From Twitter @yoockin: Yellow powder still remains in Tokyo

I saw an article on Fukushima Diary that there was a Twitter post by yoockin asking about yellow powder found near the gutter of the balcony in her child’s school.

【教えてください】昨年3月に騒ぎになった、”黄色い粉”を信頼できる計測器で測った方はいませんか？実は子供の学校の教室のベランダ排水溝付近に、いまだに残っているようなのです。都内私立です。

[Please tell me] Has anyone checked THE yellow powder, which was seen in March last year ? Near the gutter of the balcony in my child’s school, there is still yellow powder. A private school in Tokyo.

Does anyone know what this yellow powder might be? I also remember seeing this powder on the balcony of our house in Japan (North of Tokyo in Ibaraki) just before we evacuated on March 15th, 2011. After 1 year after the accident, how could this still remain in Tokyo? Many people said it was just pollen, but would pollen stay there a full year later?