This article shows that contemporaneous and lagged air pollution negatively affects the likelihood of German individual investors to log in and trade in their brokerage accounts, using intraday data and controlling for investor-, weather-, traffic-, and market-specific factors. A 1 SD increase in air pollution leads to a 1.3 percent reduction in the probability of logging in, which is larger than the response to a 1 SD increase in sunshine. We argue that changes in air pollution affect productivity in cognitively demanding tasks, such as trading. Our results are robust to macroeconomic productivity shocks, nonlinearities, or measurement error.

We investigate individual investors' decisions under time-varying ambiguity (VVIX) using plausibly exogenous forced mutual fund liquidations at a German brokerage. Investors reinvest 87% of forced liquidations when the refund occurs on a day of low ambiguity and 0% when it occurs on a day of high ambiguity. Instead of reinvesting, investors become inert and keep the refund in their cash holdings. The effect reverses approximately six months after the liquidation. If investors reinvest, they decrease their risk-taking under ambiguity. Our results are not driven by risk, rebalancing decisions, experiencing losses, or attention and are robust to alternative measures of ambiguity.