stratocumulus cloud deck, offers an excellent natural laboratory to make the observations necessary to understand the complexities of aerosol-cloud-radiation interactions. The first field deployment of the NASA ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) campaign was conducted in September of 2016 out of Walvis Bay, Namibia. Data collected during ORACLES-2016 are used to derive aerosol properties from an unprecedented number of simultaneous measurement techniques over this region. Here we present results from six of the eight independent instruments or instrument combinations, all applied to measure or retrieve aerosol absorption and single scattering albedo. Most but not all of the biomass-burning aerosol was located in the free troposphere, in relative humidities typically ranging up to 60 %. We present the single scattering albedo (SSA), absorbing and total aerosol optical depth (AOD and AAOD), and absorption, scattering, and extinction Ångström exponents (AAE, SAE, EAE) for specific case studies looking at near-coincident and -colocated measurements from multiple instruments, and SSAs for the broader campaign average over the monthlong deployment. For the case studies, we find that SSA agrees within the measurement uncertainties between multiple instruments, though, over all cases, there is no strong correlation between values reported by one instrument and another. We also find that agreement between the instruments is more robust at higher aerosol loading (AOD400 > 0.4). The campaign-wide average and range shows differences in the values measured by each instrument. We find the ORACLES-2016 campaign-average SSA at 500 nm (SSA500) to be between 0.85 and 0.88, depending on the instrument considered (4STAR, AirMSPI, or in situ measurements), with the inter-quartile ranges for all instruments between 0.83 and 0.89. This is consistent with previous September values reported over the region (between 0.84 and 0.90 for SSA at 550 nm). The results suggest that the differences observed in the campaign-average values may be dominated by instrument-specific spatial sampling differences and the natural physical variability in aerosol conditions over the SEA, rather than fundamental methodological differences.

scholarly journals Aerosol optical properties at Lampedusa (Central Mediterranean) – 2. Determination of single scattering albedo at two wavelengths for different aerosol types

2005 ◽  
Vol 5 (4) ◽  
pp. 4971-5005 ◽  
Author(s):  
D. Meloni ◽  
A. di Sarra ◽  
G. Pace ◽  
F. Monteleone
Keyword(s):  
Optical Properties ◽  
Aerosol Optical Depth ◽  
Biomass Burning ◽  
Surface Albedo ◽  
Single Scattering ◽  
Asymmetry Factor ◽  
Aerosol Optical Properties ◽  
Central Mediterranean ◽  
Desert Dust ◽  
Aerosol Types

Abstract. Aerosol optical properties were retrieved from direct and diffuse spectral irradiance measurements made by a multi-filter rotating shadowband radiometer (MFRSR) at the island of Lampedusa (35.5° N, 12.6° E), in the Central Mediterranean, in the period July 2001–September 2003. In a companion paper (Pace et al., 2005) the aerosol optical depth (AOD) and Ångström exponent were used together with airmass backward trajectories to identify and classify different aerosol types. The MFRSR diffuse-to-direct ratio (DDR) at 415.6 nm and 868.7 nm for aerosol classified as biomass burning-urban/industrial, originating primarily from the European continent, and desert dust, originating from the Sahara, is used in this study to estimate the aerosol single scattering albedo (SSA). A detailed radiative transfer model is initialized with the measured aerosol optical depth; calculations are performed at the two wavelengths varying the SSA values until the modelled DDR matches the MFRSR observations. Sensitivity studies are performed to estimate how uncertainties on AOD, DDR, asymmetry factor (g), and surface albedo influence the retrieved SSA values. The results show that a 3% variation of AOD or DDR produce a change of about 0.02 in the retrieved SSA value at 415.6 and 868.7 nm; a ±0.06 variation of the asymmetry factor g produces a change of the estimated SSA of <0.04 at 415.6 nm, and <0.06 at 868.7 nm; finally, an increase of the assumed surface albedo of 0.05 gives very small changes (0.01–0.02) in the retrieved SSA. The calculations show that the SSA of desert dust (DD) increases with wavelength, from 0.81±0.05 at 415.6 nm to 0.94±0.05 at 868.7 nm; on the contrary, the SSA of urban/industrial (UN) aerosols decreases from 0.96±0.02 at 415.6 nm to 0.87±0.07 at 868.7 nm; the SSA of biomass burning (BB) particles is 0.82±0.04 at 415.6 nm and 0.80±0.05 at 868.7 nm. Episodes of UN aerosols occur usually in June and July; BB aerosol episodes with large AOD and long duration are observed mainly in July and August, the driest months of the year, when the development of fires is favoured.

scholarly journals Radiative heating rate profiles over the southeast Atlantic Ocean during the 2016 and 2017 biomass burning seasons

2020 ◽  
Vol 20 (16) ◽  
pp. 10073-10090
Author(s):  
Allison B. Marquardt Collow ◽  
Mark A. Miller ◽  
Lynne C. Trabachino ◽  
Michael P. Jensen ◽  
Meng Wang
Keyword(s):  
Optical Properties ◽  
Atlantic Ocean ◽  
Biomass Burning ◽  
Single Scattering ◽  
Radiative Heating ◽  
Aerosol Layer ◽  
Aerosol Optical Properties ◽  
Ascension Island ◽  
Biomass Burning Aerosol ◽  
Aerosol Plume

Abstract. Marine boundary layer clouds, including the transition from stratocumulus to cumulus, are poorly represented in numerical weather prediction and general circulation models. Further uncertainties in the cloud structure arise in the presence of biomass burning carbonaceous aerosol, as is the case over the southeast Atlantic Ocean, where biomass burning aerosol is transported from the African continent. As the aerosol plume progresses across the southeast Atlantic Ocean, radiative heating within the aerosol layer has the potential to alter the thermodynamic environment and therefore the cloud structure; however, limited work has been done to quantify this along the trajectory of the aerosol plume in the region. The deployment of the first Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF1) in support of the Layered Atlantic Smoke Interactions with Clouds field campaign provided a unique opportunity to collect observations of cloud and aerosol properties during two consecutive biomass burning seasons during July through October of 2016 and 2017 over Ascension Island (7.96∘ S, 14.35∘ W). Using observed profiles of temperature, humidity, and clouds from the field campaign alongside aerosol optical properties from Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2), as input for the Rapid Radiation Transfer Model (RRTM), profiles of the radiative heating rate due to aerosols and clouds were computed. Radiative heating is also assessed across the southeast Atlantic Ocean using an ensemble of back trajectories from the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. Idealized experiments using the RRTM with and without aerosols and a range of values for the single-scattering albedo (SSA) demonstrate that shortwave (SW) heating within the aerosol layer above Ascension Island can locally range between 2 and 8 K d−1 depending on the aerosol optical properties, though impacts of the aerosol can be felt elsewhere in the atmospheric column. When considered under clear conditions, the aerosol has a cooling effect at the TOA, and based on the observed cloud properties at Ascension Island, the cloud albedo is not large enough to overcome this. Shortwave radiative heating due to biomass burning aerosol is not balanced by additional longwave (LW) cooling, and the net radiative impact results in a stabilization of the lower troposphere. However, these results are extremely sensitive to the single-scattering albedo assumptions in models.

scholarly journals Aerosol optical properties at Lampedusa (Central Mediterranean). 2. Determination of single scattering albedo at two wavelengths for different aerosol types

2006 ◽  
Vol 6 (3) ◽  
pp. 715-727 ◽  
Author(s):  
D. Meloni ◽  
A. di Sarra ◽  
G. Pace ◽  
F. Monteleone
Keyword(s):  
Optical Properties ◽  
Aerosol Optical Depth ◽  
Biomass Burning ◽  
Surface Albedo ◽  
Single Scattering ◽  
Asymmetry Factor ◽  
Aerosol Optical Properties ◽  
Central Mediterranean ◽  
Desert Dust ◽  
Aerosol Types

Abstract. Aerosol optical properties were retrieved from direct and diffuse spectral irradiance measurements made by a multi-filter rotating shadowband radiometer (MFRSR) at the island of Lampedusa (35.5° N, 12.6° E), in the Central Mediterranean, in the period July 2001–September 2003. In a companion paper (Pace et al., 2006) the aerosol optical depth (AOD) and Ångström exponent were used together with airmass backward trajectories to identify and classify different aerosol types. The MFRSR diffuse-to-direct ratio (DDR) at 415.6 nm and 868.7 nm for aerosol classified as "biomass burning-urban/industrial", originating primarily from the European continent, and desert dust, originating from the Sahara, is used in this study to estimate the aerosol single scattering albedo (SSA). A detailed radiative transfer model is initialised with the measured aerosol optical depth; calculations are performed at the two wavelengths varying the SSA values until the modelled DDR matches the MFRSR observations. Sensitivity studies are performed to estimate how uncertainties on AOD, DDR, asymmetry factor (g), and surface albedo influence the retrieved SSA values. The results show that a 3% variation of AOD or DDR produce a change of about 0.02 in the retrieved SSA value at 415.6 and 868.7 nm; a ±0.06 variation of the asymmetry factor g produces a change of the estimated SSA of <0.04 at 415.6 nm, and <0.06 at 868.7 nm; finally, an increase of the assumed surface albedo of 0.05 causes very small changes (0.01–0.02) in the retrieved SSA. The calculations show that the SSA of desert dust (DD) increases with wavelength, from 0.81±0.05 at 415.6 nm to 0.94±0.05 at 868.7 nm; on the contrary, the SSA of urban/industrial (UN) aerosols decreases from 0.96±0.02 at 415.6 nm to 0.87±0.07 at 868.7 nm; the SSA of biomass burning (BB) particles is 0.82±0.04 at 415.6 nm and 0.80±0.05 at 868.7 nm. Episodes of UN aerosols occur usually in June and July; long lasting BB aerosol episodes with large AOD are observed mainly in July and August, the driest months of the year, when the development of fires is frequent.

scholarly journals Seasonal cycle and source analyses of aerosol optical properties in a semi-urban environment at Puijo station in Eastern Finland

2012 ◽  
Vol 12 (12) ◽  
pp. 5647-5659 ◽  
Author(s):  
A. Leskinen ◽  
A. Arola ◽  
M. Komppula ◽  
H. Portin ◽  
P. Tiitta ◽  
...  
Keyword(s):  
Optical Properties ◽  
Paper Mill ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Scattering Coefficient ◽  
Traffic Density ◽  
Aerosol Optical Properties ◽  
Absorption Coefficients ◽  
Data Set ◽  
Pollutant Sources

Abstract. We introduce a four-year (in 2006–2010) continuous data set of aerosol optical properties at Puijo in Kuopio, Finland. We study the annual and diurnal variation of the aerosol scattering and absorption coefficients, hemispheric backscattering fraction, scattering Ångström exponent, and single scattering albedo, whose median values over this period were 7.2 Mm−1 (at 550 nm), 1.0 Mm−1 (at 637 nm), 0.15, 1.93 (between 450 and 550 nm), and 0.85, respectively. The scattering coefficient peaked in the spring and autumn, being 2–4 times those in the summer and winter. An exception was the summer of 2010, when the scattering coefficient was elevated to ~300 Mm−1 by plumes from forest fires in Russia. The absorption coefficient peaked in the winter when soot-containing particles derived from biomass burning were present. The higher relative absorption coefficients resulted in lower single scattering albedo in winter. The optical properties varied also with wind direction and time of the day, indicating the effect of the local pollutant sources and the age of the particles. Peak values in the single scattering albedo were observed when the wind blew from a paper mill and from the sector without local pollutant sources. These observations were linked, respectively, to the sulphate-rich aerosol from the paper mill and the oxygenated organics in the aged aerosol, which both are known to increase the scattering characteristics of aerosols. Decreases in the single scattering albedo in the morning and afternoon, distinct in the summertime, were linked to the increased traffic density at these hours. The scattering and absorption coefficients of residential and long-range transported aerosol (two separate cloud events) were found to be decreased by clouds. The effect was stronger for the scattering than absorption, indicating preferential activation of the more hygroscopic aerosol with higher scattering characteristics.

scholarly journals Tropical biomass burning smoke plume size, shape, reflectance, and age based on 2001–2009 MISR imagery of Borneo

2012 ◽  
Vol 12 (7) ◽  
pp. 3437-3454 ◽  
Author(s):  
C. S. Zender ◽  
A. G. Krolewski ◽  
M. G. Tosca ◽  
J. T. Randerson
Keyword(s):  
Optical Properties ◽  
Tropical Forests ◽  
Optical Depth ◽  
Biomass Burning ◽  
Single Scattering ◽  
Particle Dispersion ◽  
Hygroscopic Growth ◽  
Smoke Plume ◽  
Fire Emissions ◽  
Plume Geometry

Abstract. Land clearing for crops, plantations and grazing results in anthropogenic burning of tropical forests and peatlands in Indonesia, where images of fire-generated aerosol plumes have been captured by the Multi-angle Imaging SpectroRadiometer (MISR) since 2001. Here we analyze the size, shape, optical properties, and age of distinct fire-generated plumes in Borneo from 2001–2009. The local MISR overpass at 10:30 a.m. misses the afternoon peak of Borneo fire emissions, and may preferentially sample longer plumes from persistent fires burning overnight. Typically the smoke flows with the prevailing southeasterly surface winds at 3–4 m s−1, and forms ovoid plumes whose mean length, height, and cross-plume width are 41 km, 708 m, and 27% of the plume length, respectively. 50% of these plumes have length between 24 and 50 km, height between 523 and 993 m and width between 18% and 30% of plume length. Length and cross-plume width are lognormally distributed, while height follows a normal distribution. Borneo smoke plume heights are similar to previously reported plume heights, yet Borneo plumes are on average nearly three times longer than previously studied plumes. This could be due to sampling or to more persistent fires and greater fuel loads in peatlands than in other tropical forests. Plume area (median 169 km2, with 25th and 75th percentiles at 99 km2 and 304 km2, respectively) varies exponentially with length, though for most plumes a linear relation provides a good approximation. The MISR-estimated plume optical properties involve greater uncertainties than the geometric properties, and show patterns consistent with smoke aging. Optical depth increases by 15–25% in the down-plume direction, consistent with hygroscopic growth and nucleation overwhelming the effects of particle dispersion. Both particle single-scattering albedo and top-of-atmosphere reflectance peak about halfway down-plume, at values about 3% and 10% greater than at the origin, respectively. The initially oblong plumes become brighter and more circular with time, increasingly resembling smoke clouds. Wind speed does not explain a significant fraction of the variation in plume geometry. We provide a parameterization of plume shape that can help atmospheric models estimate the effects of plumes on weather, climate, and air quality. Plume age, the age of smoke furthest down-plume, is lognormally distributed with a median of 2.8 h (25th and 75th percentiles at 1.3 h and 4.0 h), different from the median ages reported in other studies. Intercomparison of our results with previous studies shows that the shape, height, optical depth, and lifetime characteristics reported for tropical biomass burning plumes on three continents are dissimilar and distinct from the same characteristics of non-tropical wildfire plumes.

scholarly journals Aerosol light-scattering enhancement due to water uptake during the TCAP campaign

2014 ◽  
Vol 14 (13) ◽  
pp. 7031-7043 ◽  
Author(s):  
G. Titos ◽  
A. Jefferson ◽  
P. J. Sheridan ◽  
E. Andrews ◽  
H. Lyamani ◽  
...  
Keyword(s):  
Optical Properties ◽  
Light Scattering ◽  
Climate Models ◽  
Single Scattering ◽  
Mean Value ◽  
Department Of Energy ◽  
Cape Cod ◽  
Hygroscopic Growth ◽  
Aerosol Optical Properties ◽  
Aerosol Parameters

Abstract. Aerosol optical properties were measured by the DOE/ARM (US Department of Energy Atmospheric Radiation Measurements) Program Mobile Facility during the Two-Column Aerosol Project (TCAP) campaign deployed at Cape Cod, Massachusetts, for a 1-year period (from summer 2012 to summer 2013). Measured optical properties included aerosol light-absorption coefficient (σap) at low relative humidity (RH) and aerosol light-scattering coefficient (σsp) at low and at RH values varying from 30 to 85%, approximately. Calculated variables included the single scattering albedo (SSA), the scattering Ångström exponent (SAE) and the scattering enhancement factor (f(RH)). Over the period of measurement, f(RH = 80%) had a mean value of 1.9 ± 0.3 and 1.8 ± 0.4 in the PM10 and PM1 fractions, respectively. Higher f(RH = 80%) values were observed for wind directions from 0 to 180° (marine sector) together with high SSA and low SAE values. The wind sector from 225 to 315° was identified as an anthropogenically influenced sector, and it was characterized by smaller, darker and less hygroscopic aerosols. For the marine sector, f(RH = 80%) was 2.2 compared with a value of 1.8 obtained for the anthropogenically influenced sector. The air-mass backward trajectory analysis agreed well with the wind sector analysis. It shows low cluster to cluster variability except for air masses coming from the Atlantic Ocean that showed higher hygroscopicity. Knowledge of the effect of RH on aerosol optical properties is of great importance for climate forcing calculations and for comparison of in situ measurements with satellite and remote sensing retrievals. In this sense, predictive capability of f(RH) for use in climate models would be enhanced if other aerosol parameters could be used as proxies to estimate hygroscopic growth. Toward this goal, we propose an exponential equation that successfully estimates aerosol hygroscopicity as a function of SSA at Cape Cod. Further work is needed to determine if the equation obtained is valid in other environments.

scholarly journals Effect of the summer monsoon on aerosols at two measurement stations in Northern India – Part 2: Physical and optical properties

2011 ◽  
Vol 11 (1) ◽  
pp. 1749-1775 ◽  
Author(s):  
A.-P. Hyvärinen ◽  
T. Raatikainen ◽  
M. Komppula ◽  
T. Mielonen ◽  
A.-M. Sundström ◽  
...  
Keyword(s):  
Optical Properties ◽  
Particle Concentration ◽  
Monsoon Season ◽  
Single Scattering ◽  
New Delhi ◽  
Particle Volume ◽  
Seasonal Behavior ◽  
Northern India ◽  
Surface Measurements ◽  
The Mean

Abstract. Aerosol physical and optical properties were measured at two locations in Northern India during 2006–2010. The first measurement station was a background site in Mukteshwar, about 350 km northeast of New Delhi, in the foothills of the Indian Himalayas. The second measurement site was located in Gual Pahari, about 25 km south of New Delhi. At both stations, the average aerosol concentrations during the monsoon were decreased by 40–75% compared to the pre-monsoon average concentrations. The decrease varied with the total local rainfall. Also the mean aerosol size decreased during the monsoon season. The size distribution at Mukteshwar was unimodal, with a mode diameter at about 80 nm. In Gual Pahari, the ratio of Aitken and accumulation particle concentration was >1, due to wet deposition and new particle formation during the monsoon season. Aerosol concentrations during the early monsoon were found to be affected by mineral dust which in Gual Pahari was observed as an increased particle volume at around 3–4 μm. The single scattering albedo varied from 0.73 to 0.93 during the monsoon season, being slightly lower in Gual Pahari than in Mukteshwar. The aerosol columnar properties, which were measured in Gual Pahari, showed a somewhat different seasonal behavior compared to the surface measurements, with the aerosol optical depth increasing to an annual maximum in the early monsoon season.

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