Research Papers

Influence of Green Roofs on Early Morning Mixing Layer Depths in Mexico City

[+] Author and Article Information
Williams Vázquez Morales

Centro de Ciencias de la Atmósfera,
Universidad Nacional Autónoma de México,
CDMX, 04510, México
e-mail: williams.vazquez@unicach.mx

Arón Jazcilevich

Centro de Ciencias de la Atmósfera,
Universidad Nacional Autónoma de México,
CDMX, 04510, México
e-mail: jazcilev@unam.mx

Agustín García Reynoso

Centro de Ciencias de la Atmósfera,
Universidad Nacional Autónoma de México,
CDMX, 04510, México
e-mail: agustin@atmosfera.unam.mx

Ernesto Caetano

Centro de Ciencias de la Atmósfera,
Universidad Nacional Autónoma de México,
CDMX, 04510, México
e-mail: caetano@unam.mx

Gabriela Gómez

Instituto de Geografía,
Universidad Nacional Autónoma de México,
CDMX, 04510, México
e-mail: gabyg@igg.unam.mx

Robert D. Bornstein

Department of Meteorology and Climatology,
San Jose State University,
One Washington Square,
San Jose, CA 95192-0104
e-mail: pblmodel@hotmail.com

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received January 12, 2016; final manuscript received September 15, 2016; published online October 13, 2016. Assoc. Editor: Jorge E. Gonzalez.

J. Sol. Energy Eng 138(6), 061011 (Oct 13, 2016) (10 pages) Paper No: SOL-16-1023; doi: 10.1115/1.4034807 History: Received January 12, 2016; Revised September 15, 2016

An urbanized version of MM5 (uMM5) was used at a 500 m horizontal grid-resolution to study effects on morning urban mixing depths and near roof-top stability from use of extensive green roofs in Mexico City, which is characterized by large Bowen ratios and high building storages. The model uses urban-morphology data, while building hydrothermal uMM5 input parameters were obtained from measurements over green and nearby conventional roofs. Evaluation of uMM5 predicted values against rooftop and planetary boundary layer (PBL) observations from extensive field measurement campaigns showed that the model performed reasonably well. Additional simulations were carried assuming that the roofs in entire urban neighborhoods were greened. Predicted mixing depths from these simulations, along with observed air pollution concentrations, were then used in a simple box model to evaluate potential green roof impacts on concentration. Results showed that green roofs produced an early morning (7–10 LST) cooling of up to 1.2 °C at rooftop levels, which reduced mixing depths during that period. Effects were greater on a day with weak synoptic forcing that on one 48 h later with strong synoptic forcing. The mixing-depth decreases produced increased box-model pollutant concentrations. While the green roofs did not elevate the observed concentrations of CO, SO2, and NO2 above World Health Organization (WHO) health standards, they did increase PM10, values (which were already above its standard) by as much as 8% from 7 to 9 LST, when local populations are normally exposed to peak concentrations. This study has applications in the analyses of building energy efficiency.

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Fig. 1

Urban land covering within domain uMM5 innermost D4, including SIMAT site (5, star) and urban garden areas: (1) Bosque de Chapultepec, (2) Parque España, (3) Parque México, and (4) Cementerio Francés; modeling results will be shown along vertical cut L–L′

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Fig. 2

(a) Satellite photograph showing measurement locations on green and conventional roofs in botanical garden area on UNAM campus and (b) green roof with succulent cactacea plants

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Fig. 3

Central Mexico MM5 modeling domains D1–D3 and uMM5 domain D4

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Fig. 4

Box model schematic, where all symbols are defined in text

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Fig. 5

Surface anticyclonic synoptic conditions over central Mexico (black circle) on Mar. 10, 2006, showing horizontal winds (1 barb = 10 m s−1) and omega vertical velocities (scale bar at right; downward motion is positive, Pa·s−1) at (a) 03, (b) 06, and (c) 09 LST

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Fig. 6

Measured Mar. 22, 2009 (a) virtual potential temperatures and (b) RHs, with solid line for green and dashed line for conventional roof simulations, same for (c) and (d), but for March 20.

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Fig. 7

Comparison of Mar. 8–16, 2006 average hourly (a) wind speed and (b) temperature for measurements at SIMAT station (circles), uMM5 (solid line), and MM5 (dashed line)

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Fig. 8

Modeled and measured (SIMAT site) fluxes Mar. 10, 2006 for (a) sensible and (b) latent heats, both for conventional roof case (CR dots), green roof case (GR triangles), and measurements (dashes); also shown are modeled CR (c) ground and (d) storage heat fluxes

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Fig. 9

Ceilometer backscatter and uMM5 PBL heights (km, solid line and then dots) for (a) March 12 and (b) March 14

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Fig. 10

Comparison of 06 to 11 LST uMM5 PBL heights for conventional (CR, dashes) and green roof (GR solid) cases on (a) Mar. 12, 2006 and (b) Mar. 14, 2006; enlarged view in (a) shows period with most significative differences

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Fig. 11

Simulated uMM5 potential temperature (°C) and PBL height (horizontal lines) for conventional (CR) and green (GR) roof cases for (a) March 12 at 0910 LST and (b) March 14 at 0840 LST; (c) and (d) show corresponding modeled TKE values (J/kg)

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Fig. 12

Percent reduction of maximum green roof uMM5 PBL heights for March 7–16, with time (LST) of maximum reduction indicated

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Fig. 13

Vertical cross section (along line L–L′ of Fig. 1) of modeled mixing heights for conventional (CR) and green (GR) roof cases for (a) March 12 and (b) March 14; location of site SIMAT also shown

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Fig. 14

Trends of CO, SO2, NO2, and PM10 concentrations at 07–10 LST for green (solid line) and observed/conventional (dashed line) roof cases for (a) March 12 and (b) March 14; horizontal dotted lines are WHO health norms




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