http://www.tums.ac.ir/
TEHRAN UNIVERSITY OF MEDICAL SCIENCES
SCHOOL OFPUBLIC HEALTH 1 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Application of LUR model for chronic exposure estimation to SO2 and
PM10 in Tehran, Iran
Hasan Amini
Seyed Mahmood Taghavi Shahri
Sarah Henderson
Masud yunesian
Institute for Environmental Research and School of Public Health
TUMS, Tehran, Iran
2 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Outline
Introduction Acute and chronic effects of air pollution
Four generations of epidemiological studies
Limitations of existing tools
Conceptual framework of LUR
Methods
Model development
Diagnostics
Results
Limitations
Works in progress and future works
US Iran Symposium on Air Pollution
in Megacities, 3-5th December
3
http://www.tums.ac.ir/
Introduction
Health consequences of exposure to air pollution:
Acute: Time series analysis (Ecological studies) studies
Chronic: Cohort and cross sectional studies
The importance of accurate exposure measurement
4 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Introduction Generations of air pollution epidemiology
(Irva Hertz-Picciotto in: Modern Epidemiology, 3rd Edition, 2008)
First generation studies (similar to infectious diseases): within-community comparisons using a before-and-after design
5 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Introduction Generations of air pollution epidemiology
(Irva Hertz-Picciotto in: Modern Epidemiology, 3rd Edition, 2008)
First generation studies (similar to infectious diseases): within-community comparisons using a before-and-after design
Second generation (comparing communities with higher versus lower pollutant levels): Many standards and Clean Air Act of 1970 in the United States
Individual and region specific confounders (some times >40)
6 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Introduction Generations of air pollution epidemiology
(Irva Hertz-Picciotto in: Modern Epidemiology, 3rd Edition, 2008)
First generation studies (similar to infectious diseases): within-community comparisons using a before-and-after design
Second generation (comparing communities with higher versus lower pollutant levels): Many standards and Clean Air Act of 1970 in the United States
Individual and region specific confounders (some times >40)
Third generation (comparisons over time within a given area): Good control of individual confounders
Problem of ecological confounders
Inability to evaluate chronic effects
7 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Introduction Generations of air pollution epidemiology
(Irva Hertz-Picciotto in: Modern Epidemiology, 3rd Edition, 2008)
First generation studies (similar to infectious diseases): within-community comparisons using a before-and-after design
Second generation (comparing communities with higher versus lower pollutant levels): Many standards and Clean Air Act of 1970 in the United States
Individual and region specific confounders (some times >40)
Third generation (comparisons over time within a given area): Good control of individual confounders
Problem of ecological confounders
Inability to evaluate chronic effects
Newer generations (cohorts in which individual-level data are integrated with community-based exposure data): Better exposure measurement (Land use regression models)
8 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Introduction : Limitation of existing tools for exposure
measurement in Tehran
The need to capture within cities variation on a large number of people (for cohort and cross sectional studies)
Insufficient number of monitoring stations to capture all individuals
Inadequacy of existing models for evaluation of personal exposure status in Tehran
9 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Introduction : Limitation of existing tools for exposure measurement
in Tehran-models
1. Proximity Based Assessment and Proxies
2. Geostatistical Interpolation Approaches Kriging, Spline, Inverse Distance Weighted, Theissen Triangulation
3. Dispersion Models Gaussian Plume
Eulerian (grid-cell)
LaGrangian or Puff Models
4. Integrated Meteorological-Emission (IME) Models
5. Hybrid Models
10 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Introduction: Number of papers indexed in Pubmed by year
0
10
20
30
40
50
60
2013?2013201220112010200920082007200620052004
papers
11
US Iran Symposium on Air Pollution in Megacities, 3-5th September
http://www.tums.ac.ir/
Conceptual framework: How does it work
Construct a model to estimate the averaged level of given pollutant at each monitoring station (Y) using predictor variables (X)
To measure the value of each variable in the final model for any location using digitalized map
Imputing these X values in the model to get the estimation of Y value
12 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Study Area Characteristics
•Largest and the Most Populated City of
Iran
•Resident Population is Roughly 8.7
million
•22 Districts
•Surface Area =612 km2
•Average Elevation =1200 m (Roughly)
•. . . .
13 US Iran Symposium on Air Pollution in Megacities, 3-5th
December
http://www.tums.ac.ir/
Methods
15
Air Pollution Data sources (Response Variables):
•Air Quality Control Company (AQCC) 16
•Department of Environment (DOE) 7
• We ran the Amelia II program (10 times for each
pollutant)
• 21 out of the 23 monitors were eligible for inclusion in the study
US Iran Symposium on Air Pollution in Megacities, 3-5th
December
http://www.tums.ac.ir/
Methods
17
US Iran Symposium on Air Pollution in Megacities, 3-5th
December
http://www.tums.ac.ir/
Methods
18
Response variables: • Annual-mean concentrations for PM10 and
SO2 were averaged from January 01, 2010 to
January 1, 2011 for all the monitors after
imputation for missing data
Predictor Variables: • Geographic attributes that were compiled
within GIS
US Iran Symposium on Air Pollution in Megacities, 3-5th
December
http://www.tums.ac.ir/
Methods
The mean of the 10 imputation-filled datasets was calculated
Warmer and cooler seasons
April through September
October through March
(Based on WHO guidelines for countries in the Northern hemisphere)
20 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Methods
210 potentially predictive variables (PPVs) in six classes and 73 sub-classes
Traffic Surrogates
Land Use
Distance Variables
Population Density
Product Variables
Geographic Location
21 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Methods
Traffic Surrogates
The vehicular network in buffers with
different radii around the air pollution
monitoring stations
22 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Methods
Land Use Ten land use types within buffers around the stations:
Residential
Green space
Urban facilities
Industrial/workshop
Official/commercial
Transportation
Military
Agriculture
Arid/undeveloped
Other
23 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Methods
Distance Variables
The distance (and natural logarithm of the
distance) from each station to all of the
Traffic Surrogate and Land Use types, and
to a variety of other features
(Due to exponential decay in air pollutant concentrations with increasing distance from pollution sources)
24 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Methods
Population Density
The total population; and the population
excluding unemployed people and children
less than five years of age
25 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Methods
Product Variables
The products of variables in the Traffic
Surrogates class divided by variables in the
Distance Variables class
26 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Methods
Geographic Location
The elevation of each monitoring site,
obtained from a digital elevation model of
Tehran in meters above sea level
A slope variable
27 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Methods
The raw GIS inputs were all in vector format
(Originating from the Japan International Cooperation Agency (JICA) and the Centre for Earthquake and
Environmental Studies of Tehran)
The final predictive variables were all in raster format with a horizontal resolution of 5 meters
28 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Methods: Model development and diagnostics
A step-by-step algorithm considered four key pieces of information:
Consistency with a priori assumptions about the direction of the effect for each variable
A p-value of < 0.1
Increases in R2 for a leave-one-out cross-validation (LOOCV)
A multicollinearity index called the variance inflation factor (VIF)
29 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Methods: Model development and diagnostics
The algorithm was programmed as a function in the R statistical package
A single variable linear regression model for each of the PPVs in the eligible pool (210 to begin)
Models check for consistency (with a priori assumptions, p-value and the variable with the strongest LOOCV R2 value
30 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Methods: Model development and diagnostics
All possible second variables were added to the retained single variable model, similarly
In the third step, all possible third variables were added to the two variable model, similarly
Each variable was also removed from the model, and the LOOCV R2 value was calculated
31 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Methods: Model development and diagnostics
If any of the resulting two variable models had a higher LOOCV R2 value than the model elevated from the second step, the elevated model was replaced and the third step was restarted
If not, the third step model with the highest LOOCV R2 value was elevated to the fourth step
This process was followed until the LOOCV R2
value could no longer be increased by the addition of further variables
32 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Methods: Model development and diagnostics - LOOCV
First we built a model using 20 stations omitting the first one
Then we estimated the level air pollution of omitted station (y) using the model (x)
Then we built the model again, omitting the second station and using the remaining other 20 stations
This process was repeated for all monitoring station
The Pearson correlation coefficient and its square was used as an index
33 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Mehtods: Model development and diagnostics
Multicollinearity:
If VIF greater than 10, that model was considered unacceptable
Sequentially removing each variable from the available pool of variables
stability check of the models:
Minimum, maximum, and coefficient of variation for the set of coefficients for the LOOCV
34 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Methods: Regression mapping
Raster cells outside of the buffer zones as null
All null values for the Distance Variables class were set to zero
All null values for the Product Variables class were set to the maximum values for the layers
The Raster Calculator of the ArcGIS Spatial Analyst extension was used
A quantification limit (QL) for predictions at the low end of the concentration distributions, defined as the lowest measured concentration divided by square root of 2
Very high predictions were set to 120% of the maximum observed concentrations
35 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Results
Of the 210 variables generated, 19 (9%) were significantly predictive in one or more of the LUR models
SO2 Annual: 6
SO2 cooler: 7
SO2 warmer: 7
PM10 annual:4
PM10 cooler:5
PM10 warmer:4 36 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Results
The adjusted R2 ranged from 0.83 to 0.93 for SO2 and ranged from 0.53 to 0.72 for PM10
models respectively
The R2 values for the leave-one-out cross validations ranged from 0.61 to 0.82 for the SO2 models, and from 0.48 to 0.63 for the PM10 models
37 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Results: Model stability
The minimum and maximum of the LOOCV coefficients had the same direction for all variables in all models
For SO2, the maximum coefficients of variation for the LOOCV coefficients in the annual, cooler season, and warmer season models were 12.2%, 10.2%, and 17.9%, respectively
For PM10, the maximum coefficients of variation for the LOOCV coefficients in the annual, cooler season, and warmer season models were 10.8%, 10.4%, and 8.5%, respectively
39 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Results: Estimated annual SO2 and PM10 concentrations from the
final land use regression models
40 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Limitations
Relatively small sample size (usually 20-100 monitoring stations have been used)
Using LOOCR R2 instead of Model adjusted R2 (as the LOOCV tends to be less in models with lower monitoring stations)
Using governmental monitoring stations (did not use location allocation approach)
41 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Works in progress using LUR
Deterioration of Multiple sclerosis
Low birth weight
Childhood Leukemia
Breast cancer
District specific life expectancy (in 22 districts)
42 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Future works
Construction of models for other criteria air pollutants
Construction of models capturing both spatial and temporal variations (real time LUR models)
Using location allocation approach
43 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
Aknowledgement
This was part a MS thesis at Theran University of Medical Sciences
We would like to express our appreciation to the organizers of this meeting
Also appreciate kind cooperation of: Department of Environment
Tehran Air quality Control Company
Tehran Municipality
And many other people and organizations who helped us 44 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
And Finally
Thank you all for your attention
and
Appreciate any questions, comments or suggestions
46 US Iran Symposium on Air Pollution
in Megacities, 3-5th December
http://www.tums.ac.ir/
US Iran Symposium on Air Pollution
in Megacities, 3-5th December
47
Top Related