When I learn that New York City has an armed police branch that enforces recycling regulations, a vision immediately pops into my head. It’s a standoff in which a confused woman, on the verge of putting a recyclable can in with the general waste, is confronted by a loaded weapon and told: “Keep your hands where I can see them, ma’am, put the can in the recycling box, and no one gets hurt.” Of course, I know this is silly, and in truth I have little idea of what to expect on my day with the New York Sanitation Police...

As if he knows that the gun is the thing I find most intriguing, bewildering and disturbing about the job, one of the first things Sanitation Police Officer Michael Bristol does, sitting in his SUV at the start of his shift, is show me the gun holstered to his belt and ask me if it makes me feel safer. In truth, it makes me feel distinctly less safe, and I ask him why he needs it. “Because the bad guys have guns”, he responds. “Have you ever been shot at?” I ask. “Not yet”, he says, and I hope today won’t be any different (especially as I feel a bit ill-equipped without the bullet-proof vest the officers are required to wear).

Formed in 1936, the force is currently made up of 56 ‘peace officers’ with at least two years’ experience in the Sanitation Department and 600 hours of police training in, amongst other things, using batons and fire arms, self defense, summons writing, basic criminal law, sanitation law and health code violations. The officers are charged with enforcing all aspects of sanitation law, tackling offences as trivial as littering or mixing recyclable and non-recyclable waste (with fines, not guns) and as serious as dumping toxic waste. They also try to catch thieves that are taking a particular type of city property: recycling. This is the principal task I observe on my ‘ride along’.

Until late 2007, people caught stealing recyclables were merely issued with a US$100 (£63) court summons, but the amount proved too trivial to act as a deterrent to the theft of increasingly valuable materials. These days, anyone caught filling a vehicle with illegally-taken recyclables receives a $2,000 (£1,265) summons (for the first offence – it goes up to $5,000 (£3,160) thereafter) and their vehicle is impounded until they pay the fine, plus $15 (£9) daily expenses.

At the Sanitation Police Headquarters, tucked behind a mini amusement park at the bottom end of Brooklyn, just north of Coney Island, a couple of lots are full of impounded vehicles, some of which will never be collected and will eventually be destroyed. The most interesting specimen I see is a Mister Softee ice cream van, and Bristol tells me he’s “personally taken two buses, a garbage truck and a school bus” that were being used to transport stolen recyclables. He adds that he and his partner, PO Eddie Burke, normally impound at least one vehicle a day.

And so, we drive off in an unmarked car to scour the streets of Manhattan, looking for ‘bad guys’ stealing recycling. To my surprise, the hottest items are not valuable metals, but conveniently-bundled cardboard, which is selling for more than $100 (£63) a ton. Just this July, New York and New Jersey officials broke up a small ring of cardboard thieves who stole 900 tons, worth $103,000 (£65,130), over the course of a couple months.

Though he says theft of all recyclables is “getting so it’s difficult to keep up with”, Bristol explains that there’s a crime ring of Nigerian immigrants who are the biggest culprits in cardboard theft – the group, he claims, is also involved in identity theft and stealing cars, and another officer tells me that, in addition to getting money for the cardboard, they sometimes pack the stolen cars in it to disguise them as they’re exported overseas.

We reach Manhattan about three o’clock, a bit before the cardboard really starts coming out in front of commercial facilities, but there are still some bundles about, and we drive around the streets of Lower Manhattan “on a cardboard caper... like a search and destroy mission”, as Bristol puts it, looking for any suspicious activity.

His partner, whom we’ll meet in a bit, calls up with a tipoff that there’s a box truck with Pennsylvania plates in the area to look into, and we also follow a white, unmarked van that makes a ‘suspicious’ U-turn, though nothing comes of either of these. “In this business, you have to investigate everything”, Bristol says. I ask him what he looks out for and he says unmarked vans and trucks with out-of-state plates are considered suspicious, adding that racial profiling comes into it, but that, in general, “It’s hard to describe. You just kind of get a knack for it.”

As we’re driving around, eyes peeled, police radios are crackling in the background. One is used to communicate with the Sanitation Police base, and another is used “to monitor what’s going on around us – it keeps me alive”, Bristol says, explaining that they use the general police radio to steer clear of dangerous situations. He also uses it to find out what colour wrist band he needs to be wearing – every day, there’s a different band worn by all the city’s plainclothes police on the arm they’d use to draw their guns, so they can be identified by fellow police. Today’s colour is orange, and when we get to China Town, we meet up with a few other officers sporting the distinctive orange bands high up their gun arms.

After a hefty meal of dumplings and General Tso’s chicken, we emerge from an underground restaurant and, before continuing on the ‘cardboard caper’, PO Richard Quinlan issues a $100 court summons to the driver of a leaking van. It’s for polluting the local environment with melting ice from containers used to deliver fish. The ‘respondent’ – as those issued with summonses are known – stands by impassively throughout the process.

Bristol and Burke then drive off to investigate another tipoff received during lunch and I hop in PO Quinlan’s unmarked police SUV. He explains that he issues summonses “with discretion”, adding: “We’re here to educate, not harm people”, and that he gets a real sense of satisfaction when the local environment improves because of their patrolling.

Summonses for recycling theft are also issued with discretion. “Once recycling hits the sidewalk, it belongs to the city. And, anything put in a DSNY receptacle is technically city property”, Quinlan explains. This means that those ubiquitous scavengers you see in many American cities could technically be fined for retrieving recyclables for their five-cent deposits, but in practice this rarely, if ever, happens.

Instead, the San Cops go after the more prolific and organised thieves. Until a couple of years ago, metal was indeed the hot item, and Quinlan says nearly all the large electronics like refrigerators and air conditioners the city was called to pick up would be missing by the time the collectors arrived – taken (and dismantled in potentially hazardous ways) for their metal. The increased financial consequences have helped curb this, and, Quinlan notes: “Metal’s hard work – people who steal metal are normally just trying to eat.” Not so with this cardboard ring, which Quinlan notes “is the most organised thing I’ve ever seen” and results in a lot of lost income, both for the city and the licensed waste haulers who pay the municipality a yearly sum in the thousands to collect commercial recyclate.

As we’re weaving our way uptown, just past Union Square, Quinlan suddenly shouts: “They’re doing it, they’re doing it!” Out of the corner of my eye, I see men loading the back of a Budget rental truck with bundles of cardboard. We pull over to the side of the road, and shortly thereafter they pass us (thieves can gather up all the cardboard on a street in a matter of minutes). We start following them, taking down the license plate details and calling Bristol and Burke with our location and a description of the vehicle.

Officers will often follow vehicles for a while and collect pictures as evidence to bring to court if a respondent challenges a summons, but this truck looks like it’s already pretty full, so there’s no need to wait for them to get more – “Even if they make us”, Quinlan tells me, “it’s okay.” And ‘make’ us, I reckon they do, as they zip through a changing light and we have to use the siren to get pedestrians out of the way to turn after them. After a few more blocks, though, the other police car pulls up with lights flashing and sirens blaring, and the Budget truck pulls to the side of the busy shopping street.

Once the truck is stopped, the occupants and vehicle are searched to make sure they don’t have any weapons (these particular bad guys have no guns), and the plates are run to ensure the vehicle’s not stolen. The officers also run the respondents’ IDs on a system called EJustice (“people who do stupid things do a lot of stupid things”, Quinlan explains, meaning they might be wanted for felony), and then open the truck, take photos of the haul, as well as respondents’ IDs, and issue the summonses before taking the truck back to the impound lot.

It turns out we have stopped members of the organised crime ring the officers were telling me about earlier; Quinlan says he’s personally caught both the occupants of the vehicle stealing cardboard on two previous occasions, and throughout the process, the offenders look bored. In fact, they’re only animated when I try to take their picture, and Bristol notes that one of them looked like he wanted to run at first (in which case the police officers wouldn’t be inclined to give chase, but would still reclaim the recycling).

Start to finish, an impounding takes around two hours, including paperwork, and the respondents are allowed to go about an hour into the process. When the time comes, they sign their summonses ($5,000 each, although the rental company will be called to pick up the vehicle so it won’t stay impounded), collect their items in a bag and get ready to leave.

As he’s going, the driver says: “I’m done with this, I’m tired of this”, and Quinlan retorts: “That’s what you said the last time!” The tone seems very lighthearted, considering the respondents have just been caught in the act of stealing a vast amount of valuable material (again), and the driver jokingly says he’s happy for the police to take the cardboard if they just give him the rental truck, which costs him $800 to hire. Pleasantries exchanged, he walks off – without his truck and the roughly $1,000+ worth of cardboard it contains.

Quinlan tells me that the first time the police stop someone, the respondents tend to get angry, “but once they see we’re going to treat them with respect, it becomes a game, almost”. He adds, however: “That light interaction can easily turn into intense frustration and anger after five or six times, especially when you’re taken by the same cop.” Inevitably, this can lead to violence, and Quinlan says: “It’s by the grace of God that none [of the POs] has ever shot anyone.” He says some have been shot at, though, and Bristol was left out of work for seven months for a shoulder replacement, after some cardboard thieves tried to run him over.

Happily, the unbroken run of not being shot or using their guns continued during my time with the Sanitation Police force. By all accounts, it was just a typical day.