Variability of Urban Aerosols over Santiago, Chile: Comparison of Surface PM10 Concentrations and Remote Sensing with Ceilometer and Lidar

Muñoz, Ricardo C.; Alcafuz, Ricardo I.

doi:10.4209/aaqr.2011.08.0133

Cited by 30 publications

(18 citation statements)

References 28 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Chilean anthropogenic emissions of sulfate, organic, and other primary and secondary aerosols as well as their gaseous precursors (such as SO 2 , which oxidizes to sulfate) originate mainly from industrial and urban sources, including copper mining and the Santiago metropolis (Tsapakis et al, 2002;Schüller et al, 2008). Santiago's emissions combined with transport restricted by topography causes this city to have one of the largest mass loadings of PM 10 (aerosols smaller than 10 µm) in the world (> 50 µg m −3 in 2006, Muñoz and Alcafuz, 2012). Thus, the dynamic conditions that allow air from this region to advect over the SEP may lead to strong AIEs.…”

Section: R C George Et Al: Development and Impact Of Hooks Of Highmentioning

confidence: 99%

Development and impact of hooks of high droplet concentration on remote southeast Pacific stratocumulus

et al. 2013

View full text Add to dashboard Cite

Over the southeastern Pacific (SEP), droplet concentration (N_d) in the typically unpolluted marine stratocumulus west of 80° W (> 1000 km offshore) is periodically strongly enhanced in zonally elongated "hook"-shaped features that increase albedo. Here, we examine three hook events using the chemistry version of the Weather Research and Forecasting model (WRF-Chem) with 14 km horizontal resolution, satellite data, and aircraft data from the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx). A particularly strong hook yields insights into the development, decay, and radiative impact of these features. Hook development occurs with N_d increasing to polluted levels over the remote ocean primarily due to entrainment of cloud condensation nuclei (CCN) from the lower free troposphere (FT). The feature advects northwestward until the FT CCN source is depleted, after which N_d decreases over a few days due to precipitation and dilution. The model suggests that the FT CCN source supplying the hook consists of high concentrations of small accumulation-mode aerosols that contribute a relatively small amount of aerosol mass to the MBL, in agreement with near-coast VOCALS measurements of polluted layers in the FT. The aerosol particles in this hook originate mainly from a pulse of offshore flow that transports Santiago-region (33–35° S) emissions to the remote marine FT.

To provide pollution CCN that can sustain hooks, the FT transport of pollution plumes to the remote ocean requires strong, deep offshore flow. Such flow is favored by a trough approaching the South American coast and a southeastward shift of the climatological subtropical high-pressure system. The model simulations show precipitation suppression in the hook and a corresponding increase in liquid water path (LWP) compared with a simulation without anthropogenic sources. LWP also increases as the hook evolves over time due to increasing stability and decreasing subsidence. WRF-Chem suggests that dimethyl sulfide (DMS) significantly influences the aerosol number and size distributions in a hook, but that hooks do not form without FT CCN. The Twomey effect contributes ~ 50–70% of the albedo increase due to the presence of the hook, while secondary aerosol indirect effects and meteorological influences also contribute significantly.

The source of hook aerosols is difficult to determine with the available observations alone. The model provides further explanation of the factors influencing hook formation. Two other weaker hooks during VOCALS-REx are not as well simulated but are also associated with FT offshore flow near Santiago. Hooks demonstrate the importance of free-tropospheric transport of aerosols in modulating the droplet concentration in the southeastern Pacific stratocumulus deck, and present a formidable challenge to simulate accurately in large-scale models

show abstract

Section: R C George Et Al: Development and Impact Of Hooks Of Highmentioning

confidence: 99%

Development and impact of hooks of high droplet concentration on remote southeast Pacific stratocumulus

et al. 2013

View full text Add to dashboard Cite

show abstract

“…The study by Seguel et al (2013) showed near surface ozone origin measured in the residual layer by ozonesondes that accumulates between the top of the mixed layer and the base of the subsidence inversion. Additionally, data from an elastic Light Detection and Ranging system, and a ceilometer over Santiago show unequivocal layers of aerosols above the mixed boundary layer (Muñoz and Alcafuz, 2012). The presence of residual aerosol layers may explain the simple model underestimate of AOD.…”

Section: Model Results and Their Validationmentioning

confidence: 99%

“…2), a complete meteorological station and a ceilometer (CL31 Väisälä) have been operational since 2007, allowing a climatology of the BLH (Muñoz and Undurraga, 2010), as well as an indication of aerosol loading (Muñoz and Alcafuz, 2012). These data are used in the simple model described in the next section.…”

Section: Datamentioning

confidence: 99%

“…BLH data are multi-year averages obtained from Muñoz and Undurraga (2010) and adjusted by a simple parameterization of the BLH diurnal cycle. As in the July 22 nd case we had ceilometer data, we take advantage of these data assuming a linear relationship between the ceilometer backscattering reflectance and the PM 10 concentration from the surface to the top of the boundary layer (Muñoz and Alcafuz, 2012).…”

Section: Simple Aerosol Optical Depth Modelmentioning

confidence: 99%

See 1 more Smart Citation

Satellite Retrievals of Aerosol Optical Depth over a Subtropical Urban Area: The Role of Stratification and Surface Reflectance

Escribano

Gallardo

Rondanelli

et al. 2014

Aerosol Air Qual. Res.

View full text Add to dashboard Cite

We explore the relationship between satellite retrievals of aerosol optical depth (AOD) and surface aerosol mass concentrations over a subtropical urban area, namely, Santiago, Chile (33.5°S, 70.6°W, 500 m.a.s.l.). We compare 11 years of AOD from the MODerate resolution Imaging Spectroradiometer (MODIS) with in situ particulate matter mass concentrations (PM). MODIS AOD reaches its maximum in summer and minimum in winter, the opposite of the annual cycle of surface PM. To improve our understanding of the relevant governing processes, we use a simple model that estimates the boundary layer (BL) AOD based on measured PM, relative humidity and BL height (BLH) as well as best estimates of aerosol composition, size distribution, and optical properties. Model results indicate that a weak annual AOD cycle is due to the opposite annual cycles in BLH and PM, which is largely supported by the Aerosol Robotic NETwork (AERONET) data collected in 2001 and 2002 in Santiago. We identify a possible bias linked to the operational estimate of surface reflectance that may lead to a spurious summer maximum in MODIS AOD over Santiago. This misfit in surface reflectance appears to affect not only Santiago but also a significant area of the semi-arid Southern South America. Sensitivity experiments with the simple model indicate an underestimate of simulated AOD as compared to AERONET data. This underestimate points to the possible role of residual aerosol layers in the AOD measured at the surface (not included in the simple model). Cirrus clouds appear not to play a significant role in explaining the MODIS AOD seasonality. The need for improved characterizations of aerosol properties and their temporal and spatial distribution in cities such as Santiago is emphasized.

show abstract

“…The evening transition and the stable ABLs over Santiago, on the other hand, have received much less attention, despite their large effect on the air pollution problem. Only recently, numerical modeling work (Saide et al, 2011) and observations with a ceilometer and a lidar (Muñoz and Alcafuz, 2012) are beginning to shed some light on the complex dynamics of the stable Santiago atmospheric boundary layer. The results have relevance from the point of view of the applied air pollution problem of Santiago.…”

Section: Discussionmentioning

confidence: 99%

Relative roles of emissions and meteorology in the diurnal pattern of urban PM₁₀: Analysis of the daylight saving time effect

Muñoz

2012

Journal of the Air & Waste Management Association

Self Cite

View full text Add to dashboard Cite

Daylight saving time (DST) is a common practice in many countries, in which Official Time (OT) is abruptly shifted 1 hour with respect to solar time on two occasions every year (in fall and spring). All anthropogenic emitting processes tied to OT, like job and school commuting traffic, abruptly change in this moment their timing with respect to solar time, inducing a sudden shift between emissions and the meteorological factors that control the dispersion and transport of air pollutants. Analyzing 13 years of hourly particulate matter (PM10) concentrations measured in Santiago, Chile, we demonstrate that the DST practice has observable nontrivial effects in the PM10 diurnal cycle. The clearest impact is in the morning peak of PM10 during the fall DST change, which occurs later and has on average a significant smaller magnitude in the days after the DST change as compared to the days before it. This decrease in magnitude is most remarkable because it occurs in a period of the year when overall PM10 concentrations increase due to generally worsening of the dispersion conditions. Results are shown for seven monitoring stations around the city, and for the fall and spring DST changes. They show clearly the interplay of emissions and meteorology in conditioning urban air pollution problems, highlighting the role of the morning and evening transitions of the atmospheric boundary layer in shaping the diurnal pattern of urban air pollutant concentrations.Implications: The effects of daylight saving time adjustments on the diurnal cycle of PM 10 measured in Santiago, Chile, have been shown through the analysis of 13 years of hourly concentration data for seven air quality monitoring stations distributed over the city. They constitute an empirical demonstration of the sensitivity of PM 10 levels to modifications in the emission patterns and, as such, help in evaluating emission control measures taken during pollution episodes, as well as in constraining the magnitude and time phases of emission estimates used in numerical dispersion models.

show abstract

Variability of Urban Aerosols over Santiago, Chile: Comparison of Surface PM10 Concentrations and Remote Sensing with Ceilometer and Lidar

Cited by 30 publications

References 28 publications

Development and impact of hooks of high droplet concentration on remote southeast Pacific stratocumulus

Development and impact of hooks of high droplet concentration on remote southeast Pacific stratocumulus

Satellite Retrievals of Aerosol Optical Depth over a Subtropical Urban Area: The Role of Stratification and Surface Reflectance

Relative roles of emissions and meteorology in the diurnal pattern of urban PM₁₀: Analysis of the daylight saving time effect

Contact Info

Product

Resources

About

Variability of Urban Aerosols over Santiago, Chile: Comparison of Surface PM10 Concentrations and Remote Sensing with Ceilometer and Lidar

Cited by 30 publications

References 28 publications

Development and impact of hooks of high droplet concentration on remote southeast Pacific stratocumulus

Development and impact of hooks of high droplet concentration on remote southeast Pacific stratocumulus

Satellite Retrievals of Aerosol Optical Depth over a Subtropical Urban Area: The Role of Stratification and Surface Reflectance

Relative roles of emissions and meteorology in the diurnal pattern of urban PM10: Analysis of the daylight saving time effect

Contact Info

Product

Resources

About

Relative roles of emissions and meteorology in the diurnal pattern of urban PM₁₀: Analysis of the daylight saving time effect