Walk down the streets almost anywhere in the District, and you won’t have to go far before you catch a whiff of a certain well-liked herb. Even before D.C.’s medical-marijuana law allows prescription pot, the scent of cannabis often drifts out of cars, hovers around the front of bars or wafts along sidewalks.

A federal study estimates 78,000 people in D.C. used pot in 2007, the last year for which statistics were available. That’s about 13 percent of the population at large; meanwhile, more than a quarter of 18-to-25-year-olds said they’d smoked in the last month alone.

Still, D.C. isn’t exactly Amsterdam: More per capita marijuana arrests are made in the District than in any other jurisdiction in the country, according to a recent analysis of MPD and FBI data by Shenandoah University criminal justice professor Jon Gettman, the former director of the National Organization for the Reform of Marijuana Laws. Pot arrests have been rising steadily every year since at least 2003, mirroring a national trend that began in the 1990s. And they didn’t really work. “We doubled marijuana arrests and it had no effect on the number of users,” Gettman says.

But even with a high arrest rate, some people in D.C. can probably safely get high without worrying that the cops are coming. Those people are white people. In 2007, 91 percent of those arrested for marijuana were black. In a city whose population demographics are steadily evening out, that’s odd. In fact, adjusting for population, African Americans are eight times as likely to be arrested for weed as white smokers are.

Even accounting for the number of people who move to D.C. for government or government-related jobs with security clearances that keep them from touching pot, that statistic comes as a surprise. The federal study—the National Survey on Drug Use & Health, produced by the Substance Abuse and Mental Health Administration—found pot use by black residents here is only slightly higher than white residents. (The study found 12.2 percent of black Washingtonians said they’d smoked in the last year, compared to 10.5 percent of whites.)

So why do black residents make up the vast majority of people arrested on marijuana charges? “It’s all about where the cops go fishing,” Gettman says.

Take some of the arrests made this past weekend, which were typical of the types of drug busts in the District:

• On Saturday morning, MPD officers executed a search warrant on the 20th Street NE digs of Michael Evans, 26. In the pocket of his blue jeans they found “a small plastic container containing green plant material,” according to charging documents. Evans admitted to cops that the weed was his, and was arrested.

• That afternoon, on 16th Street NE, Jeremy Platter, 22, was busted, court papers say. An officer from the First District vice squad had established an “observation post” where he saw a man smoking a blunt. “The unknown male subject then handed a blunt to D-2 (Jeremy Plater),” who started to smoke the blunt. When police closed in, “Plater was observed dropping the blunt from behind his back onto the ground and stepping on the blunt.”

• On Saturday evening, after allegedly failing to use his turn signal at about 11 o’clock in the 2300 block of 11th Street NW, Edward Whitaker, 22, of Woodbridge, Va., was arrested for marijuana possession. During the traffic stop, cops found “a small red zip of green leafy-like substance and brass knuckles” in his car door.

Of the six people who were arrested over the weekend for marijuana charges alone, all were African American. The unlucky six could face up to a year in jail and up to $1,000 in fines for possession, or a year in prison and $10,000 in fines for intent to distribute.

What’s clear from studying the stats and the arrest patterns is that who gets busted on marijuana charges basically comes down to where police are putting patrols, serving papers or making traffic stops—and who they’re stopping. Smoke a joint in the privacy of your Chevy Chase home, and the chances of a cop showing up to cuff you for it are practically zero. Spark a blunt while strolling down the street in Ivy City, though, and an officer who’s already in the area may well spot you.

Part of the discrepancy also comes from the way black and white Washingtonians buy, and use, weed. There aren’t any open-air drug markets in the city’s predominantly white neighborhoods, so people who live in, say, Forest Hills tend to buy pot from someone they know, behind closed doors.

MPD officials did not comment for this story by press time. But they say there’s nothing nefarious about the racial breakdown of the pot arrests. There’s a simple explanation, Assistant MPD Chief Peter Newsham told The Washington Post in 2007: It’s a lot easier to detect than, say, crack or heroin. “You can drop a rock and run,” Newsham told the Post. “If you drop a Ziploc bag of marijuana, you’re going to leave a big patch of green.”

But that doesn’t really seem to explain the whole situation. Between 2001 and 2009, the parts of D.C. that saw the greatest increases in arrests were Wards 5 and 7, according to a brief published earlier this year by the Justice Policy Institute, a group dedicated to “ending society’s reliance on incarceration.” Many of those arrests were for low-level pot charges. Those wards also happen to have significantly higher percentages of people of color than, say, Ward 3 or Ward 2, notes Tracy Velázquez, the group’s executive director.

Meanwhile, according to government drug abuse stats, racially diverse Wards 1 and 2 have a slightly higher percentage of monthly pot users than Wards 5 and 7. They also have a slightly higher percentage of users of illicit drugs other than marijuana.

“One thing about drug arrests is they’re proactive,” Velázquez says. “People are not going to call the police and say, ‘My neighbor is smoking pot.’” Because of that, she says, arresting pot smokers is about who cops decide to keep any eye on or search.

And in the District, apparently, that still means blacks more than whites.