scholarly journals Similarities and differences of aerosol optical properties between southern and northern sides of the Himalayas

2014 ◽  
Vol 14 (6) ◽  
pp. 3133-3149 ◽  
Author(s):  
C. Xu ◽  
Y. M. Ma ◽  
A. Panday ◽  
Z. Y. Cong ◽  
K. Yang ◽  
...  
Keyword(s):  
Optical Properties ◽  
Monsoon Season ◽  
Diurnal Variations ◽  
The Other ◽  
The Tibetan Plateau ◽  
Aerosol Optical Properties ◽  
Coarse Mode ◽  
Southern Side ◽  
Northern Side ◽  
The Himalaya

Abstract. The Himalaya mountains along the southern edge of the Tibetan Plateau act as a natural barrier for the transport of atmospheric aerosols from the polluted regions of South Asia to the main body of the Tibetan Plateau. In this study, we investigate the seasonal and diurnal variations of aerosol optical properties measured at two Aerosol Robotic Network (AERONET) sites on the southern side of the Himalaya (Pokhara, 812 m above sea level (a.s.l.) and EVK2-CNR, 5079 m a.s.l. in Nepal) and one on the northern side (Qomolangma (Mt. Everest) station for Atmospheric and Environmental Observation and Research, Chinese Academy of Sciences (QOMS_CAS) in Tibet, 4076 m a.s.l. in China). While observations at QOMS_CAS and EVK2-CNR can generally be representative of a remote background atmosphere, Pokhara is a lower-elevation suburban site with much higher aerosol load due to both the influence of local anthropogenic activities and to its proximity to the Indo-Gangetic Plains. The annual mean aerosol optical depth (AOD) during the investigated period was 0.05 at QOMS_CAS, 0.04 at EVK2-CNR and 0.51 at Pokhara, respectively. Seasonal variations of aerosols are profoundly affected by large-scale atmospheric circulation. Vegetation fires, peaking during April in the Himalayan region and northern India, contribute to a growing fine mode AOD at the three stations. Dust transported to these sites, wind erosion and hydrated/cloud-processed aerosols lead to an increase in coarse mode AOD during the monsoon season at QOMS_CAS and EVK2-CNR. Meanwhile, coarse mode AOD at EVK2-CNR is higher than at QOMS_CAS in August and September, indicating that the transport of coarse mode aerosols from the southern to the northern side may be effectively reduced. The effect of precipitation scavenging is clearly seen at Pokhara, which sees significantly reduced aerosol loads during the monsoon season. Unlike the seasonal variations, diurnal variations are mainly influenced by meso-scale systems and local topography. The diurnal pattern in precipitation appears to contribute to diurnal changes in AOD through the effect of precipitation scavenging. AOD exhibits diurnal patterns related to emissions in Pokhara, while it does not at the other two high-altitude sites. At EVK2-CNR, the daytime airflow carries aerosols up from lower-altitude polluted regions, leading to increasing AOD, while the other two stations are less influenced by valley winds. Surface heating influences the local convection, which further controls the vertical aerosol exchange and the diffusion rate of pollution to the surrounding areas. Fine and coarse mode particles are mixed together on the southern side of the Himalaya in spring, which may lead to the greater inter-annual difference in diurnal cycles of Ångström exponent (AE) at EVK2-CNR than that at QOMS_CAS.

scholarly journals Similarities and differences of aerosol optical properties between southern and northern slopes of the Himalayas

2013 ◽  
Vol 13 (8) ◽  
pp. 20961-21002
Author(s):  
C. Xu ◽  
Y. M. Ma ◽  
K. Yang ◽  
Z. K. Zhu ◽  
J. M. Wang ◽  
...  
Keyword(s):  
Optical Properties ◽  
Tibetan Plateau ◽  
Seasonal Variations ◽  
Monsoon Season ◽  
Diurnal Variations ◽  
The Other ◽  
The Tibetan Plateau ◽  
Coarse Particles ◽  
Aerosol Optical Properties ◽  
Coarse Mode

Abstract. The Himalayas is located at the southern edge of the Tibetan Plateau, and it acts as a natural barrier for the transport of atmospheric aerosols, e.g. from the polluted regions of South Asia to the main body of the Tibetan Plateau. In this study, we investigate the seasonal and diurnal variations of aerosol optical properties measured at the three Aerosol Robotic Network (AERONET) sites over the southern (Pokhara station and EVK2-CNR station in Nepal) and northern (Qomolangma (Mt. Everest) station for Atmospheric and Environmental Observation and Research, Chinese Academy of Sciences (QOMS_CAS) in Tibet, China) slopes of the Himalayas. While observations at QOMS_CAS and EVK2-CNR can generally be representative of a remote background atmosphere, Pokhara is an urban site with much higher aerosol load due to the influence of local anthropogenic activities. The annual mean of aerosol optical depth (AOD) during the investigated period was 0.06 at QOMS_CAS, 0.04 at EVK2-CNR and 0.51 at Pokhara, respectively. Seasonal variations of aerosols are profoundly affected by large scale atmospheric circulation. Vegetation fires, peaking during April in the Himalayan region and northern India, contribute to a growing fine mode AOD at 500 nm at the three stations. Dust transported to these sites results in an increase of coarse mode AOD during the monsoon season at the three sites. Meanwhile, coarse mode AOD at EVK2-CNR is higher than QOMS_CAS from July to September, indicating the Himalayas blocks the coarse particles carried by the southwest winds. The precipitation scavenging effect is obvious at Pokhara, which can significantly reduce the aerosol load during the monsoon season. Unlike the seasonal variations, diurnal variations are mainly influenced by meso-scale systems and local topography. In general, precipitation can lead to a decrease of the aerosol load and the average particle size at each station. AOD changes in a short time with the emission rate near the emission source at Pokhara, while does not at the other two stations in remote regions. AOD increases during daytime due to the valley winds at EVK2-CNR, while this diurnal variation of AOD is absent at the other two stations. The surface heating influences the local convection, which further controls the vertical aerosol exchange and the diffusion rate of pollutions to the surrounding areas. The Himalayas blocks most of the coarse particles across the mountains. Fine and coarse mode particles are mixed to make atmospheric composition more complex on the southern slope in spring, which leads to the greater inter-annual difference in diurnal cycles of Ångström exponent (AE) at EVK2-CNR than that at QOMS_CAS.

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 Closure on the single scattering albedo in the WRF-Chem framework using data from the MILAGRO campaign

2009 ◽  
Vol 9 (1) ◽  
pp. 5009-5054
Author(s):  
J. C. Barnard ◽  
J. D. Fast ◽  
G. Paredes-Miranda ◽  
W. P. Arnott
Keyword(s):  
Optical Properties ◽  
Black Carbon ◽  
Chemical Properties ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Aerosol Optical Properties ◽  
Mean Values ◽  
Coarse Mode ◽  
Fine Mode ◽  
Using Data

Abstract. Data from the MILAGRO field campaign, which took place in the Mexico City Metropolitan Area (MCMA) during March 2006, is used to perform a closure experiment between aerosol chemical properties and aerosol optical properties. Measured aerosol chemical properties, obtained from the MILAGRO T1 site, are fed to two different "chemical to optical properties" modules. One module uses a sectional approach and is identical to that used in the WRF-Chem model, while the other is based on a modal approach. This modal code is employed as an independent check on the WRF-Chem module. Both modules compute aerosol optical properties and, in particular, the single-scattering albedo, ϖ0, as a function of time. The single-scattering albedos are compared to independent measurements obtained from a photoacoustic spectrometer (PAS). Because chemical measurements of the aerosol coarse mode were not available, and the inlet of the PAS could not ingest aerosols larger than about 2 to 3 μm, we focus here on the fine-mode ϖ0. At 870 nm, the wavelength of the PAS measurements, the agreement between the computed (modal and WRF-Chem) and observed fine-mode ϖ0, averaged over the course of the campaign, is reasonably good. The observed ϖ0 value is 0.77, while for both modules, the calculated value was 0.75 resulting in a difference of 0.02 between observations and both computational approaches. This difference is less than the uncertainty of the observed ϖ0 values (6%, or 0.05), and therefore "closure" is achieved, at least for mean values. After adjusting some properties of black carbon absorption and mass concentration within plausible uncertainty limits, the two modules simulate well the diurnal variation of ϖ0, and the absorption coefficient, Babs, but are less successful in calculating the variation of the scattering coefficient, Bscat. This difficulty is probably caused by the presence of larger particles during the day when windblown dust is ubiquitous; this dust likely increases the proportion of large particles introduced into the PAS. The dust also contributes to a very large aerosol mass loading in the coarse mode, and neglect of the coarse mode may cause significant errors, estimated to be as large as 0.07, in the calculation and measurement of ambient ϖ0. Finally, the observed ϖ0 is compared to the ϖ0 computed by the full WRF-Chem model, which includes prognostic aerosol chemistry. Unlike the results discussed above, a comparison between observed and simulated ϖ0 values reveals major differences. This large discrepancy is probably due, in part, to poor characterization of emissions near the T1 site, particularly black carbon emissions.

scholarly journals Link between local scale BC emissions in the Indo-Gangetic Plains and large scale atmospheric solar absorption

2012 ◽  
Vol 12 (2) ◽  
pp. 1173-1187 ◽  
Author(s):  
P. S. Praveen ◽  
T. Ahmed ◽  
A. Kar ◽  
I. H. Rehman ◽  
V. Ramanathan
Keyword(s):  
Optical Properties ◽  
Radiative Forcing ◽  
Large Scale ◽  
Positive Impact ◽  
Monsoon Season ◽  
Regional Scale ◽  
Local Scale ◽  
Dry Season ◽  
Aerosol Optical Properties ◽  
Gangetic Plains

Abstract. Project Surya has documented indoor and outdoor concentrations of black carbon (BC) from traditional biomass burning cook stoves in a rural village located in the Indo-Gangetic Plains (IGP) region of N. India from November 2009–September 2010. In this paper, we systematically document the link between local scale aerosol properties and column averaged regional aerosol optical properties and atmospheric radiative forcing. We document observations from the first phase of Project Surya and estimate the source dependent (biomass and fossil fuels) aerosol optical properties from local to regional scale. Data were collected using surface based observations of BC, organic carbon (OC), aerosol light absorption, scattering coefficient at the Surya village (SVI_1) located in IGP region and integrated with satellite and AERONET observations at the regional scale (IGP). The daily mean BC concentrations at SVI_1 showed a large increase of BC during the dry season (December to February) with values reaching 35 μg m−3. Space based LIDAR data revealed how the biomass smoke was trapped within the first kilometer during the dry season and extended to above 5 km during the pre-monsoon season. As a result, during the dry season, the variance in the daily mean single scattering albedo (SSA), the ratio of scattering to extinction coefficient, and column aerosol optical properties at the local IGP site correlated (with slopes in the range of 0.85 to 1.06 and R2>0.4) well with the "IGP_AERONET" (mean of six AERONET sites). The statistically significant correlation suggested that in-situ observations can be used to derive spatial mean forcing, at least for the dry season. The atmospheric forcing due to BC and OC exceeded 20 Wm−2 during all months from November to May, supporting the deduction that elimination of cook stove smoke emissions through clean cooking technologies will likely have a major positive impact not only on human health but also on regional climate.

scholarly journals Fluorescent biological aerosol particle measurements at a tropical high-altitude site in southern India during the southwest monsoon season

2016 ◽  
Vol 16 (15) ◽  
pp. 9805-9830 ◽  
Author(s):  
A. E. Valsan ◽  
R. Ravikrishna ◽  
C. V. Biju ◽  
C. Pöhlker ◽  
V. R. Després ◽  
...  
Keyword(s):  
High Altitude ◽  
Meteorological Parameters ◽  
Monsoon Season ◽  
Aerosol Particles ◽  
Fungal Spores ◽  
Significant Proportion ◽  
Diurnal Variations ◽  
High Concentration ◽  
Sem Images ◽  
Coarse Mode

Abstract. An ultraviolet aerodynamic particle sizer (UV-APS) was continuously operated for the first time during two seasons to sample the contrasting winds during monsoon and winter to characterize the properties of fluorescent biological aerosol particles (FBAPs), at a high-altitude site in India. Averaged over the entire monsoon campaign (1 June–21 August 2014), the arithmetic mean number and mass concentrations of coarse-mode (> 1 µm) FBAPs were 0.02 cm−3 and 0.24 µg m−3, respectively, which corresponded to  ∼  2 and 6 % of total aerosol loading, respectively. Average FBAP number size distribution exhibited a peak at  ∼  3 µm, which is attributed to the fungal spores, as supported by scanning electron microscope (SEM) images, and these results are consistent with previous studies made for FBAPs. During 11 weeks of measurements the variability of the total coarse-mode particle number (TAP) concentration was high compared to that observed in FBAP number concentrations. The TAP and FBAP number concentrations measured at this site were strongly dependent on changes in wind direction and rainfall. During periods of westerly/southwesterly winds with heavy persistent rainfall, the TAP and FBAP concentrations exhibited very low values (1.3 and 0.005 cm−3, respectively) with no significant diurnal variations, whereas during periods of northerly winds with scattered rainfall FBAPs exhibited relatively high concentration values (0.05 cm−3) with pronounced diurnal variations, which were strongly coupled with diurnal variations in meteorological parameters. The campaign-averaged FBAP number concentrations were shown to correlate with daily patterns of meteorological parameters and were positively correlated with relative humidity (RH; R2  =  0.58) and negatively with temperature (R2  =  0.60) and wind speed (R2  =  0.60). We did not observe any significant positive correlation with precipitation as reported by previous researchers from selected areas. These measurement results confirm the fact that the ratio of PBAPs to TAP is strongly dependent on particle size and location and thus may constitute a significant proportion of total aerosol particles.

scholarly journals Diurnal variations of aerosol optical properties in the North China Plain and their influences on the estimates of direct aerosol radiative effect

2015 ◽  
Vol 15 (10) ◽  
pp. 5761-5772 ◽  
Author(s):  
Y. Kuang ◽  
C. S. Zhao ◽  
J. C. Tao ◽  
N. Ma
Keyword(s):  
Optical Properties ◽  
North China Plain ◽  
Early Morning ◽  
Diurnal Variations ◽  
Accurate Estimation ◽  
Diurnal Changes ◽  
Aerosol Optical Properties ◽  
Late Afternoon ◽  
The North ◽  
Temporal Coverage

Abstract. In this paper, the diurnal variations of aerosol optical properties and their influences on the estimation of daily average direct aerosol radiative effect (DARE) in the North China Plain (NCP) are investigated based on in situ measurements from Haze in China campaign. For ambient aerosol, the diurnal patterns of single scattering albedo (SSA) and asymmetry factor (g) in the NCP are both highest at dawn and lowest in the late afternoon, and quite different from those of dry-state aerosol. The relative humidity (RH) is the dominant factor which determines the diurnal pattern of SSA and g for ambient aerosol. Basing on the calculated SSA and g, several cases are designed to investigate the impacts of the diurnal changes of aerosol optical properties on DARE. The results demonstrate that the diurnal changes of SSA and g in the NCP have significant influences on the estimation of DARE at the top of the atmosphere (TOA). If the full temporal coverage of aerosol optical depth (AOD), SSA and g are available, an accurate estimation of daily average DARE can be achieved by using the daily averages of AOD, SSA and g. However, due to the lack of full temporal coverage data sets of SSA and g, their daily averages are usually not available. Basing on the results of designed cases, if the RH plays a dominant role in the diurnal variations of SSA and g, we suggest that using both SSA and g averaged over early morning and late afternoon as inputs for radiative transfer model to improve the accurate estimation of DARE. If the temporal samplings of SSA or g are too few to adopt this method, either averaged over early morning or late afternoon of both SSA and g can be used to improve the estimation of DARE at the TOA.

scholarly journals An Investigation of Vertically Distributed Aerosol Optical Properties over Pakistan Using CALIPSO Satellite Data

2020 ◽  
Vol 12 (14) ◽  
pp. 2183 ◽  
Author(s):  
Miao Zhang ◽  
Bo Su ◽  
Muhammad Bilal ◽  
Luqman Atique ◽  
Muhammad Usman ◽  
...  
Keyword(s):  
Optical Properties ◽  
Agricultural Land ◽  
Satellite Observation ◽  
Northern Region ◽  
Dust Storms ◽  
Southern Region ◽  
The Other ◽  
Aerosol Layer ◽  
Aerosol Optical Properties ◽  
Color Ratio

The vertically distributed aerosol optical properties are investigated over Pakistan utilizing the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) Level 2 products from 2007 to 2014. For a better understanding of the spatiotemporal characteristics of vertical aerosol layers, the interannual and seasonal variations of nine selected aerosol parameters such as the AOD of the lowest aerosol layer (AODL), the base height of the lowest aerosol layer (HL), the top height of the highest aerosol layer (HH), the volume depolarization ratio of the lowest aerosol layer (DRL), the color ratio of the lowest aerosol layer (CRL), total AOD of all the aerosol layers (AODT), the number of aerosol feature layers (N), the thickness of the lowest aerosol layer (TL), the AOD proportion for the lowest aerosol layer (PAODL) for both day and night times are analyzed. The results show AODT increased slightly from 2007 to 2014 over Pakistan, and relatively high AODT exists over the Punjab and Sindh (southern region), which might be owing to the high level of economic development, frequent dust storms, and profound agricultural activities (anthropogenic emissions). AODT increases from north to south. The reason may be that the southern region is rapidly urbanized and is near the desert. The northern region is dominated by agricultural land, and cities are usually semi-urbanized. The highest AODT appears in summer compared to the other seasons, and during daytime compared to nighttime. The HL and HH vary significantly, owing to the topography of Pakistan. The N is relatively large over Punjab and Sindh compared to the other regions, which might be caused by relatively stronger atmospheric convections. The spatial distribution of the TL showed an inverse relationship with the topography as lower values are observed over elevated regions such as Gilgit-Baltistan and Jammu-Kashmir. The value of the PAODL indicates that 77% of the total aerosols are mainly concentrated in the lowest layer of the atmosphere over Pakistan. The higher values of DRL and CRL indicate non-spherical and large particles over Balochistan and Sindh, which might be related to the proximity to the desert. This study provides very useful information about vertically distributed aerosol optical properties which could help researchers and policymakers to regulate and mitigate air pollution issues of Pakistan.

scholarly journals Link between local scale BC emissions and large scale atmospheric solar absorption

2011 ◽  
Vol 11 (7) ◽  
pp. 21319-21361 ◽  
Author(s):  
P. S. Praveen ◽  
T. Ahmed ◽  
A. Kar ◽  
I. H. Rehman ◽  
V. Ramanathan
Keyword(s):  
Optical Properties ◽  
Radiative Forcing ◽  
Large Scale ◽  
Positive Impact ◽  
Monsoon Season ◽  
Regional Climate ◽  
Regional Scale ◽  
Local Scale ◽  
Dry Season ◽  
Aerosol Optical Properties

Abstract. Project Surya has documented indoor and outdoor concentrations of black carbon (BC) from traditional biomass burning cook stoves in a rural village located in the Indo-Gangetic Plains (IGP) region of N. India from November 2009- September 2010. In this paper, we systematically document the link between local scale aerosol properties and column averaged regional aerosol optical properties and atmospheric radiative forcing. We report observations from the first phase of Project Surya to estimate the source dependent (biomass and fossil fuels) aerosol optical properties from local to regional scale. Data were collected using surface based observations of BC, organic carbon (OC), aerosol light absorption, scattering coefficient at the Surya village (SVI_1) located in IGP region, and satellite and AERONET observations at the regional scale (IGP). The daily mean BC concentrations at SVI_1 showed the large increase of BC during the dry season (December to February) with values reaching 35 μg m−3. Space based LIDAR data reveal how the biomass smoke is trapped within the first kilometre during the dry season and its extension to above 5 km during the pre-monsoon season. As a result during the dry season, the variance in the daily mean SSA and column aerosol optical properties at the local IGP site correlated (with slopes in the range of 0.85 to 1.06 and R2>0.4) well with the "IGP_AERONET" (mean of six AERONET sites), thus suggesting in-situ observations at few locations can be used to infer spatial mean forcing. The atmospheric forcing due to BC and OC exceeded 20 W m−2 during all months from November to May, leading to the deduction that elimination of cook stove smoke emissions through clean cooking technologies will likely have a major positive impact on health and the regional climate.

scholarly journals Quantifying the sensitivity of aerosol optical properties to the parameterizations of physico-chemical processes during the 2010 Russian wildfires and heatwave

2020 ◽  
Author(s):  
Laura Palacios-Peña ◽  
Philip Stier ◽  
Raquel Lorente-Plazas ◽  
Pedro Jiménez-Guerrero
Keyword(s):  
Optical Properties ◽  
Relative Humidity ◽  
Vertical Distribution ◽  
Dry Deposition ◽  
Linear Response ◽  
Convective Transport ◽  
The Other ◽  
Aerosol Optical Properties ◽  
Other Hand ◽  
Non Linear

Abstract. The impact of aerosol-radiation and aerosol-clouds interactions on the radiative forcing is subject to large uncertainties. This is caused by the limited understanding of aerosol optical properties and the role of aerosols as cloud condensation/ice nuclei (CCN/IN). On the other hand, aerosol optical properties and vertical distribution are highly related and their uncertainties come from different processes. This work attempts to quantify the sensitivity of aerosol optical properties (i.e. aerosol optical depth; AOD) and their vertical distribution (using the extinction coefficient, backscatter coefficient, and concentrations species profiles) to key processes. In order to achieve this objective sensitivity tests have been carried out, using the WRF-Chem regional fully coupled model by modifying the dry deposition, sub-grid convective transport, relative humidity and wet scavenging. The 2010 Russian heatwave/wildfire episode has been selected as case study. Results indicate that AOD is sensitive to these key processes in the following order of importance: 1) modification of relative humidity, causing AOD differences up to 0.6; 2) modification of vertical convection transport with AOD differences around  0.4; and 3) the dry deposition with AOD differences up to −0.35 and 0.3. Moreover, these AOD changes exhibit a non-linear response. Both, an increase and a decrease in the RH result in higher AOD values. On the other hand, both, the increase and offset of the sub-grid convective transport lead to a reduction in the AOD over the fire area. In addition, a similar non-linear response is found when reducing the dry deposition velocity; in particular, for the accumulation mode where the concentration of several species increases (while a decrease might be expected). These non-linear responses are highly dependent on the equilibrium of the thermodynamics system sulphate-nitrate-SOA (secondary organic aerosol). In this sense, small changes in the concentration of one species can strongly affect others, finally affecting aerosol optical properties. Changes in this equilibrium could come from modifications in relative humidity, dry deposition or vertical convective transport. By itself, dry deposition also presents a high uncertainty influencing the AOD representation.

scholarly journals Quantifying the sensitivity of aerosol optical properties to the parameterizations of physico-chemical processes during the 2010 Russian wildfires and heatwave

2020 ◽  
Vol 20 (16) ◽  
pp. 9679-9700
Author(s):  
Laura Palacios-Peña ◽  
Philip Stier ◽  
Raquel Lorente-Plazas ◽  
Pedro Jiménez-Guerrero
Keyword(s):  
Optical Properties ◽  
Relative Humidity ◽  
Vertical Distribution ◽  
Dry Deposition ◽  
Nonlinear Response ◽  
Convective Transport ◽  
The Other ◽  
Aerosol Optical Properties ◽  
Other Hand ◽  
The Impact

Abstract. The impact of aerosol–radiation and aerosol–cloud interactions on the radiative forcing is subject to large uncertainties. This is caused by the limited understanding of aerosol optical properties and the role of aerosols as cloud condensation/ice nuclei (CCN/IN). On the other hand, aerosol optical properties and vertical distribution are highly related, and their uncertainties come from different processes. This work attempts to quantify the sensitivity of aerosol optical properties (i.e. aerosol optical depth; AOD) and their vertical distribution (using the extinction coefficient, backscatter coefficient, and concentrations' species profiles) to key processes. In order to achieve this objective, sensitivity tests have been carried out, using the WRF-Chem regional fully coupled model by modifying the dry deposition, sub-grid convective transport, relative humidity, and wet scavenging. The 2010 Russian heatwave–wildfires episode has been selected as case study. Results indicate that AOD is sensitive to these key processes in the following order of importance: (1) modification of relative humidity, causing AOD differences of up to 0.6; (2) modification of vertical convection transport with AOD differences around −0.4; and (3) the dry deposition with AOD absolute differences of up to −0.35 and 0.3. Moreover, these AOD changes exhibit a nonlinear response. Both an increase and a decrease in the RH result in higher AOD values. On the other hand, both the increase and offset of the sub-grid convective transport lead to a reduction in the AOD over the fire area. In addition, a similar nonlinear response is found when reducing the dry deposition velocity; in particular, for the accumulation mode where the concentration of several species increases (while a decrease might be expected). These nonlinear responses are highly dependent on the equilibrium of the thermodynamics system sulfate–nitrate–SOA (secondary organic aerosol). In this sense, small changes in the concentration of one species can strongly affect others, finally affecting aerosol optical properties. Changes in this equilibrium could come from modifications in relative humidity, dry deposition, or vertical convective transport. By itself, dry deposition also presents a high uncertainty influencing the AOD representation.

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