I am new to Google Earth Engine.

I have a program for Atmosphere Monitoring. I have managed to pull data for historical data. However, I can't pull recent data e.g. (a couple of days, today , yesterday etc.), I get error:

Collection.toList: The value of 'count' must be positive. Got: 0.

As it says 'Near-Real-Time' that mean that the data must update many times a day? My final goal is to be able to pull data in (near) real time so that I can this data through some other program visualize it. Is that possible?

var pt = ee.Geometry.Point(23.72801716860135,37.984115295446216);


var starDate = '2023-02-20';
var endDate = '2023-02-21';

var Monthly = ee.ImageCollection('ECMWF/CAMS/NRT').select('total_aerosol_optical_depth_at_550nm_surface')
  .filterDate(starDate, endDate);


var allDates = ee.List(Monthly.aggregate_array('system:time_start'));

var allDatesSimple = allDates.map(function(date){
  return ee.Date(date).format().slice(0,10);


var getTemp = function(image) {

  // Reducing region and getting value
  var value_tmmx = ee.Image(image)
    .reduceRegion(ee.Reducer.first(), pt)
  return ee.Number(value_tmmx).multiply(0.1);


var count = Monthly.size();

var tmmx_list = Monthly.toList(count).map(getTemp);

print("tmmn_list", tmmx_list);

var paired = allDatesSimple.zip(tmmx_list);

print ("paired", paired);

var myFeatures = ee.FeatureCollection(paired.map(function(el){
  el = ee.List(el); // cast every element of the list
  return ee.Feature(null, {
    'date': ee.String(el.get(0)),



// Export features, specifying corresponding names.
"export_aerosol", //my task
"GEE_Folder", //my export folder
"aerosol2",  //file name

1 Answer 1


You didn't have any data for your date range, so count was 0, causing Monthly.toList(count) to fail.

A general best practice in EE is to avoid converting collections to lists. In this case, doing that actually directly solve your problem. You can convert your image collection to a feature collection directly like this:

var myFeatures = ee.ImageCollection('ECMWF/CAMS/NRT')
  .filterDate(starDate, endDate)
  .map(function(image) {
    var value_tmmx = ee.Image(image)
      .reduceRegion(ee.Reducer.first(), pt)
    return ee.Feature(null, {
      date: image.date().format('yyyy-MM-dd'),
      aerosol: ee.Number(value_tmmx).multiply(0.1)


  • Hi , thanks for your answer. I test the code and i get an error (ImageCollection (Error) User memory limit exceeded....or Empty date ranges ...)....However my final goal is to get real time data (same day).... Thanks again!
    – gek
    Feb 25 at 14:43

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