Camden CO₂ PALM comparison

16 June 2019, 19:30 UTC · PALM 30-minute averages · 10 m nested grid

PALM is an atmospheric model that uses large-eddy simulation to represent the larger turbulent motions in the air. In cities, it can simulate how buildings shape wind and how turbulent air transports gases such as CO₂. Maronga et al. (2020)

Compare the baseline surrogate’s CO₂ concentrations with the PALM simulation at matching model heights. The maps and statistics cover valid atmospheric cells within Camden.

How to read this comparison. Error is surrogate minus PALM. Positive values indicate overprediction. Heights above 95 m are exploratory. This reference case includes training patches, so the results describe agreement for this case. Independent validation requires a held-out case.

Compare one height

Model height Open full-size map

PALM concentration, surrogate concentration and surrogate minus PALM error at 45 m — PALM and the surrogate use the same concentration scale within each height. The error scale is separate. Figures clip colours for readability, and metrics use the unclipped values.

Results by height

Download metrics CSV

Model height	Cells	PALM mean (ppm)	Surrogate mean (ppm)	Bias (ppm)	MAE (ppm)	RMSE (ppm)	Pearson r
5 m	0	No valid atmospheric cells inside Camden
15 m	0	No valid atmospheric cells inside Camden
25 m	323	422.514	423.007	0.493	1.032	1.432	0.966
35 m	15,765	422.021	421.960	-0.060	1.032	1.940	0.937
45 m	46,820	419.208	419.242	0.034	0.703	1.104	0.967
55 m	82,169	417.706	417.957	0.251	0.710	1.139	0.971
65 m	116,885	416.819	417.248	0.429	0.767	1.068	0.963
75 m	142,877	416.154	416.665	0.512	0.762	0.959	0.930
85 m	159,041	415.640	416.189	0.548	0.762	0.943	0.900
95 m	172,367	415.258	415.816	0.558	0.756	0.934	0.863
105 m · exploratory	184,977	414.958	415.507	0.548	0.759	0.979	0.815
115 m · exploratory	196,148	414.722	412.950	-1.772	1.860	2.160	0.632
125 m · exploratory	206,251	414.521	410.152	-4.369	4.467	4.870	0.331
135 m · exploratory	212,849	414.365	411.622	-2.744	3.124	3.566	0.259
145 m · exploratory	217,894	414.233	413.372	-0.861	1.899	2.269	0.186
155 m · exploratory	218,506	414.122	416.287	2.165	2.260	2.540	0.231

How agreement changes with height

Open the full-size figure of error, bias and spatial correlation by model height — Only 323 cells are available for comparison at 25 m. Agreement weakens from 115 m upward. Within the 5–95 m focus, the largest local absolute error was 83.52 ppm.

Comparison method

The PALM and surrogate fields share a grid and time, so the comparison matches cells directly. Model heights are fixed vertical coordinates. The distance above local ground varies with terrain.

MAE is mean absolute error, RMSE is root mean square error, and Pearson r measures spatial correlation. The Camden boundary is from the Office for National Statistics, May 2024.

PALM reference

Maronga, B., et al. (2020). Overview of the PALM model system 6.0. Geoscientific Model Development, 13, 1335–1372. doi:10.5194/gmd-13-1335-2020