Month	Jan.	Feb.	Mar.		Apr.		May		Jun.		Jul.		Aug.		Sep.		Oct.		Nov.		Dec.
Average	0.002	0	0.004		0.005		0.007		0.044		0.153		0.1		0.606		0.038		0.006		0.002
Maximum	0.003		0	0.007		0.007		0.012		0.076		0.387		0.18		1.82		0.07		0.011		0
Minimum	0.002		0	0.003		0.004		0.004		0.012		0.029		0.03		0.043		0.01		0.004		0

6.1.2 Meteorological characteristics

In 2004, the climate in the Three Gorges Reservoir area was characterized by mild weather with less rainfall and higher-than-normal temperature. The temperature of most months of the year turned out to be normal. The rainfall in spring and autumn was less than historical average, and the rainfall in summer was a bit less than the historical average.

● Precipitation

The annual precipitation in the construction area totaled 885.8mm, 25.6% less than the historical average. The annual precipitation was quite uneven in the twelve months. To be specific, the rainfall in March, April and October decreased by more than 50%; July also saw obvious decline in precipitation. However, January experienced relatively more rainfall, and only one rainstorm hit the area in August throughout the whole year. A total of 131 days experienced rainfall with the maximum daily precipitation of 53.6mm on August 21. The longest period of rainy days was ten consecutive days occurring in July while the longest period without any precipitation lasted for 17 consecutive days in February.

● Temperature

The annual average temperature in the construction area was 17.3℃, 0.1℃ higher than the historical average. The highest temperature reached 40.3℃ on July 27, and the lowest temperature was -2.1℃ on January 27. There were 28 days experiencing thunderstorms in the whole year.

● Wind speed

The annual average wind speed was 1.5m/s with the extreme speed hitting 29.8m/s on July 9. The wind direction changed frequently over the year with the dominant wind direction of NNW, accounting for 20% of the total.

Table 6-3 Statistics of important meteorological elements in the Three Gorges Dam Area in 2004

Month		Jan.	Feb.	Mar.	Apr.	May	Jun.	Jul.	Aug.	Sep.	Oct.	Nov.	Dec.	Whole year
Temperature	Temperature (℃)	5.1	10.1	12.9	19.4	21.7	24.2	27.3	25.9	23	17.2	13.4	7.6	17.3
	Difference to the historical average (℃)	-0.8	1.9	1.3	1.9	-0.1	-1	-0.2	-1	-0.3	-0.5	0.9	-0.3	0.1
Precipitation	Precipitation (mm)	39	41	18.2	32.7	155	114.3	120.8	195.3	85.8	20.5	47.4	15.8	885.8
	Difference to the historical average (%)	77.9	19.2	-67.8	-64.7	4	-28.6	-42.4	-0.6	-14.4	-79.5	-1.3	-26.2	-25.6
Wind speed	Average (m/s)	1.5	1.6	1.7	1.6	1.5	1.3	1.2	1.4	1.4	1.5	1.6	1.7	1.5
	Maximum (m/s)	7	7.6	8.9	8.6	10.8	8.4	11.9	7.1	6.4	6.5	6.1	5.8	11.9
	Extreme (m/s)	12.3	13.6	14.5	14.2	18.3	14.7	29.8	11.1	11	9.7	9.5	10.5	29.8

6.2 Air Quality

The assessment of the ambient air quality of the construction area (including office buildings, residential areas and construction sites) was conducted in accordance with the "Ambient Air Quality Standards (GB3095-1996)".

In 2004, the annual average concentration of SO₂ in the construction area was 0.024 mg/m³, meeting Grade II national air quality standard. The annual average level of NO₂ was 0.022 mg/m³, meeting Grade I national air quality standard. The daily average concentration of SO₂ of all the days in 2004 met or was superior to Grade II national air quality standard. In addition, all the daily average concentrations of NO₂ met Grade I air quality standard in 2004.

The annual average concentration of total suspended particles (TSP) in the construction area was 0.323 mg/m³, inferior to Grade III air quality standard. Among them, all the daily average concentrations of TSP in office and residential areas met or were better than Grade III air quality standard with the exception of only one single day. In the construction area, the percentage of days with the daily average of TSP meeting Grade I air quality standard was 14.8%, that meeting Grade II air quality standard was 38.5%, that meeting Grade III air quality standards was 17.0% and that failing to meet Grade III standard was 29.6% of the total respectively.

The overall ambient air quality in the construction area during 2004 deteriorated to some extent compared with that of the previous year, which was subject to the excavation of the right bank construction projects. The annual average concentration of NO₂ remained unchanged; the annual average of SO₂ increased a bit, and the annual average level of the TSP rose by 47.5%. TSP remained as the dominant pollutant in ambient air of the construction area.

6.3 Water Quality

According to the "Environmental Quality Standards for Surface Water (GB3838-2002)", 13 items such as pH value, dissolved oxygen, ammonia nitrogen, COD, permanganate index, BOD₅, volatile phenol, cyanide, arsenic, hexavalent chromium, copper, lead and cadmium were included to assess the water quality in the construction area. Anionic surface-active agents were added to the list for the assessment of water quality of waters near or along the bank.

The water quality of all sections in mainstream of the Yangtze River and waters near the bank was good in 2004, all meeting or being superior to Grade II water quality standard. Compared with 2003, the concentration of suspended particles had a further drop while other monitoring indicators were relatively stable.

Table 6-4 Water quality of the mainstream sections of the Yangtze River in the construction area in 2004

Section name	The 1st quarter	The 2nd quarter	The 3rd quarter	The 4th quarter	Whole year
Taipingxi	Ⅰ	Ⅱ	Ⅱ	Ⅰ	Ⅱ
Dongyuemiao	Ⅱ	Ⅱ	Ⅱ	Ⅰ	Ⅱ
Letianxi	Ⅰ	Ⅰ	Ⅱ	Ⅰ	Ⅱ

Table 6-5 Water quality of alongshore water areas of the Yangtze River in the construction area in 2004