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141 | % Created by LI Xu
% Version 1.0
% September 10, 2026
% If you have any question about this code,
% please do not hesitate to contact me via E-mail:
% jeremy456@163.com
% Blog:
% http://blog.sciencenet.cn/u/lixujeremy
% http://lixuworld.blogspot.com/
% https://aqihub.info/indices/canada
clear;
clc;
close all;
timebegin=tic;
cur_data=date;
cur_time=fix(clock);
str1=sprintf('%s %.2d:%.2d:%.2d', cur_data, cur_time(4), cur_time(5), cur_time(6));
fprintf('Time Begin: ');
fprintf(str1);
fprintf('\n');
%% ============================================================
% Canadian AQHI from NO2, O3 and PM2.5 GeoTIFF rasters
%
% Required units:
% NO2 : ppb
% O3 : ppb
% PM2.5: ug/m^3
%
% Ideally each input raster is a 3-hour rolling mean.
%% ============================================================
% Source Directory
SouDir='input';
no2files=dir(fullfile(SouDir, 'NO2*'));
o3files=dir(fullfile(SouDir, 'O3*'));
pm25files=dir(fullfile(SouDir, 'PM*'));
for ii=1:numel(no2files)
no2path=fullfile(SouDir, no2files(ii).name);
o3path=fullfile(SouDir, o3files(ii).name);
pm25path=fullfile(SouDir, pm25files(ii).name);
[~, fname, ~]=fileparts(pm25path);
fname=strsplit(fname, '_');
fname=fname{end};
otpath=fullfile(SouDir, ['AQHI_', fname, '.tif']);
GenAQHICompute(no2path, o3path, pm25path, otpath);
disp(['[', num2str(ii), '/', num2str(numel(no2files)), ']~', otpath]);
end
fprintf('Time Begin: ');
fprintf(str1);
fprintf('\n');
cur_data=date;
cur_time=fix(clock);
str2=sprintf('%s %.2d:%.2d:%.2d', cur_data, cur_time(4), cur_time(5), cur_time(6));
fprintf('Time End: ');
disp(str2);
timespan=toc(timebegin);
fprintf('Time Span: %.4f s\n', timespan);
disp('******************************************************************');
function GenAQHICompute(no2path, o3path, pm25path, otpath)
%% 1. Read pollutant rasters
[NO2, R_NO2] = readgeoraster(no2path, ...
'OutputType', 'double');
[O3, R_O3] = readgeoraster(o3path, ...
'OutputType', 'double');
[PM25, R_PM25] = readgeoraster(pm25path, ...
'OutputType', 'double');
%% 2. Make sure the rasters have the same dimensions
if ~isequal(size(NO2), size(O3), size(PM25))
error('NO2, O3 and PM2.5 rasters must have the same dimensions.');
end
%% 3. Handle physically impossible negative concentrations
% Optional but usually sensible for interpolated/modelled concentration maps.
NO2(NO2 < 0) = 0;
O3(O3 < 0) = 0;
PM25(PM25 < 0) = 0;
%% 4. Identify pixels where all three pollutants are available
valid = isfinite(NO2) & isfinite(O3) & isfinite(PM25);
AQHI_raw = nan(size(NO2));
AQHI_raw(valid) = (10 / 10.4) .* 100 .* ...
( ...
(exp(0.000537 .* O3(valid)) - 1) + ...
(exp(0.000871 .* NO2(valid)) - 1) + ...
(exp(0.000487 .* PM25(valid)) - 1) ...
);
%% 6. Calculate the reported integer AQHI
AQHI = nan(size(AQHI_raw));
AQHI(valid) = round(AQHI_raw(valid));
info = geotiffinfo(no2path);
geotiffwrite( ...
otpath, ...
single(AQHI), ...
R_NO2, ...
'GeoKeyDirectoryTag', info.GeoTIFFTags.GeoKeyDirectoryTag);
end
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