[1] Aerosol mixtures composed of coarse mode desert dust combined with fine mode combustion generated aerosols (from fossil fuel and biomass burning sources) were investigated at three locations that are in and/or downwind of major global aerosol emission source regions. Multiyear monitoring data at Aerosol Robotic Network sites in Beijing (central eastern China), Kanpur (Indo-Gangetic Plain, northern India), and Ilorin (Nigeria, Sudanian zone of West Africa) were utilized to study the climatological characteristics of aerosol optical properties. Multiyear climatological averages of spectral single scattering albedo (SSA) versus fine mode fraction (FMF) of aerosol optical depth at 675 nm at all three sites exhibited relatively linear trends up to ∼50% FMF. This suggests the possibility that external linear mixing of both fine and coarse mode components (weighted by FMF) dominates the SSA variation, where the SSA of each component remains relatively constant for this range of FMF only. However, it is likely that a combination of other factors is also involved in determining the dynamics of SSA as a function of FMF, such as fine mode particles adhering to coarse mode dust. The spectral variation of the climatological averaged aerosol absorption optical depth (AAOD) was nearly linear in logarithmic coordinates over the wavelength range of 440-870 nm for both the Kanpur and Ilorin sites. However, at two sites in China (Beijing and Xianghe), a distinct nonlinearity in spectral AAOD in logarithmic space was observed, suggesting the possibility of anomalously strong absorption in coarse mode aerosols increasing the 870 nm AAOD.Citation: Eck, T. F., et al. (2010), Climatological aspects of the optical properties of fine/coarse mode aerosol mixtures,

[1] Aerosol optical properties and the spectral behavior of the aerosol optical depth (AOD) over Kanpur, an urban-industrial city in the Ganga basin, have been presented for the first time. Measurements by the ground-based Aerosol Robotic Network (AERONET) during January 2001 to December 2003 show pronounced seasonal influence, with maximum dust loading during the premonsoon season (April-May). The distribution of AOD is found to be large with a mean value of 0.6 at 500 nm wavelength. The frequency distribution of the Å ngström parameter a reveals two modes (a < 1 dominant dusty condition and a > 1 urban aerosols). Diurnal variations of AOD, water vapor content (WVC), and Å ngström parameter show strong seasonal influence. Maximum variation of AOD is found during the monsoon season (presence of mixed types of aerosols), maximum variation of WVC is observed during the winter season (frequent changes in humidity and air pressure), and a shows maximum variations during the premonsoon (dust dominating the atmospheric optical conditions) season. The aerosol volume size distributions show two distinct modes, fine (geometric mean radii of 0.17 mm and standard deviation of 0.03) and coarse (geometric mean radii of 3.37 mm and standard deviation of 0.1), but during May-August (period of dust loading), a third mode (around 1-2 mm) appears because of hygroscopic growth of finer aerosols. The single-scattering albedo (SSA) is found to increase with wavelength in the presence of dust and shows a reverse trend in dust-free conditions. Refractive indices show the presence of dust as the main component during the premonsoon season and dominance of anthropogenic urbanindustrial aerosols during the winter season, when the optical state of the atmosphere is more absorbing. The aerosol parameters show distinct interannual variations, with increasing aerosol burden over the region. Aerosol loading over Kanpur is found to be controlled by the regional climatology.

[1] Dust storms are considered natural hazards, which affect day-to-day life for a short time from a few hours to a few days. They are common in India especially in the western Rajasthan Province, which is covered by the Thar Desert. In this paper, we present the effects of the dust events on the aerosol parameters retrieved over Kanpur (located in heart of the Indo-Gangetic basin) from ground-based Aerosol Robotic Network (AERONET) measurements. The aerosol parameters show strong seasonal variability in this region, with least spectral dependence of aerosol optical depth (AOD) during the premonsoon season, characterized by dust loading. The aerosol optical properties over the IndoGangetic basin are controlled by the diurnal and seasonal cycles of urban pollutants, but the dust storms are so significant that the local cycle is completely overshadowed. A rise in AOD by more than 50% and corresponding decrease in angstrom parameter by 70-90% have been observed after each dust event. The diurnal variations of AOD during the dust events have been found to be controlled by the onset of the dust storms. The changes in the single scattering albedo (SSA) and real n(l) and imaginary k(l) parts of the refractive index indicate that the 27 May 2002 event influences the optical state to be absorbing, whereas for the other four events the aerosols are found to be dominantly scattering in nature. SSA has been found to increase sharply at higher wavelengths (l > 440 nm) during the dust events, whereas n(l) and k(l) increase 2-3 times more at l = 440 nm compared to those at higher wavelengths. The contrasting change in the spectral variations of the optical properties is due to the difference in the nature of the aerosols loading during the events. Aerosol volume concentration at coarse mode is found to increase three times after the dust events, whereas no significant change has been observed in the volume concentration at fine mode. Concentration of the particulate matters less than 10 mm (PM 10 ) is also found to increase by $150 mg m À3 after each dust event except on the 27 May 2002 event, when heavy rainfall after the dust storm washed out the suspended particulate matters from the atmosphere, and the ground level PM 10 concentration was not influenced by the advected dust particles on that day. Aerosol index values in successive Total Ozone Mapping Spectrometer (TOMS) images over the region support the characterization of the aerosols in this region in terms of their optical properties, which are being transported over the Indo-Gangetic basin from the western Thar Desert and the Gulf regions depending upon the size of the particles, shown by the air mass trajectories.

[1] The Indo-Gangetic Plain (IGP) encompasses a vast area, (accounting for $21% of the land area of India), which is densely populated (accommodating $40% of the Indian population). Highly growing economy and population over this region results in a wide range of anthropogenic activities. A large number of thermal power plants (most of them coal fed) are clustered along this region. Despite its importance, detailed investigation of aerosols over this region is sparse. During an intense field campaign of winter 2004, extensive aerosol and atmospheric boundary layer measurements were made from three locations: Kharagpur (KGP), Allahabad (ALB), and Kanpur (KNP), within the IGP. These data are used (1) to understand the regional features of aerosols and BC over the IGP and their interdependencies, (2) to compare it with features at locations lying at far away from the IGP where the conditions are totally different, (3) to delineate the effects of mesoscale processes associated with changes in the local atmospheric boundary layer (ABL), (4) to investigate the effects of long-range transport or moving weather phenomena in modulating the aerosol properties as well as the ABL characteristics, and (5) to examine the changes as the season changes over to spring and summer. Our investigations have revealed very high concentrations of aerosols along the IGP, the average mass concentrations (M T ) of total aerosols being in the range 260 to 300 mg m À3 and BC mass concentrations (M B ) in the range 20 to 30 mg m À3 (both $5 to 8 times higher than the values observed at off-IGP stations) during December 2004. Despite, BC constituted about 10% to the total aerosol mass concentration, a value quite comparable to those observed elsewhere over India for this season. The dynamics of the local atmospheric boundary layer (ABL) as well as changes in local emissions strongly influence the diurnal variations of M T and M B , both being inversely correlated with the mixed layer height (Z i ) and the ventilation coefficient (V c ). The share of BC to total aerosols is highest ($12%) during early night and lowest ($4%) in the early morning hours. While an increase in the V c results in a reduction in the concentration almost simultaneously, an increase in Z imax has its most impact on the concentration after $1 day. Accumulation mode aerosols contributed $90% to the aerosol concentration at ALB, $77 % at KGP and 74% at KNP. The BC mass mixing ratio was $10% over all three locations and is comparable to the value reported for Trivandrum, a tropical coastal location in southern India. This indicates presence of submicron aerosols species other than BC (such as sulfate) over KGP and KNP. A cross-correlation analysis showed that the changes in M B at KGP is significantly correlated with those at KNP, located $850 km upwind, and ALB after a delay of $7 days, while no such delay was seen between ALB and KNP. Back trajectory analyses show an enhancement in M B associated with trajectories arriving from west, the farther from to the west they arr...

During a comprehensive aerosol field campaign as part of ISRO‐GBP, extensive measurements of aerosol black carbon were made during December 2004, for the first time, at Kanpur, an urban continental location in northern India. BC diurnal variation is associated with changes in boundary layer mixing and anthropogenic activities. BC concentration in Kanpur is comparable to those measured in other mega cities of India but much higher than in similar locations of Europe, USA and Asia. High BC concentration is found both in absolute terms (6–20 μg m−3) and mass fraction (∼10%) yielding very low single scattering albedo (0.76). The estimated surface forcing is as high as −62 ± 23 W m−2 and top of the atmosphere (TOA) forcing is +9 ± 3 W m−2, which means the atmospheric absorption is +71 W m−2. The short wave atmospheric absorption translates to a lower atmospheric heating of ∼1.8°K/day. Large surface cooling and lower atmospheric heating may have impacts to regional climate.

Abstract. Low-cost particulate matter (PM) sensors are promising tools for supplementing existing air quality monitoring networks. However, the performance of the new generation of low-cost PM sensors under field conditions is not well understood. In this study, we characterized the performance capabilities of a new low-cost PM sensor model (Plantower model PMS3003) for measuring PM 2.5 at 1 min, 1 h, 6 h, 12 h, and 24 h integration times. We tested the PMS3003 sensors in both low-concentration suburban regions (Durham and Research Triangle Park (RTP), NC, US) with 1 h PM 2.5 (mean ± SD) of 9 ± 9 and 10 ± 3 µg m −3 , respectively, and a high-concentration urban location (Kanpur, India) with 1 h PM 2.5 of 36 ± 17 and 116 ± 57 µg m −3 during monsoon and post-monsoon seasons, respectively. In Durham and Kanpur, the sensors were compared to a research-grade instrument (environmental β attenuation monitor, E-BAM) to determine how these sensors perform across a range of PM 2.5 concentrations and meteorological factors (e.g., temperature and relative humidity, RH). In RTP, the sensors were compared to three Federal Equivalent Methods (FEMs) including two Teledyne model T640s and a Thermo Scientific model 5030 SHARP to demonstrate the importance of the type of reference monitor selected for sensor calibration. The decrease in 1 h mean errors of the calibrated sensors using univariate linear models from Durham (201 %) to Kanpur monsoon (46 %) and post-monsoon (35 %) seasons showed that PMS3003 performance generally improved as ambient PM 2.5 increased. The precision of reference instruments (T640: ±0.5 µg m −3 for 1 h; SHARP: ±2 µg m −3 for 24 h, better than the E-BAM) is critical in evaluating sensor performance, and β-attenuation-based monitors may not be ideal for testing PM sensors at low concentrations, as underscored by (1) the less dramatic error reduction over averaging times in RTP against optically based T640 (from 27 % for 1 h to 9 % for 24 h) than in Durham (from 201 % to 15 %); (2) the lower errors in RTP than the Kanpur post-monsoon season (from 35 % to 11 %); and (3) the higher T640-PMS3003 correlations (R 2 ≥ 0.63) than SHARP-PMS3003 (R 2 ≥ 0.25). A major RH influence was found in RTP (1 h RH = 64 ± 22 %) due to the relatively high precision of the T640 measurements that can explain up to ∼ 30 % of the variance in 1 min to 6 h PMS3003 PM 2.5 measurements. When proper RH corrections are made by empirical nonlinear equations after using a more precise reference method to calibrate the sensors, our work suggests that the PMS3003 sensors can measure PM 2.5 concentrations within ∼ 10 % of ambient values. We observed that PMS3003 sensors appeared to exhibit a nonlinear response when ambient PM 2.5 exceeded ∼ 125 µg m −3 and found that the quadratic fit is more appropriate than the univariate linear model to capture this nonlinearity and can further reduce errors by up to 11 %. Our results have substantial implications for how variability in ambient PM 2.5 concentrations, reference monitor types, and meteorologi...

Abstract. The Moderate Resolution Imaging Spectroradiometer (MODIS) onboard EOS Terra measures global aerosol optical depth and optical properties since 2000. MODIS aerosol products are freely available and are being used for numerous studies. In this paper, we present a comparison of aerosol optical depth (AOD) retrieved from MODIS with Aerosol Robotic Network (AERONET) data for the year 2004 over Kanpur, an industrial city lying in the Ganga Basin in the northern part of India. AOD retrieved from MODIS (τ aMODI S ) at 0.55µm wavelength has been compared with the AERONET derived AOD (τ aAERON ET ), within an optimum space-time window. Although the correlation between τ aMODI S and τ aAERONET during the post-monsoon and winter seasons (R 2 ∼ 0.71) is almost equal to that during the pre-monsoon and monsoon seasons (R 2 ∼0.72), MODIS is found to overestimate AOD during the pre-monsoon and monsoon period (characterized by severe dust loading) and underestimate during the post-monsoon and winter seasons. The absolute difference between τ aMODI S and τ aAERON ET is found to be low (0.12±0.11) during the non-dust loading season and much higher (0.4±0.2) during dust-loading seasons. The absolute error in τ aMODI S is found to be about ∼25% of the absolute values of τ aMODI S . Our comparison shows the importance of modifying the existing MODIS algorithm during the dustloading seasons, especially in the Ganga Basin in northern part of India.

[1] High aerosol loading over the northern Indian subcontinent can result in poor air quality leading to human health consequences and climate perturbations. The international 2008 TIGERZ experiment intensive operational period (IOP) was conducted in the Indo-Gangetic Plain (IGP) around the industrial city of Kanpur (26.51°N, 80.23°E), India, during the premonsoon (April-June). Aerosol Robotic Network (AERONET) Sun photometers performed frequent measurements of aerosol properties at temporary sites distributed within an area covering ∼50 km 2 around Kanpur to characterize pollution and dust in a region where complex aerosol mixtures and semi-bright surface effects complicate satellite retrieval algorithms. TIGERZ IOP Sun photometers quantified aerosol optical depth (AOD) increases up to ∼0.10 within and downwind of the city, with urban emissions accounting for ∼10-20% of the IGP aerosol loading on deployment days. TIGERZ IOP area-averaged volume size distribution and single scattering albedo retrievals indicated spatially homogeneous, uniformly sized, spectrally absorbing pollution and dust particles. Aerosol absorption and size relationships were used to categorize black carbon and dust as dominant absorbers and to identify a third category in which both black carbon and dust dominate absorption. Moderate Resolution Imaging Spectroradiometer (MODIS) AOD retrievals with the lowest quality assurance (QA ≥ 0) flags were biased high with respect to TIGERZ IOP area-averaged measurements. MODIS AOD retrievals with QA ≥ 0 had moderate correlation (R 2 = 0.52-0.69) with the Kanpur AERONET site, whereas retrievals with QA > 0 were limited in number. Mesoscale-distributed Sun photometers quantified temporal and spatial variability of aerosol properties, and these results were used to validate satellite retrievals.Citation: Giles, D. M., et al. (2011), Aerosol properties over the Indo-Gangetic Plain: A mesoscale perspective from the TIGERZ experiment,