The phrase "aghast at how" is correct and usable in written English.
It can be used to express shock or horror at a particular situation or action.
Example: "She was aghast at how quickly the situation escalated into chaos."
Alternatives: "shocked by how" or "appalled at how".
Are you aghast at how faddish food is?
Cynthia was aghast at how her companions were able to ignore Ireland's troubles and pretend everything was nice and pleasant.
("Once again I am aghast at how little my daughter knows me, at what a desert her imagination must be").
The convert, who did not want his name used because he said his conversion could jeopardize his job, said he was "aghast at how sacrilegious the show was".
But the company's most ardent detractors are nutritionists aghast at how many sugar- and salt-infused products Kellogg has positioned as good-for-you food.
Hollywood's movie studios, which are used to dealing with scruffier crews like Pirate Bay, a Swedish outfit, are aghast at how professional the newcomer is.
The listener is left aghast at just how much Darwin got right.
In fact, I became aghast at just how fond I became of him".
With this sadness I pray that we as a humanity look beyond our limited thinking, just as Einstein, just as Tesla, just as Copernicus, to the aspects of human experience that underlie such pain -- to the very real brain illnesses that make people do things they normally wouldn't do -- to the contrasts we sit back aghast at and wonder -- how could such light go down in such darkness.
"I get absolutely aghast with how materialistic we have become, especially at Christmas".
Saltz, aghast, asks how they could not have realized that they pointed their sculpture at the vacancy in the skyline created by the absence of the twin towers.
