during late spring and early summer
在春末夏初
以上为机器翻译结果，长、整句建议使用 人工翻译 。
The contents of H2S, SO2 and NH3 were significantly increase upon serious pollution of the rivers in late Spring, Summer and early Autumn. During this periods of time, serious acid rain appeared.
实验表明，河网污染最严重的晚春、夏、初秋季节，H2S、SO2、NH3的排放量明显增高，且在这段时间，恰好是酸雨频发、严重的时期。
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