Table 2. Levels of dust and air pollutants and meteorological observations during the study period.

	Days	Mean	SD	25th percentile	Median	75th percentile
Dust extinction coefficients (/km)
Hokkaido	1199	0.012	0.014	0.003	0.008	0.015
Miyagi	873	0.011	0.016	0.003	0.006	0.012
Ibaraki	1333	0.017	0.014	0.007	0.016	0.025
Niigata	529	0.021	0.026	0.008	0.015	0.025
Toyama	1122	0.015	0.022	0.005	0.010	0.017
Shimane	1159	0.032	0.035	0.016	0.024	0.036
Nagasaki	1103	0.018	0.024	0.005	0.011	0.022
Spherical extinction coefficients (/km)
Hokkaido	1199	0.087	0.077	0.036	0.068	0.115
Miyagi	870	0.074	0.107	0.014	0.039	0.085
Ibaraki	1333	0.120	0.097	0.050	0.095	0.162
Niigata	529	0.133	0.095	0.051	0.122	0.199
Toyama	1122	0.059	0.061	0.016	0.045	0.083
Shimane	1159	0.112	0.077	0.056	0.097	0.152
Nagasaki	1103	0.086	0.071	0.038	0.069	0.115
SPM (µg/m3)
Hokkaido	1461	14.4	6.6	10.1	12.6	16.6
Miyagi	1461	21.2	11.4	13.2	18.4	26.4
Ibaraki	1461	23.8	12.7	14.7	20.7	29.7
Niigata	1461	22.2	11.5	13.9	19.8	27.5
Toyama	1461	19.9	11.6	11.4	16.9	25.4
Shimane	1461	23.5	13.4	14.3	20.5	29.2
Nagasaki	1461	28.7	14.7	18.6	24.9	34.7
NO2 (ppb)
Hokkaido	1461	11.4	4.8	7.9	10.3	14.0
Miyagi	1461	13.3	4.8	9.9	12.5	16.2
Ibaraki	1461	12.2	4.7	8.8	11.2	14.9
Niigata	1461	10.5	4.3	7.5	9.9	12.6
Toyama	1461	11.5	4.3	8.5	10.9	14.0
Shimane	1461	6.4	2.5	4.6	6.0	7.7
Nagasaki	1461	11.3	3.9	8.5	10.9	14.0
SO2 (ppb)
Hokkaido	1461	3.1	0.7	2.6	3.1	3.5
Miyagi	1461	1.0	0.5	0.7	0.9	1.2
Ibaraki	1461	3.4	1.0	2.7	3.3	3.9
Niigata	1461	2.0	0.8	1.5	1.9	2.4
Toyama	1461	1.8	0.7	1.4	1.7	2.2
Shimane	1461	1.4	1.2	0.7	1.1	1.7
Nagasaki	1461	3.3	1.1	2.5	3.1	3.9
Ox (ppb)
Hokkaido	1461	38.2	9.5	31.9	36.7	43.8
Miyagi	1461	44.1	12.0	36.5	42.4	50.9
Ibaraki	1461	49.4	16.0	38.7	46.1	57.0
Niigata	1461	48.5	12.0	40.4	46.4	55.2
Toyama	1461	51.7	13.5	41.8	49.6	60.4
Shimane	1461	50.8	13.5	41.3	48.3	59.2
Nagasaki	1461	47.5	15.1	38.2	46.2	57.6
Temperature Average (°C)
Hokkaido	1461	9.3	9.5	0.5	9.6	18.0
Miyagi	1461	12.6	8.2	5.0	12.9	19.5
Ibaraki	1461	14.0	8.0	6.6	14.4	20.9
Niigata	1461	14.1	8.6	6.2	14.1	21.8
Toyama	1461	14.5	8.8	6.7	14.9	22.0
Shimane	1461	15.2	8.3	7.8	15.4	22.2
Nagasaki	1461	17.6	7.8	11.0	18.0	24.6
Temperature Max (°C)
Hokkaido	1461	13.2	10.4	3.3	14.0	22.5
Miyagi	1461	16.6	8.4	9.3	17.4	23.3
Ibaraki	1461	18.9	7.7	12.2	19.2	25.1
Niigata	1461	17.8	9.0	9.8	18.4	25.5
Toyama	1461	19.0	9.3	10.9	19.9	26.5
Shimane	1461	19.8	8.7	12.3	20.6	26.8
Nagasaki	1461	21.4	7.9	14.7	22.1	28.1
Temperature Min (°C)
Hokkaido	1461	5.8	9.4	−2.6	5.4	14.2
Miyagi	1461	9.2	8.5	1.0	8.8	16.9
Ibaraki	1461	9.7	8.9	1.4	9.8	17.7
Niigata	1461	10.9	8.6	2.9	10.6	19.0
Toyama	1461	10.7	8.6	2.6	10.3	18.8
Shimane	1461	11.5	8.5	4.1	10.9	19.1
Nagasaki	1461	14.2	8.1	6.8	14.1	21.8
Humidity (%)
Hokkaido	1461	68.0	10.0	62	68	75
Miyagi	1461	72.6	13.2	63	73	83
Ibaraki	1461	72.6	12.1	65	75	82
Niigata	1461	69.5	8.9	64	70	76
Toyama	1461	78.6	10.2	73	79	86
Shimane	1461	73.9	8.9	69	74	80
Nagasaki	1461	67.2	11.6	59	67	76

SD, standard deviation; SPM, suspended particulate matter.