Smoggy or Sublime? : Weather: For some, the sudden swelter is making it hard to breathe, but for others, it’s a day at the beach.

It was no time to be a working stiff or even a striving student. Monday was a day to be at the beach.

“I plan to spend all day sitting right here” at San Buenaventura State Beach, said Marcus Harrington, 27, who had just finished a math class at Ventura College. “I’m going to soak up this sun as long as I can. This outweighs algebra by about two tons.”

Sunny, warm temperatures and an absence of the usual June fog drew the lucky ones to the seashore on Monday as temperatures hovered in the mid-70s and skies were sunny and blue.

But in the east end of Ventura County, temperatures shot into the 90s and pollution was heavy enough to make the air unhealthful to breathe.

The heat and air pollution in Simi Valley, the smoggiest city in Ventura County, sent one woman’s lungs into spasms that landed her in the emergency room at Simi Valley Hospital on Monday morning, said Dr. Gurdip Flora, who treated the woman.

The woman, who is in her early 40s, has a history of asthma, Flora said. “She had been doing well, but this morning she just went out of control,” he said.

Four more patients with lung problems also called Monday to schedule visits, Flora said.

“We usually don’t see patients on Mondays,” he said. “But if the weather stays like this, we will probably be bombarded this week.”

He advised all those with health problems as well as the elderly to stay indoors on smoggy days, which are expected to continue for at least the first half of the week.

Although temperatures were expected to taper off slightly today and Wednesday throughout the county, the smoggy air will probably linger in the inland valleys, said Kent Field, a meteorologist with the Ventura County Air Pollution Control District.

“Not only is the air stagnant, but we’re still producing pollutants in Oxnard and Ventura and Camarillo, which will get pushed out to Simi in the afternoon,” he said. “And we’re also getting pollutants from Los Angeles County. And we are nearing the longest day of the year.”

All of which makes for smoggy days.

Ozone, the main component of smog, is produced when pollutants from cars and other sources mix in heat and sunlight. Ozone can constrict the body’s air passages, making it difficult for people with lung or allergy problems to breathe.

But along the coast, where the air quality was good, sun-seekers at Hollywood Beach welcomed the warm temperatures and clear skies.

“Perfect weather for a family outing,” said Megan Brasher of Oxnard, who pulled daughters Whitney, 3, and Olivia, 2, in a wagon after an hour on the hot sand. “Monday’s usually such a gloomy day, but today’s beautiful.”

to know they are part of the problem.”

Correspondent Andrew Blechman contributed to this article.